Claire Spottiswoode and colleagues introduce the ancient partnership between wild honeyguides and human honey hunters.

Yasmin Foster and Bruce C. Robertson introduce the enigmatic and critically endangered kākāpō - the world's only flightless parrot.

If you find a bird bone in deposits from the Cretaceous period (145-66 million years ago), chances are it will belong to an enantiornithine bird. This extinct group of birds was mostly arboreal and dominated terrestrial environments from 130 to 66 million years ago. With approximately 90 known genera, they account for more than half of the known diversity of Mesozoic birds. Yet, despite apparently out-competing birds more closely related to living species in most Cretaceous continental environments, enantiornithines mysteriously went extinct at the end of the Cretaceous, alongside all other non-neornithine (crown-bird) dinosaurs.

Have your ever felt as happy as a lark, feathered your nest or taken someone under your wing? As we watch birds, we cannot help but be struck by their uncannily familiar behaviors - singing, nest building, caring for their young - to name just a few. Songbirds - the oscine suborder of perching birds that constitute roughly half (∼4,000) of all known avian species - are noted for the songs that males and sometimes both sexes in this group sing to court mates and defend territory from rivals. Birdsongs contain several to many acoustically distinct syllables, typically organized into a stereotyped phrase, and span the same audio bandwidth that we exploit for speech and music, making them easy for us to hear and appreciate. Consequently, eavesdropping humans long ago detected the most striking parallel between songbirds and humans: juvenile songbirds learn to sing in a manner similar to a child learning to speak.

Joel Cracraft introduces the Hoatzin (Opisthocomus hoazin), an odd and enigmatic bird that defies classification.

Birds contribute prominently to the terrestrial soundscapes on Earth. The sounds can arise from different sources, such as drumming by woodpeckers, bill clapping by storks or feather vibrations in the courtship flights of snipes and hummingbirds. However, most avian sounds are generated in the avian vocal organ, the syrinx. Vocal behavior is used in many different contexts and features prominently in mate choice and reproduction. It is therefore thought to have played an important role in the remarkable diversification of birds.

While most birds do not have external genitalia, in a small number of species the males have penises, which can be either intromittent or non-intromittent. Brennan provides an overview of bird genitalia, including speculation about the evolutionary forces involved.

Johnson gives an overview of bird pollinators and the plant species they pollinate.

Interview with Dr. Trish O'Kane, Senior Lecturer at the University of Vermont and developer of the social justice program, Birding to Change the World.

There is no greater anomaly in nature than a bird that cannot fly" - thus spoke Richard Owen, towering figure of Victorian biology, second only to Charles Darwin, who related this quote in his Origin of Species. Owen, who later became a strident critic of Darwin's theory, knew what he was talking about. In 1839, he received a bone fragment from New Zealand. Through his superior anatomy skills, Owen inferred that this was the femur of a bird, but a bird that must have been incredibly big and hence unable to fly. As more bones arrived, Owen concluded that they belonged to a group of bird that we now know as 'moa', some of which stood almost twice as tall as him and were among the largest birds that ever lived (Figure 1).

The primary reliance of birds on vision is readily and frequently asserted. Casual observations of birds completing their everyday behaviours is sufficient to convince most observers that birds are using vision to control their key behaviours. This assertion is supported by evidence that in most bird species relatively large portions of their brains are devoted to the analysis of information from vision. Also, the so-called intelligent behaviours of birds seem to be based primarily upon visual information. Thus, gaining information from vision, and using it to guide sophisticated behaviours, is seen as a vital component of what makes birds so fascinating.

Florian Maderspacher introduces the 'birds' special issue.

Passeriformes, more commonly known as perching birds or passerines, are the most species-rich group of birds. Totaling nearly 6500 species, approximately two out of every three bird species is a passerine. Passerines are globally distributed and are among the most abundant birds at nearly every terrestrial location on Earth. Owing to their diversity, abundance and cosmopolitan distribution, passerines are among the most familiar of all birds and have figured prominently in both human culture and science. For example, humans have long been captivated by the beautiful songs of many passerines (such as the Common Nightingale (Luscinia megarhynchos) in Europe and the Wood Thrush (Hylocichla mustelina) of North America), and it is common in some cultures - although globally discouraged as ecologically damaging, especially when birds are captured directly from the wild - to keep passerines as pets. Nevertheless, the vocal prowess and frequent ability to thrive in captivity have made passerines important models for lab-based research ranging from neurobiology to genetics. In contrast, the diversity and accessibility of many passerine birds in the wild continue to make them among the best animal models for field-based studies of behavioral ecology, evolution, mating systems, life history, disease resistance, ecological and evolutionary responses to climate change, among many other fields.

Portugal describes the unique morphology and habits of the secretary bird, which kills its prey with lightning-quick kicks to the head.

Emily Doolittle introduces the many connections between bird song and human music.

Robert Fleischer and colleagues introduce the unique songbird fauna of Hawaii and the threats it faces.

In humans, culture can have a variety of meanings, from trends in music or art, to technological advances, to the ideologies and values that underpin a society. What all these meanings all have in common is that they encompass behaviours, skills and ideas that are not genetically determined, but rather learned from those around us, and shared in a group or society. Human societies also exhibit what is termed 'cumulative cultural evolution', when cultures build on themselves over generations of learners to exhibit more complex or effective behaviours, allowing us to go from a sled to a high-speed train, or from counting to calculus. But what about other species - do they also exhibit cultures?

There is a reason this primer is called 'The avian brain' and not 'The birdbrain' even though the latter term might be more accessible. The term birdbrain was long used as a derogative, yet I hope that this primer will inspire you to see it more as I do - as a compliment. This primer will take you on a short tour. First, I will explore superficial differences between birds and mammals. Then I will briefly mention the behavioral capabilities of birds and explain why the bird brain has the neural makeup to generate these behaviors. This will lead me to briefly describe some key neural circuits and structures and to conclude with the ongoing challenge to identify functional differences in the neural substrates of avian and mammalian cognition. The aim of this short article, therefore, is not to give a full review of the avian brain but rather to highlight important aspects with a focus on the comparison to the mammalian brain and cognition.

Organismal adaptations are the hallmark of natural selection. Studies of adaptations in avian systems have been central to key conceptual and empirical advances in the field of evolutionary biology and, over the past decade, leveraged the proliferation of a diversity of genomic tools. In this synthesis, we first discuss how the different genomic architectures of avian traits are relevant to adaptive phenotypes. A mutation's chromosomal location (e.g., microchromosomes or sex chromosomes) or its specific nature (e.g., nucleotide substitution or structural variant) will determine how it may evolve and shape adaptive phenotypes, and we review different examples from the avian literature. We next describe how the source of adaptive variation, whether from de novo mutations, existing genetic variation, or introgression from another species, can affect the evolutionary dynamics of a trait. Our third section reviews case studies where the genetic basis of key avian adaptive phenotypes (e.g., bill morphology or plumage coloration) have been revealed. We end by providing an outlook and identifying important challenges to this field, both by focusing on technical aspects, such as the completeness of genomic assemblies and the ability to validate genetic associations with new sources of data, as well as by discussing the existential threat posed to birds from habitat alteration and climate change.

