Comment on Curr Biol. 2021 Mar 8;31(5):1084-1091.e4.

Comment on Curr Biol. 2021 Mar 8;31(5):911-922.e4. Curr Biol. 2021 Mar 8;31(5):923-935.e11.

Our understanding of the earliest evolution of jawed vertebrates depends on a credible phylogenetic framework for the jawed stem gnathostomes collectively known as "placoderms".1 However, their relationships, and whether placoderms represent a single radiation or a paraphyletic array, remain contentious.2-13 This uncertainty is compounded by an uneven understanding of anatomy across the group, particularly of the phylogenetically informative braincase and brain cavity-endocast. Based on new tomographic data, we here describe the endocast and bony labyrinth of Brindabellaspis stensioi from the Early Devonian of New South Wales.14 The taxon was commonly recovered as branching near the base of placoderms.5-9,11,12,15-17 Previous studies of Brindabellaspis emphasized its resemblances with fossil jawless fishes in the braincase anatomy14 and endocast proportions1,18 and its distinctive features were interpreted as autapomorphies, such as the elongated premedian region.19 Although our three-dimensional data confirmed the resemblance of its endocast to those of jawless vertebrates, we discovered that the inner ear and endolymphatic complex display a repertoire of previously unrecognized characters close to modern or crown-group jawed vertebrates, including a pronounced sinus superior and a vertical duct that connects the endolymphatic sac and the labyrinth cavity. Both parsimony and Bayesian analyses suggest that prevailing hypotheses of placoderm relationships are unstable, with newly revealed anatomy pointing to a radical revision of early gnathostome evolution. Our results call into question the appropriateness of arthrodire-like placoderms as models of primitive gnathostome anatomy and raise questions of homology relating to key cranial features.

Comment in Curr Biol. 2021 Mar 8;31(5):R241-R243.

Analysis of single-cell measurements of bacterial growth and division often relied on testing preconceived models of cell size control mechanisms. Such an approach could limit the scope of data analysis and prevent us from uncovering new information. Here, we take an "agnostic" approach by applying regression methods to multiple simultaneously measured cellular variables, which allow us to infer dependencies among those variables from their apparent correlations. Besides previously observed correlations attributed to particular cell size control mechanisms, we identify dependencies that point to potentially new mechanisms. In particular, cells born smaller than their sisters tend to grow faster and make up for the size difference acquired during division. We also find that sister cells are correlated beyond what single-cell, size-control models predict. These trends are consistently found in repeat experiments, although the dependencies vary quantitatively. Such variation highlights the sensitivity of cell growth to environmental variations and the limitation of currently used experimental setups.

Since antiquity, the term 'imitation' has been used promiscuously in biology and everyday life. Anything that makes some individuals look or act like others has been called imitation, from the evolutionary process that makes edible butterflies look like their inedible cousins (better known as Batesian mimicry), to the rag-bag of psychological processes that make people wear similar clothes, eat in the same restaurants, and use the same gestures for communication.

Dima and Inzé discuss how Europe is lagging behind in embracing the potential of genome editing in crops and highlight how scientists can contribute to advising on effective science-based policies for more sustainable agriculture through genome editing.

Episodic memory retrieval is thought to rely on reactivation of the same content-sensitive neural activity patterns initially expressed during memory encoding.1-6 Yet there are emerging examples of content representations expressed in different brain regions during encoding versus retrieval.7-14 Although these differences have been observed by comparing encoding and retrieval tasks that differ in terms of perceptual experience and cognitive demands, there are many real-world contexts-e.g., meeting a new colleague who reminds you of an old acquaintance-where the memory system might be intrinsically biased either toward encoding (the new colleague) or retrieval (the old acquaintance).1516 Here, we test whether intrinsic memory states, independent of task demands, determine the cortical location of content representations. In a human fMRI study, subjects (n = 33) viewed object images and were instructed to either encode the current object or retrieve a similar object from memory. Using pattern classifiers, we show that biases toward encoding versus retrieval were reflected in large-scale attentional networks.17-19 Critically, memory states decoded from these networks-even when entirely independent from task instructions-predicted shifts of object representations from visual cortex (encoding) to ventral parietal cortex (retrieval). Finally, visual versus ventral parietal cortices exhibited differential connectivity with the hippocampus during memory encoding versus retrieval, consistent with the idea that the hippocampus mediates cortical shifts in content representations. Collectively, these findings demonstrate that intrinsic biases toward memory encoding versus retrieval determine the specific cortical locations that express content information.