Alexander Lees and Pramana Yuda introduce the songbird trade of Southern and Eastern Asia that is a major threat to regional bird populations.

Throughout recorded human history, birds have fascinated and inspired humans to dream of flying. The Greek myth of Daedalus and his son Icarus, who flew too close to the sun and fell to his death, first written by Diodorus (60-30 B.C.E.) and later poetically revised by Ovid (8 C.E.), evokes the dangers of hubris. Many indigenous peoples invoke spiritual qualities and protection ascribed to birds that were symbols of freedom and viewed as sacred messengers of the gods. As a student of bird flight, Leonardo da Vinci (1452-1519) was the first to document dynamic soaring by birds. And, subsequently, the flight of birds inspired human engineered pursuit of powered aircraft design, with the Wright Brothers being the first to design and achieve sustained flight at Kitty Hawk, NC, USA in 1903.

Parental care, a usefully imprecise catch-all term for behaviors performed by breeding adults that benefit their offspring, is a popular research area among behavioral ecologists. Across Class Aves, it takes many forms, ranging from warming the eggs during incubation - such that the embryo develops within and eventually escapes from its protective shell - to extensive post-hatching assistance, especially by providing food but also by protecting young from weather and predators (Figure 1). In this primer, I will address the evolutionary forces likely to have shaped the peculiar avian habit of involving both parents in substantial post-fertilization investments, rather than just one. For this, I will focus on the costs, benefits, and complex social dynamics associated with elaborate parental care to show that what we may regard as the simple nuclear family (mom, dad, and a few kids) is anything but simple.

Most vertebrates, including all mammals and birds, are sexually reproducing organisms. The implication of sexual reproduction is that an adult bird exists because a male transferred sperm to the reproductive tract of a female during copulation, one of the sperm fertilized an egg, and the ensuing embryo developed into an individual male or female that in turn can reproduce. This fundamental feature of sexual life - the need to bring together male and female units (genomes, gametes, individuals) in a sequence of interactions - is both fascinating and fraught with conflict, because selection acts on individuals to maximize their own lifetime reproductive success (or on individual units of DNA to maximize the number of copies of themselves that remain in the gene pool). As a consequence, a bewildering diversity of reproductive traits and behaviours has evolved.

Much of the awe that humans have for the flight of birds derives from our earthbound habits and our bias toward emphasizing visual cues for interpreting processes in the world. Although we move through it and breathe it, air is vastly less dense than our bodies, so it is fanciful to imagine moving our limbs in a manner that would enable us to support our weight in the air. Moreover, air is invisible to us unless we use special tools to reveal its flow patterns. As evidence of our visual bias, contemplate a strong wind. You probably form a mental image of leaves moving on tree branches, or dust swirling about in a tornado, in both cases, solids moving in response to the force of the wind rather than the essence of the wind itself.

Bird migrations are impressive behavioral phenomena, representing complex spatiotemporal strategies to balance costs of living while maximizing fitness. The field of bird migration research has made great strides over the past decades, yet fundamental gaps remain. Technologies have sparked a transformation in the study of bird migration research by revealing remarkable insights into the underlying behavioral, cognitive, physiological and evolutionary mechanisms of these diverse journeys. Here, we aim to encourage broad discussions and promote future studies by highlighting research fields that are characterized by major knowledge gaps or conflicting evidence, namely the fields of navigation, social learning, individual development, energetics and conservation. We approach each topic by summarizing the current state of knowledge and provide a future outlook of ideas and state-of-the-art methods to further advance the field. Integrating knowledge across these disciplines will allow us to understand the adaptive abilities of different species and to develop effective conservation strategies in a rapidly changing world.

Finding the kitchen refrigerator in the middle of a sleepless night or arriving at the home parking lot at the end of a daily drive are things that we mostly take for granted. However, such feats rely on complex brain computations that integrate multiple environmental and internal cues. Together these computations mediate the process referred to as spatial cognition, the study of which has been one of the most active research fields in modern neuroscience. In the early 1970s, John O'Keefe recorded the activity of individual cells in the hippocampus of a freely moving rat: he found cells that fired action potentials when the rat passed through a specific place in the environment. Examining the activity pattern of such 'place cells', he concluded that the hippocampus may contain a 'cognitive map' that represents the animal's location in its proximate environment. Since O'Keefe's seminal discovery about half a century ago, extensive research has led to a detailed characterization of hippocampal space processing in rats and other mammalian species.

Observing the behaviour of others is a cheap and effective way of acquiring up-to-date information about the environment. Further, an animal that changes its behaviour in response to acquiring social information effectively propagates that information forwards. Although the rules that govern how individual birds detect and respond to social cues are often very simple, they are able to produce a diverse range of collective actions from which individuals can reap benefits that include predator avoidance and more accurate estimations of the environment. Understanding how and why individual-level rules that favour the emergence of collective behaviour have evolved therefore requires knowledge of the ecological and social contexts in which they are expressed. The breadth of research on social behaviours in birds is an unparalleled window into the ecology of collective behaviour and provides many opportunities to test whether different species overcome different ecological challenges using similar social rules and whether the collective behaviours of birds can act as sensors for the environment.

Bird migration is one of the most amazing biological phenomena exhibited by organisms today, with birds as small as three grams travelling thousands of kilometers twice each year. Most people are familiar with this behaviour; they likely recognize the seasonal movements of birds each year and may have even witnessed specific migratory events (e.g., geese flying in their characteristic V-formations). What many people may not know is that bird migration has a strong genetic basis, especially in groups like songbirds who migrate alone and at night, preventing juveniles from following more experienced adult birds on their first migration. Successful migration also requires the coordinated function of many traits, not only behavioural traits like timing and orientation but also morphological and physiological traits to permit these long distance treks. Together, these traits comprise what has been called the 'migratory syndrome'. In this primer, we provide a broad overview of research on the genetics of migratory traits, from early experimental work to future functional assays and their importance for bird conservation. We focus primarily on songbirds as most work on the genetics of migration has been conducted with this group.

I once spent a summer studying gulls on Appledore Island in the Gulf of Maine, off the east coast of the United States. The rocky island is a breeding colony for herring gulls (Larus argentatus) and great black-backed gulls (Larus marinus), so I had a front-row seat to the dramas that unfolded as birds paired up, laid and incubated eggs, and raised chicks. I saw chicks hatch from large speckled eggs (Figure 1A), a Herculean feat that took over an hour. Eggs and chicks are extremely vulnerable, and many gull offspring do not survive. Now, when a gull soars past - or pilfers my sandwich at the beach - I appreciate the hurdles it overcame just to reach adulthood.