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Comment in Curr Biol. 2021 Mar 8;31(5):R246-R248.

The transition from the Late Neolithic to the Bronze Age has witnessed important population and societal changes in western Europe.1 These include massive genomic contributions of pastoralist herders originating from the Pontic-Caspian steppes2,3 into local populations, resulting from complex interactions between collapsing hunter-gatherers and expanding farmers of Anatolian ancestry.4-8 This transition is documented through extensive ancient genomic data from present-day Britain,9,10 Ireland,11,12 Iberia,13 Mediterranean islands,14,15 and Germany.8 It remains, however, largely overlooked in France, where most focus has been on the Middle Neolithic (n = 63),8,9,16 with the exception of one Late Neolithic genome sequenced at 0.05× coverage.16 This leaves the key transitional period covering ∼3,400-2,700 cal. years (calibrated years) BCE genetically unsampled and thus the exact time frame of hunter-gatherer persistence and arrival of steppe migrations unknown. To remediate this, we sequenced 24 ancient human genomes from France spanning ∼3,400-1,600 cal. years BCE. This reveals Late Neolithic populations that are genetically diverse and include individuals with dark skin, hair, and eyes. We detect heterogeneous hunter-gatherer ancestries within Late Neolithic communities, reaching up to ∼63.3% in some individuals, and variable genetic contributions of steppe herders in Bell Beaker populations. We provide an estimate as late as ∼3,800 years BCE for the admixture between Neolithic and Mesolithic populations and as early as ∼2,650 years BCE for the arrival of steppe-related ancestry. The genomic heterogeneity characterized underlines the complex history of human interactions even at the local scale.

One of the main reasons why amputees report poor satisfaction with prostheses is their excessive weight perceived,1 despite the fact that they typically weigh less than half of the natural limb.2 Weight perception can be a subjective percept that is influenced by cognitive processes.3-5 Even though recent developments in prosthetics have shown that sensory feedback restoration positively influences cognitive aspects (as embodiment of the device and cognitive load),6,7 the potential benefits on prosthesis heaviness perception have never been investigated. In this study, we explored this matter using intraneural sensory feedback in a transfemoral (above-knee) amputee. We hypothesized that providing neural feedback would affect the integration of the prosthesis in the amputee's body schema, hence influencing the prosthesis weight perception. The results indicate that, after performing an over-ground walking task, the sensory feedback allowed a 23% decrease in prosthesis heaviness perception compared to the no feedback condition. Our hypothesis was confirmed by a significant increase in the embodiment of the prosthesis (by 60.5%) and confidence (by 36%) while walking with the sensory feedback. A subsequent dual task (i.e., walking while spelling backward) showed that the sensory feedback abolished the reduction of walking speed and accuracy observed during the no-feedback condition and normally seen with increased mental workload, suggesting a cognitive integration of the system. These results show the importance of providing close-to-natural sensations from the missing limb to allow a good integration of the prostheses and increase the satisfaction of their users. VIDEO ABSTRACT.

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Comment in Curr Biol. 2021 Mar 8;31(5):R260-R263.