What do birds do for us? Some may find this an inappropriate or perhaps distasteful question, suggesting as it might that the importance or value of birds lies principally in the ways that they benefit people, and with perhaps an unspoken implication that if they do not do enough then we should not be too concerned as to what befalls them. Nonetheless, it seems vital to understand the benefits or enhancements to human wellbeing, commonly known as ecosystem services, that birds provide for two main reasons. First, birds are under high and increasing threat, and thus these ecosystem services are also under pressure; around 4% of the known bird species of the Late Pleistocene is estimated to have become extinct, a much higher percentage of local populations has been lost or seriously eroded, and around 13% of current extant bird species is considered globally threatened with extinction. Second, and arguably more importantly, our ability to answer the question of what birds do for us is in some sense a measure of how well we understand, and place adequate 'value' (in the broadest, and not simply an economic, sense) on, the interaction between people and birds, and more generally that between people and nature. Indeed, birds provide a particularly valuable test of such understanding because they have been subject to a long and rich history of human interest and study.

Actin networks adapt to resistance by becoming denser. A recent investigation shows that this mechanosensation relies on a force-sensitive mechanical ratchet of capping actin filaments to reorganize the network. This and other mechanical feedback mechanisms make actin-based protrusion amazingly robust.

A recent study has overturned a long-held view that two distinct modifications to photosynthesis are incompatible. The findings provide interesting new insights into trade-offs associated with photosynthetic metabolism, as well as likely routes by which evolution altered one of the most fundamental processes in biology.

Bird nests have long attracted human interest, both as beautiful creations and as important constructions. They are important constructions because avian parents use them to protect their developing eggs and young from the dangers presented by the elements and predators. Despite sharing these protective functions, however, bird nests can be remarkably structurally variable, being built from a wide diversity of materials, and placed in all manner of locations. For example, male Australian brush turkeys scrape material into large nest mounds, woodpeckers excavate holes, storks build stacks, sparrows and swallows build cups (but of different materials), while weavers weave their famous hanging baskets. Nests might be built in bushes or holes in trees, dangle from a branch, or sit on the ground. They might be solitary and hidden, or conspicuous, together housing hundreds of families (Figure 1).

Sauropod dinosaurs include the largest land animals to have walked the earth, mostly weighing 10-70 tons (e.g., Sander et al.1 and Carballido et al.2). Osteohistology suggests that derived physiological traits evolved near the origin of sauropod gigantism, including both rapid and uninterrupted growth from juvenile to adult with little developmental plasticity.1,3,4 This differs from the slower, seasonally interrupted growth of their direct ancestors, as evident in most non-sauropodan sauropodomorphs, which also show developmental plasticity in some groups. Accelerated but seasonally interrupted growth is present in Lessemsauridae, the sister clade to Sauropoda, which also attained giant adult body sizes (>10 tons).5 These observations suggest a correlation between giant size and accelerated growth. However, testing this evolutionary connection has been limited by the incomplete understanding of the growth patterns in some of the closest non-giant relatives of sauropods. We present the osteohistology of two such taxa, Aardonyx celestae and Sefapanosaurus zatronensis. Both exhibit highly vascularized woven-parallel complexes, with fibrolamellar complexes during early to mid-ontogeny, containing regular growth marks. These observations provide strong evidence for rapid but seasonally interrupted growth with limited developmental plasticity (indicated by the regular spacing of growth marks). Combined with our review of early branching sauropodomorph osteohistology, these results show that highly accelerated growth rates originated among smaller, non-sauropodan sauropodomorphs weighing 1 to 2 tons but preceded the origins of giant size (>10 tons). Therefore, the capacity for rapid bone tissue formation, a derived aspect of rapid growth seen in sauropods, did not evolve specifically to enable giant body sizes but may have been a prerequisite for them.

Birds are among nature's most social animals. They are renowned for their group migrations, their cooperative foraging, their communal roosting, their synchronous breeding aggregations, their precise parent-offspring interactions, their coordinated group defenses and their intricate territorial and courtship rituals. In these and other contexts, and indeed in most moments of their lives, birds' capacities to navigate complex social demands and relationships can tip the balance between health or sickness, between reproductive success or failure, between life or death. It is thus no surprise that birds have evolved sophisticated systems for mediating social interactions. Foremost among these are communication signals, most evident in birds as songs, calls, color patterns and postural displays. These and other communication signals can transmit information about a signalers' status, motivations and possible future actions, for sensory and cognitive processing by signal receivers. In general, signals provide benefits for both signal senders and receivers. Consider the bright spring plumage of a male wood warbler who has established a breeding territory. The male's plumage pattern benefits him by signaling his 'ownership' of his territory, which can help him attract potential mates and preempt conflict with potential rivals. His plumage pattern also benefits his intended audiences: it informs females about the signaler's potential as a mate, and it informs other males about the degree of threat they might face were they to attempt a territory take-over. Communication signals are, in essence, a glue that maintains the cohesion of bird societies, and a currency that mediates sophisticated relationships within.

The mechanisms by which plants sense the pH of their environment remained largely obscure. A recent study revealed that plants employ an interlaced bimodal peptide-receptor system to monitor the pH of the root apoplast, a readout that prioritizes either growth or defense.

Comment on Curr Biol. 2022 Oct 24;32(20):4397-4410.e5.

The first studies to retrieve genome-wide data from two Medieval European Jewish communities from England and Germany illustrate the complex interplay of ancestry, disease, religion, culture and ethics.

The dramatic cell-shape changes involved in mitosis and cell division challenge the integrity of epithelial tissues. A new study reveals a surprising role for atypical protein kinase C in keeping apical contractility in balance and thus preventing epithelial disruption.

Symbiotic nitrogen fixation provides large amounts of nitrogen for global agricultural systems with little environmental or economic costs. The basis of symbiosis is the nutrient exchange occurring between legumes and rhizobia, but key regulators controlling nutrient exchange are largely unknown. Here, we reveal that magnesium (Mg), an important nutrient factor that preferentially accumulates in inner cortical cells of soybean nodules, shows the most positive correlation with nodule carbon (C) import and nitrogen (N) export. We further identified a pair of Mg transporter genes, GmMGT4 and GmMGT5, that are specifically expressed in the nodule cortex, modulating both nodule Mg import and C-N transport processes. The GmMGT4&5-dependent Mg import activates the activity of a plasmodesmata-located β-1,3-glucanase GmBG2 and consequently keeps plasmodesmata permeable for C-N transport in nodule inner cortical cells. Our studies discovered an important regulating pathway for host plants fine-tuning nodule C-N trading to achieve optimal growth, which may be helpful for optimizing nutrient management for soybean production.

An enduring question in the study of human evolution is why tool use evolved. A new study has found that stone tools improve diet quality in wild capuchin monkeys. Tools may have similarly increased the nutritional security in ancestral hominins.

Comment on Curr Biol. 2022 Oct 24;32(20):4473-4482.e7.