Honeybees1 and bumblebees2 perform learning flights when leaving a newly discovered flower. During these flights, bees spend a portion of the time turning back to face the flower when they can memorize views of the flower and its surroundings. In honeybees, learning flights become longer when the reward offered by a flower is increased.3 We show here that bumblebees behave in a similar way, and we add that bumblebees face an artificial flower more when the concentration of the sucrose solution that the flower provides is higher. The surprising finding is that a bee's size determines what a bumblebee regards as a "low" or "high" concentration and so affects its learning behavior. The larger bees in a sample of foragers only enhance their flower facing when the sucrose concentration is in the upper range of the flowers that are naturally available to bees.4 In contrast, smaller bees invest the same effort in facing flowers whether the concentration is high or low, but their effort is less than that of larger bees. The way in which different-sized bees distribute their effort when learning about flowers parallels the foraging behavior of a colony. Large bumblebees5,6 are able to carry larger loads and explore further from the nest than smaller ones.7 Small ones with a smaller flight range and carrying capacity cannot afford to be as selective and so accept a wider range of flowers. VIDEO ABSTRACT.

Listeria monocytogenes is a foodborne bacterial pathogen that causes human listeriosis, a severe systemic infection.1 Its translocation across the intestinal epithelium is mediated by the interaction of internalin (InlA), a Listeria surface protein, with its host-species-specific receptor E-cadherin (Ecad).2-5 It occurs through goblet cells, on which Ecad is luminally accessible,6 via an unknown mechanism. In the absence of cell lines recapitulating this phenotype in vitro, we developed an ex vivo experimental system, based on the intraluminal microinjection of Listeria in untreated, pharmacologically treated, and genetically modified intestinal organoids. Using both live light-sheet microscopy and confocal imaging, we show that Listeria translocates through goblet cells within a membrane vacuole in an InlA- and microtubule-dependent manner. As Ecad undergoes constant apical-basal recycling,7,8 we hypothesized that Lm may transit through goblet cells by hijacking Ecad recycling pathway. Indeed, Listeria is stuck at goblet cell apex when Ecad endocytosis is blocked and remains trapped intracellularly at the basolateral pole of goblet cells when Rab11-dependent Ecad recycling is compromised. Together, these results show that Listeria, upon docking onto its luminally accessible receptor Ecad, hijacks its recycling pathway to be transferred by transcytosis across goblet cells. Live imaging of host-pathogen interactions in organoids is a promising approach to dissect their underlying cell and molecular biology.

How do we estimate the position of an object in the world around us? Naturally, we would direct our gaze to that object. Accordingly, neural motor coordinates entail the distance of external objects and thus might be used to derive perceptual estimates. Several general frameworks in the history of perceptual science have offered such a view.1-4 However, a mechanism showing how motor and visual processes communicate remains elusive. Here, we report that every post-saccadic error biases visual localization in a serially dependent manner. In order to simulate a realignment of visual space through motor coordinates, we induced an artificial de-alignment between visual and motor space. We found that when performing saccades under this distortion, post-saccadic error information clearly realigned visual and motor space, again in a serially dependent manner. These results demonstrate that the consequences of every saccade directly influence where we see objects in the world. On a neural basis, this requires that motor signals, which generate close to the saccade production machinery, are reported to cortical areas and arrange visual space. This view is consistent with recent electrophysiological findings of post-saccadic error processing in posterior parietal cortex.5.

Comment in Curr Biol. 2021 Mar 8;31(5):R243-R246.

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Comment on Curr Biol. 2021 Mar 8;31(5):978-989.e4.

Erratum in Curr Biol. 2021 Apr 26;31(8):1811.

Comment on Curr Biol. 2021 Mar 8;31(5):1092-1098.e6.

Comment on Curr Biol. 2021 Mar 8;31(5):1002-1011.e9.

It is a well-established fact that different tissues within the body contain their own circadian clocks or pacemakers, where it is proposed that the clock controls the local, daily cell biology of that organ.1,2 In mammals, these peripheral clocks work in concert with and are entrained by rhythmic signals arising from the suprachiasmatic nucleus (SCN) in the hypothalamus of the animal, among other systemic cues.2 In the case of zebrafish, the circadian system appears to be highly decentralized with each tissue not only having an internal circadian clock, but also being directly light entrained.1 Several years ago, we showed that the zebrafish heart contains its own circadian pacemaker at the gene expression level.1 This is also the case in mammals, where the circadian clock controls approximately 10% of the genes expressed in the heart.3 However, heart rate itself is generally thought to be regulated by several well-described autonomic cues, neurotransmitters, and hormones. In this study, we report that, for larval zebrafish hearts, the daily change in heartbeat rate is not only clock-controlled in vivo, but that this rhythm also persists in vitro, indicating that the cardiac circadian clock itself can directly drive this major physiological oscillation.

Antarctic krill (Euphausia superba, hereafter 'krill') exemplify the methodological challenges of studying small, mobile, aggregating pelagic organisms.1 Krill are a central species in the Southern Ocean food web, provide important biogeochemical functions and support a valuable commercial fishery.2 Most of what we know about krill has been derived from acoustic surveys and net samples, the former being essential for estimating krill biomass and catch limits. However, understanding krill behavior, particularly in the poorly-studied autumn-winter seasons, is key for management and conservation. Here, we used seasonal video observations collected with a profiling camera system of krill along the Western Antarctic Peninsula to reveal krill vertical distribution, aggregation density and individual behaviors that have remained hidden from traditional sampling methods.3.

Autotomy, the voluntary shedding of a body part, is common to distantly-related animals such as arthropods, gastropods, asteroids, amphibians, and lizards1,2. Autotomy is generally followed by regeneration of shed terminal body parts, such as appendages or tails. Here, we identify a new type of extreme autotomy in two species of sacoglossan sea slug (Mollusca: Gastropoda). Surprisingly, they shed the main body, including the whole heart, and regenerated a new body. In contrast, the shed body did not regenerate the head. These sacoglossans can incorporate chloroplasts from algal food into their cells to utilise for photosynthesis (kleptoplasty3), and we propose that this unique characteristic may facilitate survival after autotomy and subsequent regeneration.

Interview with Erin Goley, who studies the mechanisms governing bacterial morphogenesis and the regulation of bacterial growth in changing environments at Johns Hopkins University School of Medicine.

Comment in Curr Biol. 2021 Mar 8;31(5):R243-R246.

Plants restrict immune responses to vulnerable root parts. Spatially restricted responses are thought to be necessary to avoid constitutive responses to rhizosphere microbiota. To directly demonstrate the importance of spatially restricted responses, we expressed the plant flagellin receptor (FLS2) in different tissues, combined with fluorescent defense markers for immune readouts at cellular resolution. Our analysis distinguishes responses appearing cell autonomous from apparently non-cell-autonomous responses. It reveals lignification as a general immune response, contrasting suberization. Importantly, our analysis divides the root meristem into a central zone refractory to FLS2 expression and a cortex that is sensitized by FLS2 expression, causing meristem collapse upon stimulation. Meristematic epidermal expression generates super-competent lines that detect native bacterial flagellin and bypass the weak or absent response to commensals, providing a powerful tool for studying root immunity. Our manipulations and readouts demonstrate incompatibility of meristematic activity and defense and the importance of cell-resolved studies of plant immune responses.

A critical mechanism for maximizing reward is instrumental learning. In standard instrumental learning models, action values are updated on the basis of reward prediction errors (RPEs), defined as the discrepancy between expectations and outcomes. A wealth of evidence across species and experimental techniques has established that RPEs are signaled by midbrain dopamine neurons. However, the way dopamine neurons receive information about reward outcomes remains poorly understood. Recent animal studies suggest that the pedunculopontine nucleus (PPN), a small brainstem structure considered as a locomotor center, is sensitive to reward and sends excitatory projection to dopaminergic nuclei. Here, we examined the hypothesis that the PPN could contribute to reward learning in humans. To this aim, we leveraged a clinical protocol that assessed the therapeutic impact of PPN deep-brain stimulation (DBS) in three patients with Parkinson disease. PPN local field potentials (LFPs), recorded while patients performed an instrumental learning task, showed a specific response to reward outcomes in a low-frequency (alpha-beta) band. Moreover, PPN DBS selectively improved learning from rewards but not from punishments, a pattern that is typically observed following dopaminergic treatment. Computational analyses indicated that the effect of PPN DBS on instrumental learning was best captured by an increase in subjective reward sensitivity. Taken together, these results support a causal role for PPN-mediated reward signals in human instrumental learning.