Elevated atmospheric CO2 enhances photosynthetic rate,1 thereby increasing biomass production in plants. Nevertheless, high CO2 reduces the accumulation of essential nutrients2 such as phosphorus (P),3 which are required for photosynthetic processes and plant growth. How plants ensure enhanced growth despite meager P status remains enigmatic. In this study, we utilize genome-wide association analysis in Arabidopsis thaliana to identify a P transporter, PHT4;3, which mediates the reduction of P in chloroplasts at high CO2. Decreasing chloroplastic P fine-tunes the accumulation of a sugar-P metabolite, phytic acid, to support plant growth. Furthermore, we demonstrate that this adaptive mechanism is conserved in rice. Our results establish a mechanistic framework for sustainable food production against the backdrop of soaring CO2 levels across the world.

Despite the recent emergence of multiple cellular and molecular strategies to restore vision in retinal disorders, it remains unclear to what extent central visual circuits can recover when retinal defects are corrected in adulthood. We addressed this question in an Lrat-/- mouse model of Leber congenital amaurosis (LCA) in which retinal light sensitivity and optomotor responses are partially restored by 9-cis-retinyl acetate administration in adulthood. Following treatment, two-photon calcium imaging revealed increases in the number and response amplitude of visually responsive neurons in the primary visual cortex (V1). In particular, retinoid treatment enhanced responses from the ipsilateral eye, restoring the normal balance of eye-specific responses in V1. Additionally, the treatment rescued the modulation of cortical responses by arousal. These findings illustrate the significant plasticity of the adult central visual system and underscore the therapeutic potential of retinoid administration for adults with retinal diseases.

We report genome sequence data from six individuals excavated from the base of a medieval well at a site in Norwich, UK. A revised radiocarbon analysis of the assemblage is consistent with these individuals being part of a historically attested episode of antisemitic violence on 6 February 1190 CE. We find that four of these individuals were closely related and all six have strong genetic affinities with modern Ashkenazi Jews. We identify four alleles associated with genetic disease in Ashkenazi Jewish populations and infer variation in pigmentation traits, including the presence of red hair. Simulations indicate that Ashkenazi-associated genetic disease alleles were already at appreciable frequencies, centuries earlier than previously hypothesized. These findings provide new insights into a significant historical crime, into Ashkenazi population history, and into the origins of genetic diseases associated with modern Jewish populations.

Neurons in the retrohippocampal cortices play crucial roles in spatial memory. Many retrohippocampal neurons have firing fields that are selectively active at specific locations, with memory for rewarded locations associated with reorganization of these firing fields. Whether this is the sole strategy for representing spatial memories is unclear. Here, we demonstrate that during a spatial memory task retrohippocampal neurons encode location through ramping activity that extends across segments of a linear track approaching and following a reward, with the rewarded location represented by offsets or switches in the slope of the ramping activity. Ramping representations could be maintained independently of trial outcome and cues marking the reward location, indicating that they result from recall of the track structure. When recorded in an open arena, neurons that generated ramping activity during the spatial memory task were more numerous than grid or border cells, with a majority showing spatial firing that did not meet criteria for classification as grid or border representations. Encoding of rewarded locations through offsets and switches in the slope of ramping activity also emerged in recurrent neural network models trained to solve a similar spatial memory task. Impaired performance of model networks following disruption of outputs from ramping neurons is consistent with this coding strategy supporting navigation to recalled locations of behavioral significance. Our results suggest that encoding of learned spaces by retrohippocampal networks employs both discrete firing fields and continuous ramping representations. We hypothesize that retrohippocampal ramping activity mediates readout of learned models for goal-directed navigation.

Effective and stimulus-specific learning is essential for animals' survival. Two major mechanisms are known to aid stimulus specificity of associative learning. One is accurate stimulus-specific representations in neurons. The second is a limited effective temporal window for the reinforcing signals to induce neuromodulation after sensory stimuli. However, these mechanisms are often imperfect in preventing unspecific associations; different sensory stimuli can be represented by overlapping populations of neurons, and more importantly, the reinforcing signals alone can induce neuromodulation even without coincident sensory-evoked neuronal activity. Here, we report a crucial neuromodulatory mechanism that counteracts both limitations and is thereby essential for stimulus specificity of learning. In Drosophila, olfactory signals are sparsely represented by cholinergic Kenyon cells (KCs), which receive dopaminergic reinforcing input. We find that KCs have numerous axo-axonic connections mediated by the muscarinic type-B receptor (mAChR-B). By using functional imaging and optogenetic approaches, we show that these axo-axonic connections suppress both odor-evoked calcium responses and dopamine-evoked cAMP signals in neighboring KCs. Strikingly, behavior experiments demonstrate that mAChR-B knockdown in KCs impairs olfactory learning by inducing undesired changes to the valence of an odor that was not associated with the reinforcer. Thus, this local neuromodulation acts in concert with sparse sensory representations and global dopaminergic modulation to achieve effective and accurate memory formation.

The organization and cellular composition of tissues are key determinants of their biological function. In the mammalian gastrointestinal (GI) tract, the enteric nervous system (ENS) intercalates between muscular and epithelial layers of the gut wall and can control GI function independent of central nervous system (CNS) input.1 As in the CNS, distinct regions of the GI tract are highly specialized and support diverse functions, yet the regional and spatial organization of the ENS remains poorly characterized.2 Cellular arrangements,3,4 circuit connectivity patterns,5,6 and diverse cell types7-9 are known to underpin ENS functional complexity and GI function, but enteric neurons are most typically described only as a uniform meshwork of interconnected ganglia. Here, we present a bird's eye view of the mouse ENS, describing its previously underappreciated cytoarchitecture and regional variation. We visually and computationally demonstrate that enteric neurons are organized in circumferential neuronal stripes. This organization emerges gradually during the perinatal period, with neuronal stripe formation in the small intestine (SI) preceding that in the colon. The width of neuronal stripes varies throughout the length of the GI tract, and distinct neuronal subtypes differentially populate specific regions of the GI tract, with stark contrasts between SI and colon as well as within subregions of each. This characterization provides a blueprint for future understanding of region-specific GI function and identifying ENS structural correlates of diverse GI disorders.

The movements of animal appendages are determined by extrinsic and intrinsic forces. Extrinsic forces include gravity or friction,1,2 whereas intrinsic forces are generated by active muscle contraction or passive musculoskeletal elements.3,4 For lightweight appendages, such as insect limbs, movements depend more upon intrinsic than extrinsic forces.5,6 Indeed, passive movements of insect limbs can be large and oppose or aid joint flexion, extension, or both.4 Yet, how passive properties contribute to insects' goal-directed limb movements, such as targeted reaching and searching,7-10 remains unclear. Here, we show that mantids make targeted reaches and searches to objects by using their raptorial forelimbs, employing braking to slow passive flexion of the femoro-tibial (FTi) joint. In most reaches, tibial flexion ensures the forelimb contacts the object. Such tibial flexion is particularly clear when the forelimb misses the object and continues on a downward trajectory or during directed searching movements. We characterize the passive properties of the FTi joint by combining passive movements of excised limbs with apodeme ablations and muscle stimulation. These experiments show that passive properties of the flexor tibiae muscle-apodeme complex are the primary structural element producing tibial flexion in excised limbs. During reaching and searching, however, tibial flexion is slower and smaller than predicted. This is due to braking, which opposes passive flexion, thereby reducing the magnitude and velocity of tibial flexion. Braking retarding passive movements is a novel behaviorally relevant control strategy for the goal-directed movements of lightweight limbs, such as those of insects.