Anomalous trichromacy is a common form of congenital color deficiency resulting from a genetic alteration in the photopigments of the eye's light receptors. The changes reduce sensitivity to reddish and greenish hues, yet previous work suggests that these observers may experience the world to be more colorful than their altered receptor sensitivities would predict, potentially indicating an amplification of post-receptoral signals. However, past evidence suggesting such a gain adjustment rests on subjective measures of color appearance or salience. We directly tested for neural amplification by using fMRI to measure cortical responses in color-anomalous and normal control observers. Color contrast response functions were measured in two experiments with different tasks to control for attentional factors. Both experiments showed a predictable reduction in chromatic responses for anomalous trichromats in primary visual cortex. However, in later areas V2v and V3v, chromatic responses in the two groups were indistinguishable. Our results provide direct evidence for neural plasticity that compensates for the deficiency in the initial receptor color signals and suggest that the site of this compensation is in early visual cortex.

Comment on Curr Biol. 2021 Mar 8;31(5):990-1001.e5.

Comment on Curr Biol. 2021 Mar 8;31(5):1099-1106.e5.

The encoding of light increments and decrements by separate On- and Off- systems is a fundamental ingredient of vision, which supports edge detection and makes efficient use of the limited dynamic range of visual neurons1. Theory predicts that the neural representation of On- and Off-signals should be balanced, including across an animal's visible spectrum. Here we find that larval zebrafish violate this textbook expectation: in the zebrafish brain, UV-stimulation near exclusively gives On-responses, blue/green stimulation mostly Off-responses, and red-light alone elicits approximately balanced On- and Off-responses (see also references2-4). We link these findings to zebrafish visual ecology, and suggest that the observed spectral tuning boosts the encoding of object 'colourfulness', which correlates with object proximity in their underwater world5.

Cathleen Lake and Scott Hawley discuss the components, assembly and functional importance of the synaptonemal complex.

Predation by domestic cats Felis catus can be a threat to biodiversity conservation,1-3 but its mitigation is controversial.4 Confinement and collar-mounted devices can impede cat hunting success and reduce numbers of animals killed,5 but some owners do not wish to inhibit what they see as natural behavior, perceive safety risks associated with collars, or are concerned about device loss and ineffectiveness.6,7 In a controlled and replicated trial, we tested novel, non-invasive interventions that aim to make positive contributions to cat husbandry, alongside existing devices that impede hunting. Households where a high meat protein, grain-free food was provided, and households where 5-10 min of daily object play was introduced, recorded decreases of 36% and 25%, respectively, in numbers of animals captured and brought home by cats, relative to controls and the pre-treatment period. Introduction of puzzle feeders increased numbers by 33%. Fitting Birdsbesafe collar covers reduced the numbers of birds captured and brought home by 42% but had no discernible effect on mammals. Cat bells had no discernible effect. Reductions in predation can be made by non-invasive, positive contributions to cat nutrition and behavior that reduce their tendency to hunt, rather than impede their hunting. These measures are likely to find support among cat owners who are concerned about the welfare implications of other interventions.

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Comment on Curr Biol. 2021 Mar 22;31(6):1317-1325.e8.

Comment on Curr Biol. 2021 Mar 22;31(6):1344-1350.e3.