Comment in Curr Biol. 2022 Oct 24;32(20):R1028-R1029.

Early-life microbial colonization is an important process shaping host physiology,1-3 immunity,4-6 and long-term health outcomes7-10 in humans. However, our understanding of this dynamic process remains poorly investigated in wild animals,11-13 where developmental mechanisms can be better understood within ecological and evolutionarily relevant contexts.11,12 Using one of the largest developmental datasets on a wild primate-the gelada (Theropithecus gelada)-we used 16S rRNA amplicon sequencing to characterize gut microbiota maturation during the first 3 years of life and assessed the role of maternal effects in shaping offspring microbiota assembly. In contrast to recent data on chimpanzees, postnatal microbial colonization in geladas was highly similar to humans:14 microbial alpha diversity increased rapidly following birth, followed by gradual changes in composition until weaning. Dietary changes associated with weaning (from milk- to plant-based diet) were the main drivers of shifts in taxonomic composition and microbial predicted functional pathways. Maternal effects were also an important factor influencing the offspring gut microbiota. During nursing (<12 months), offspring of experienced (multi-time) mothers exhibited faster functional microbial maturation, likely reflecting the general faster developmental pace of infants born to these mothers. Following weaning (>18 months), the composition of the juvenile microbiota tended to be more similar to the maternal microbiota than to the microbiota of other adult females, highlighting that maternal effects may persist even after nursing cessation.15,16 Together, our findings highlight the dynamic nature of early-life gut colonization and the role of maternal effects in shaping this trajectory in a wild primate.

Filopodia are narrow cell extensions involved in various physiological processes. Integrins mediate filopodia adhesion and likely transmit adhesive force to regulate filopodia formation and functions, but the force is extremely weak to study and remains poorly understood. Using integrative tension sensor (ITS), we imaged filopodia adhesive force at the single molecular tension level and investigated the force dynamics and sources. Results show that filopodia integrin tension (FIT) is generated in discrete foci (force nodes) along single filopodia with a spacing of ∼1 μm. Inhibitions of actin polymerization or myosin II activity markedly reduced FIT signals in force nodes at filopodia tips and at filopodia bases, respectively, suggesting differential force sources of FIT in the distal force nodes and proximal ones in filopodia. Using two ITS constructs with different force thresholds for activation, we showed that the molecular force level of FIT is greater at filopodia bases than that at filopodia tips. We also tested the role of vinculin and myosin X in the FIT transmission. With vinculin knockout in cells, filopodia and associated force nodes were still formed normally, suggesting that vinculin is dispensable for the formation of filopodia and force nodes. However, vinculin is indeed required for the transmission of strong FIT (capable of rupturing DNA in a shear conformation), as the strong FIT vanished in filopodia with vinculin knockout. Co-imaging of FIT and myosin X shows no apparent co-localization, demonstrating that myosin X is not directly responsible for generating FIT, despite its prominent role in filopodium elongation.

Apical-basal polarity is an essential epithelial trait controlled by the evolutionarily conserved PAR-aPKC polarity network. Dysregulation of polarity proteins disrupts tissue organization during development and in disease, but the underlying mechanisms are unclear due to the broad implications of polarity loss. Here, we uncover how Drosophila aPKC maintains epithelial architecture by directly observing tissue disorganization after fast optogenetic inactivation in living adult flies and ovaries cultured ex vivo. We show that fast aPKC perturbation in the proliferative follicular epithelium produces large epithelial gaps that result from increased apical constriction, rather than loss of apical-basal polarity. Accordingly, we can modulate the incidence of epithelial gaps by increasing and decreasing actomyosin-driven contractility. We traced the origin of these large epithelial gaps to tissue rupture next to dividing cells. Live imaging shows that aPKC perturbation induces apical constriction in non-mitotic cells within minutes, producing pulling forces that ultimately detach dividing and neighboring cells. We further demonstrate that epithelial rupture requires a global increase of apical constriction, as it is prevented by the presence of non-constricting cells. Conversely, a global induction of apical tension through light-induced recruitment of RhoGEF2 to the apical side is sufficient to produce tissue rupture. Hence, our work reveals that the roles of aPKC in polarity and actomyosin regulation are separable and provides the first in vivo evidence that excessive tissue stress can break the epithelial barrier during proliferation.

Survival requires both the ability to persistently pursue goals and the ability to determine when it is time to stop, an adaptive balance of perseverance and disengagement. Neural activity in the lateral habenula (LHb) has been linked to negative valence, but its role in regulating the balance between engaged reward seeking and disengaged behavioral states remains unclear. Here, we show that LHb neural activity is tonically elevated during minutes-long periods of disengagement from reward-seeking behavior, both when due to repeated reward omission (negative valence) and when sufficient reward has been consumed (positive valence). Furthermore, we show that LHb inhibition extends ongoing reward-seeking behavioral states but does not prompt task re-engagement. We find no evidence for similar tonic activity changes in ventral tegmental area dopamine neurons. Our findings support a framework in which tonic activity in LHb neurons suppresses engagement in reward-seeking behavior in response to both negatively and positively valenced factors.

Approximately 20%-30% of infants cry excessively and exhibit sleep difficulties for no apparent reason, causing parental stress and even triggering impulsive child maltreatment in a small number of cases.1-8 While several sleep training methods or parental education programs may provide long-term improvement of infant cry and sleep problems, there is yet to be a conclusive recommendation for on-site behavioral interventions.9-13 Previously we have reported that brief carrying of infants transiently reduces infant cry via the transport response, a coordinated set of vagal activation and behavioral calming conserved in altricial mammals.14-18 In this study, we disentangled complex infant responses to maternal holding and transport by combining subsecond-scale, event-locked physiological analyses with dynamic mother-infant interactions. Infant cry was attenuated either by maternal carrying or by reciprocal motion provided by a moving cot, but not by maternal holding. Five-minute carrying promoted sleep for crying infants even in the daytime when these infants were usually awake, but not for non-crying infants. Maternal laydown of sleeping infants into a cot exerted bimodal effects, either interrupting or deepening the infants' sleep. During laydown, sleeping infants were alerted most consistently by the initiation of maternal detachment, then calmed after the completion of maternal detachment in a successful laydown. Finally, the sleep outcome after laydown was associated with the sleep duration before the laydown onset. These data propose a "5-min carrying, 5- to 8- min sitting" scheme for attending to infant cry and sleep difficulties, which should be further substantiated in future studies. VIDEO ABSTRACT.

Supergenes govern multi-trait-balanced polymorphisms in a wide range of systems; however, our understanding of their origins and evolution remains incomplete. The reciprocal placement of stigmas and anthers in pin and thrum floral morphs of distylous species constitutes an iconic example of a balanced polymorphism governed by a supergene, the distyly S-locus. Recent studies have shown that the Primula and Turnera distyly supergenes are both hemizygous in thrums, but it remains unknown whether hemizygosity is pervasive among distyly S-loci. As hemizygosity has major consequences for supergene evolution and loss, clarifying whether this genetic architecture is shared among distylous species is critical. Here, we have characterized the genetic architecture and evolution of the distyly supergene in Linum by generating a chromosome-level genome assembly of Linum tenue, followed by the identification of the S-locus using population genomic data. We show that hemizygosity and thrum-specific expression of S-linked genes, including a pistil-expressed candidate gene for style length, are major features of the Linum S-locus. Structural variation is likely instrumental for recombination suppression, and although the non-recombining dominant haplotype has accumulated transposable elements, S-linked genes are not under relaxed purifying selection. Our findings reveal remarkable convergence in the genetic architecture and evolution of independently derived distyly supergenes, provide a counterexample to classic inversion-based supergenes, and shed new light on the origin and maintenance of an iconic floral polymorphism.

Root systems regulate their branching patterns in response to environmental stimuli. Lateral root development in both monocotyledons and dicotyledons is enhanced in response to inoculation with arbuscular mycorrhizal (AM) fungi, which has been interpreted as a developmental response to specific, symbiosis-activating chitinaceous signals. Here, we report that generic instead of symbiosis-specific, chitin-derived molecules trigger lateral root formation. We demonstrate that this developmental response requires the well-known microbe-associated molecular pattern (MAMP) receptor, Chitin Elicitor Receptor Kinase 1 (CERK1), in rice, Medicago truncatula, and Lotus japonicus, as well as the non-host of AM fungi, Arabidopsis thaliana, lending further support for a broadly conserved signal transduction mechanism across angiosperms. Using rice mutants impaired in strigolactone biosynthesis and signaling, we show that strigolactone signaling is necessary to regulate this developmental response. Rice CERK1 operates together with either Chitin Elicitor Binding Protein (CEBiP) or Nod Factor Receptor 5 (NFR5) in immunity and symbiosis signaling, respectively; for the lateral root response, however, all three LysM receptors are required. Our work, therefore, reveals an overlooked but a conserved role of LysM receptors integrating MAMP perception with developmental responses in plants, an ability that might influence the interaction between roots and the rhizosphere biota.

Sexual selection is the basis of some of the most striking phenotypic variation in nature.1,2 In animals, sexual selection in males can act on traits that improve access to mates prior to copulation,3-8 but also on sperm traits filtered by sperm competition,9-14 or female choice expressed simply by the morphology and physiology of genital tracts.14-16 Although long overlooked as a mode of selection on plant traits, sexual selection should act on land plants too because they are anisogamous: males produce more, and smaller, gametes than females.17-19 Numerical asymmetry in gamete production is thought to play a central role in selection on traits that affect pollen transfer to mates,20,21 but very little is known about how pollen competition or cryptic female choice might affect the evolution of traits expressed after pollination.22,23 Here, we report the divergence of pollen and pistil traits of the dioecious wind-pollinated annual herb Mercurialis annua during evolution over three generations between populations at low versus high plant density, corresponding to low versus higher levels of polyandry;24 we expected selection under higher polyandry to strengthen competition among pollen donors for fertilizing ovules. We found that populations at high density evolved faster-growing pollen tubes (an equivalent of greater sperm velocity), greater expression of pollen proteins involved in pollen growth, and larger stigmas (a trait likely enhancing the number of pollen donors and thus competition for ovules). Our results identify the post-pollination phase of plant mating as an important arena for the action of sexual selection.

Comment in Curr Biol. 2022 Oct 24;32(20):R1030-R1032.

The effect of the detailed connectivity of a neural circuit on its function and the resulting behavior of the organism is a key question in many neural systems. Here, we study the circuit for nociception in C. elegans, which is composed of the same neurons in the two sexes that are wired differently. We show that the nociceptive sensory neurons respond similarly in the two sexes, yet the animals display sexually dimorphic behaviors to the same aversive stimuli. To uncover the role of the downstream network topology in shaping behavior, we learn and simulate network models that replicate the observed dimorphic behaviors and use them to predict simple network rewirings that would switch behavior between the sexes. We then show experimentally that these subtle synaptic rewirings indeed flip behavior. Interestingly, when presented with aversive cues, rewired males were compromised in finding mating partners, suggesting that network topologies that enable efficient avoidance of noxious cues have a reproductive "cost." Our results present a deconstruction of the design of a neural circuit that controls sexual behavior and how to reprogram it.

Interview with Yoselin Benitez-Alfonso, who studies cell-to-cell signalling in plants.

Comment on Curr Biol. 2022 Oct 10;32(19):4114-4127.e6.

Comment in Curr Biol. 2022 Oct 10;32(19):R1005-R1007.

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Comment on Curr Biol. 2022 Oct 10;32(19):4201-4214.e12.

Temperatures outside the preferred range require flies to acutely adjust their behavior. A new study finds that heat-sensing neurons provide input to fly circadian clock neurons to extend the daytime siesta, allowing flies to sleep through excessive daytime heat.

Comment on Curr Biol. 2022 Oct 10;32(19):4159-4171.e9.

How does tissue elongation occur? A recent paper identifies a new mechanism: elongation of the Caenorhabditis elegans hermaphrodite gonad is driven by pressure from proliferating germ cells confined within a tube. The distal tip cell, which caps the tube, remodels the extracellular matrix and adjusts cell-matrix adhesion to guide the way.

Comment on Curr Biol. 2022 Oct 10;32(19):4255-4263.e5.

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Comment in Curr Biol. 2022 Oct 10;32(19):R1015-R1018.

Prosocial behaviors-actions that benefit others-are central to individual and societal well-being. Although the mechanisms underlying the financial and moral costs of prosocial behaviors are increasingly understood, this work has often ignored a key influence on behavior: effort. Many prosocial acts are effortful, and people are averse to the costs of exerting them. However, how the brain encodes effort costs when actions benefit others is unknown. During fMRI, participants completed a decision-making task where they chose in each trial whether to "work" and exert force (30%-70% of maximum grip strength) or "rest" (no effort) for rewards (2-10 credits). Crucially, on separate trials, they made these decisions either to benefit another person or themselves. We used a combination of multivariate representational similarity analysis and model-based univariate analysis to reveal how the costs of prosocial and self-benefiting efforts are processed. Strikingly, we identified a unique neural signature of effort in the anterior cingulate gyrus (ACCg) for prosocial acts, both when choosing to help others and when exerting force to benefit them. This pattern was absent for self-benefiting behaviors. Moreover, stronger, specific representations of prosocial effort in the ACCg were linked to higher levels of empathy and higher subsequent exerted force to benefit others. In contrast, the ventral tegmental area and ventral insula represented value preferentially when choosing for oneself and not for prosocial acts. These findings advance our understanding of the neural mechanisms of prosocial behavior, highlighting the critical role that effort has in the brain circuits that guide helping others.

Comment on Curr Biol. 2022 Oct 10;32(19):4215-4224.e3.

Warming seas, marine heatwaves, and habitat degradation are increasingly widespread phenomena affecting marine biodiversity, yet our understanding of their broader impacts is largely derived from collective insights from independent localized studies. Insufficient systematic broadscale monitoring limits our understanding of the true extent of these impacts and our capacity to track these at scales relevant to national policies and international agreements. Using an extensive time series of co-located reef fish community structure and habitat data spanning 12 years and the entire Australian continent, we found that reef fish community responses to changing temperatures and habitats are dynamic and widespread but regionally patchy. Shifts in composition and abundance of the fish community often occurred within 2 years of environmental or habitat change, although the relative importance of these two mechanisms of climate impact tended to differ between tropical and temperate zones. The clearest of these changes on temperate and subtropical reefs were temperature related, with responses measured by the reef fish thermal index indicating reshuffling according to the thermal affinities of species present. On low latitude coral reefs, the community generalization index indicated shifting dominance of habitat generalist fishes through time, concurrent with changing coral cover. Our results emphasize the importance of maintaining local ecological detail when scaling up datasets to inform national policies and global biodiversity targets. Scaled-up ecological monitoring is needed to discriminate among increasingly diverse drivers of large-scale biodiversity change and better connect presently disjointed systems of biodiversity observation, indicator research, and governance.

Comment in Curr Biol. 2022 Oct 10;32(19):R1010-R1012.

Brains are among the most energetically costly tissues in the mammalian body.1 This is predominantly caused by expensive neurons with high glucose demands.2 Across mammals, the neuronal energy budget appears to be fixed, possibly posing an evolutionary constraint on brain growth.3-6 Compared to similarly sized mammals, birds have higher numbers of neurons, and this advantage conceivably contributes to their cognitive prowess.7 We set out to determine the neuronal energy budget of birds to elucidate how they can metabolically support such high numbers of neurons. We estimated glucose metabolism using positron emission tomography (PET) and 2-[18F]fluoro-2-deoxyglucose ([18F]FDG) as the radiotracer in awake and anesthetized pigeons. Combined with kinetic modeling, this is the gold standard to quantify cerebral metabolic rate of glucose consumption (CMRglc).8 We found that neural tissue in the pigeon consumes 27.29 ± 1.57 μmol glucose per 100 g per min in an awake state, which translates into a surprisingly low neuronal energy budget of 1.86 × 10-9 ± 0.2 × 10-9 μmol glucose per neuron per minute. This is approximately 3 times lower than the rate in the average mammalian neuron.3 The remarkably low neuronal energy budget explains how pigeons, and possibly other avian species, can support such high numbers of neurons without associated metabolic costs or compromising neuronal signaling. The advantage in neuronal processing of information at a higher efficiency possibly emerged during the distinct evolution of the avian brain.

Does perceptual awareness arise within the sensory regions of the brain or within higher-level regions (e.g., the frontal lobe)? To answer this question, researchers traditionally compare neural activity when observers report being aware versus being unaware of a stimulus. However, it is unclear whether the resulting activations are associated with the conscious perception of the stimulus or the post-perceptual processes associated with reporting that stimulus. To address this limitation, we used both report and no-report conditions in a visual masking paradigm while participants were scanned using functional MRI (fMRI). We found that the overall univariate response to visible stimuli in the frontal lobe was robust in the report condition but disappeared in the no-report condition. However, using multivariate patterns, we could still decode in both conditions whether a stimulus reached conscious awareness across the brain, including in the frontal lobe. These results help reconcile key discrepancies in the recent literature and provide a path forward for identifying the neural mechanisms associated with perceptual awareness.

The diversity of visual input processed by the mammalian visual system requires the generation of many distinct retinal ganglion cell (RGC) types, each tuned to a particular feature. The molecular code needed to generate this cell-type diversity is poorly understood. Here, we focus on the molecules needed to specify one type of retinal cell: the upward-preferring ON direction-selective ganglion cell (up-oDSGC) of the mouse visual system. Single-cell transcriptomic profiling of up- and down-oDSGCs shows that the transcription factor Tbx5 is selectively expressed in up-oDSGCs. The loss of Tbx5 in up-oDSGCs results in a selective defect in the formation of up-oDSGCs and a corresponding inability to detect vertical motion. A downstream effector of Tbx5, Sfrp1, is also critical for vertical motion detection but not up-oDSGC formation. These results advance our understanding of the molecular mechanisms that specify a rare retinal cell type and show how disrupting this specification leads to a corresponding defect in neural circuitry and behavior.

Early embryo development requires maternal-to-zygotic transition, during which transcriptionally silent nuclei begin widespread gene expression during zygotic genome activation (ZGA).1-3 ZGA is vital for early cell fating and germ-layer specification,3,4 and ZGA timing is regulated by multiple mechanisms.1-5 However, controversies remain about whether these mechanisms are interrelated and vary among species6-10 and whether the timing of germ-layer-specific gene activation is temporally ordered.11,12 In some embryonic models, widespread ZGA onset is spatiotemporally graded,13,14 yet it is unclear whether the transcriptome follows this pattern. A major challenge in addressing these questions is to accurately measure the timing of each gene activation. Here, we metabolically label and identify the nascent transcriptome using 5-ethynyl uridine (5-EU) in Xenopus blastula embryos. We find that EU-RNA-seq outperforms total RNA-seq in detecting the ZGA transcriptome, which is dominated by transcription from maternal-zygotic genes, enabling improved ZGA timing determination. We uncover discrete spatiotemporal patterns for individual gene activation, a majority following a spatial pattern of ZGA that is correlated with a cell size gradient.14 We further reveal that transcription necessitates a period of developmental progression and that ZGA can be precociously induced by cycloheximide, potentially through elongation of interphase. Finally, most ectodermal genes are activated earlier than endodermal genes, suggesting a temporal orchestration of germ-layer-specific genes, potentially linked to the spatially graded pattern of ZGA. Together, our study provides fundamental new insights into the composition and dynamics of the ZGA transcriptome, mechanisms regulating ZGA timing, and its role in the onset of early cell fating.

Sensory receptors evolve, and changes to their response profiles can directly impact sensory perception and affect diverse behaviors, from mate choice to foraging decisions.1-3 Although receptor sensitivities can be highly contingent on changes occurring early in a lineage's evolutionary history,4 subsequent shifts in a species' behavior and ecology may exert selective pressure to modify and even reverse sensory receptor capabilities.5-7 Neither the extent to which sensory reversion occurs nor the mechanisms underlying such shifts is well understood. Using receptor profiling and behavioral tests, we uncover both an early gain and an unexpected subsequent loss of sugar sensing in woodpeckers, a primarily insectivorous family of landbirds.8,9 Our analyses show that, similar to hummingbirds10 and songbirds,4 the ancestors of woodpeckers repurposed their T1R1-T1R3 savory receptor to detect sugars. Importantly, whereas woodpeckers seem to have broadly retained this ability, our experiments demonstrate that wrynecks (an enigmatic ant-eating group sister to all other woodpeckers) selectively lost sugar sensing through a novel mechanism involving a single amino acid change in the T1R3 transmembrane domain. The identification of this molecular microswitch responsible for a sensory shift in taste receptors provides an example of the molecular basis of a sensory reversion in vertebrates and offers novel insights into structure-function relationships during sensory receptor evolution.

Comment in Curr Biol. 2022 Nov 7;32(21):R1240-R1242.

Comment in Curr Biol. 2022 Oct 10;32(19):R998-R1000.

A key component of nature's contribution to people is aesthetic value.1,2 Charismatic species rally public support and bolster conservation efforts.3,4 However, an insidious aspect to humanity's valuation of nature is that high value also drives wildlife trade,5,6 which can spearhead the demise of prized species.7-9 Here, we explore the antagonistic roles of aesthetic value in biodiversity conservation by using novel metrics of color to evaluate the aesthetics of the most speciose radiation of birds: passerines (i.e., the perching birds). We identify global color hotspots for passerines and highlight the breadth of color in the global bird trade. The tropics emerge as an epicentre of color, encompassing 91% and 65% of the world's most diverse and most uniquely colored passerine assemblages, respectively. We show that the pet trade, which currently affects 30% of passerines (1,408/5,266), traverses the avian phylogeny and targets clusters of related species that are uniquely colored. We identify an additional 478 species at risk of future trade based on their coloration and phylogenetic relationship to currently traded species-together totaling 1,886 species traded, a 34% increase. By modeling future extinctions based on species' current threat status, we predict localized losses of color diversity and uniqueness in many avian communities, undermining their aesthetic value and muting nature's color palette. Given the distribution of color and the association of unique colors with threat and trade, proactive regulation of the bird trade is crucial to conserving charismatic biodiversity, alongside recognition and celebration of color hotspots.

Chromosome alignment to the spindle equator is a hallmark of mitosis thought to promote chromosome segregation fidelity in metazoans. Yet chromosome alignment is only indirectly supervised by the spindle assembly checkpoint (SAC) as a byproduct of chromosome bi-orientation, and the consequences of defective chromosome alignment remain unclear. Here, we investigated how human cells respond to chromosome alignment defects of distinct molecular nature by following the fate of live HeLa cells after RNAi-mediated depletion of 125 proteins previously implicated in chromosome alignment. We confirmed chromosome alignment defects upon depletion of 108/125 proteins. Surprisingly, in all confirmed cases, depleted cells frequently entered anaphase after a delay with misaligned chromosomes. Using depletion of prototype proteins resulting in defective chromosome alignment, we show that misaligned chromosomes often satisfy the SAC and directly missegregate without lagging behind in anaphase. In-depth analysis of specific molecular perturbations that prevent proper kinetochore-microtubule attachments revealed that misaligned chromosomes that missegregate frequently result in micronuclei. Higher-resolution live-cell imaging indicated that, contrary to most anaphase lagging chromosomes that correct and reintegrate the main nuclei, misaligned chromosomes are a strong predictor of micronuclei formation in a cancer cell model of chromosomal instability, but not in non-transformed near-diploid cells. We provide evidence supporting that intrinsic differences in kinetochore-microtubule attachment stability on misaligned chromosomes account for this distinct outcome. Thus, misaligned chromosomes that satisfy the SAC may represent a previously overlooked mechanism driving chromosomal/genomic instability during cancer cell division, and we unveil genetic conditions predisposing for these events.

Bacteria require membrane fission for both cell division and endospore formation. In Bacillus subtilis, sporulation initiates with an asymmetric division that generates a large mother cell and a smaller forespore that contains only a quarter of its genome. As the mother cell membranes engulf the forespore, a DNA translocase pumps the rest of the chromosome into the small forespore compartment, inflating it due to increased turgor. When the engulfing membrane undergoes fission, the forespore is released into the mother cell cytoplasm. The B. subtilis protein FisB catalyzes membrane fission during sporulation, but the molecular basis is unclear. Here, we show that forespore inflation and FisB accumulation are both required for an efficient membrane fission. Forespore inflation leads to higher membrane tension in the engulfment membrane than in the mother cell membrane, causing the membrane to flow through the neck connecting the two membrane compartments. Thus, the mother cell supplies some of the membrane required for the growth of the membranes surrounding the forespore. The oligomerization of FisB at the membrane neck slows the equilibration of membrane tension by impeding the membrane flow. This leads to a further increase in the tension of the engulfment membrane, promoting its fission through lysis. Collectively, our data indicate that DNA translocation has a previously unappreciated second function in energizing the FisB-mediated membrane fission under energy-limited conditions.

Comment in Curr Biol. 2022 Oct 10;32(19):R1018-R1020.

Comment in Curr Biol. 2022 Oct 10;32(19):R1002-R1005.

Comment in Curr Biol. 2022 Oct 10;32(19):R1012-R1015.

Comment in Curr Biol. 2022 Oct 10;32(19):R1000-R1002.

Elevated sugar consumption is associated with an increased risk for metabolic diseases. Whereas evidence from humans, rodents, and insects suggests that dietary sucrose modifies sweet taste sensation, understanding of peripheral nerve or taste bud alterations is sparse. To address this, male rats were given access to 30% liquid sucrose for 4 weeks (sucrose rats). Neurophysiological responses of the chorda tympani (CT) nerve to lingual stimulation with sugars, other taste qualities, touch, and cold were then compared with controls (access to water only). Morphological and immunohistochemical analyses of fungiform papillae and taste buds were also conducted. Sucrose rats had substantially decreased CT responses to 0.15-2.0 M sucrose compared with controls. In contrast, effects were not observed for glucose, fructose, maltose, Na saccharin, NaCl, organic acid, or umami, touch, or cold stimuli. Whereas taste bud number, size, and innervation volume were unaffected, the number of PLCβ2+ taste bud cells in the fungiform papilla was reduced in sucrose rats. Notably, the replacement of sucrose with water resulted in a complete recovery of all phenotypes over 4 weeks. The work reveals the selective and modality-specific effects of sucrose consumption on peripheral taste nerve responses and taste bud cells, with implications for nutrition and metabolic disease risk. VIDEO ABSTRACT.

Stephanie Sarbanes et al. discuss microtubule-severing enzymes, highlighting their shared structure and mechanism and the diversity of processes in which they participate.