Many animals use visual cues to navigate their environment. To encode the large input ranges of natural signals optimally, their sensory systems have adapted to the stimulus statistics experienced in their natural habitats1. A striking example, shared across animal phyla, is the retinal tuning to the relative abundance of blue light from the sky, and green light from the ground, evident in the frequency of each photoreceptor type in the two retinal hemispheres2. By adhering only to specific regions of the visual field that contain the relevant information, as for the high-acuity dorsal regions in the eyes of male flies chasing females3, the neural investment can be further reduced. Regionalisation can even lead to activation of the appropriate visual pathway by target location, rather than by stimulus features. This has been shown in fruit flies, which increase their landing attempts when an expanding disc is presented in their frontal visual field, while lateral presentation increases obstacle avoidance responses4. We here report a similar switch in behavioural responses for extended visual scenes. Using a free-flight paradigm, we show that the hummingbird hawkmoth (Macroglossum stellatarum) responds with flight-control adjustments to translational optic-flow cues exclusively in their ventral and lateral visual fields, while identical stimuli presented dorsally elicit a novel directional flight response. This response split is predicted by our quantitative imaging data from natural visual scenes in a variety of habitats, which demonstrate higher magnitudes of translational optic flow in the ventral hemisphere, and the opposite distribution for contrast edges containing directional information.

In the last ten years, the next generation sequencing revolution has multiplied the amount of genetic data for many organisms by orders of magnitude. This has not only led to evolutionary biologists having more data available but also to new and different types of data: from a handful of allozyme markers in the 70s, we got dozens of restriction fragment length polymorphisms (RFLPs) in the 80s, hundreds of microsatellites in the 90s, thousands to hundreds of thousands of single nucleotide polymorphisms (SNPs) in the 2000s, a few full genomes in the 2010s, and thousands of full genomes in the 2020s. These data have provided information not only on the genetic diversity and evolution of the organisms studied but also on genome-wide patterns of selection, linkage disequilibrium, as well as recombination and mutation processes. Below, we will describe how these new genomic data can be used to infer the past demographic history of populations.

Memory forms when a previously neutral stimulus (CS+) becomes competent to predict a biologically potent stimulus (US). However, if the CS+ is repeatedly presented without the US after the memory formation, this memory will be suppressed by newly formed extinction memory.1,2 The striking feature of extinction learning is that it requires repeated trials to robustly form extinction. Extended repetition only yields memories that remain transient in nature,3 thus imposing challenges in understanding the underlying mechanisms of extinction learning. Here, we took advantage of the versatile genetic tools4 and the well-characterized circadian system of Drosophila5,6 to link these unique features to clock neurons. We report that inhibiting the activity of clock neurons blocks the formation of extinction memory. Further investigation attributes this role to a subset of cryptochrome-positive dorsal neurons 1 (DN1s) and their downstream SIFamide neurons. The requirement of clock neurons from a gating mechanism of extinction for a single extinction learning trial robustly causes typical extinction when coupled with acute activation of DN1s, as marked by the initially enhanced but eventually diminished memory suppression. Accordingly, we detected specific neural responses to extinction training in a few DN1s via calcium imaging fulfilled by the TRIC tool,7 but not in dorsal neurons 2 or dorsolateral neurons. Based on these findings, we propose that in extinction of appetitive long-term memory, multiple trials of extinction learning robustly activate DN1 clock neurons to open the gate of extinction, which may contribute to the transient nature of extinction memory.

During the day, flying animals exploit the environmental energy landscape by seeking out thermal or orographic uplift, or extracting energy from wind gradients.1-6 However, most of these energy sources are not thought to be available at night because of the lower thermal potential in the nocturnal atmosphere, as well as the difficulty of locating features that generate uplift. Despite this, several bat species have been observed hundreds to thousands of meters above the ground.7-9 Individuals make repeated, energetically costly high-altitude ascents,10-13 and others fly at some of the fastest speeds observed for powered vertebrate flight.14 We hypothesized that bats use orographic uplift to reach high altitudes,9,15-17 and that both this uplift and bat high-altitude ascents would be highly predictable.18 By superimposing detailed three-dimensional GPS tracking of European free-tailed bats (Tadarida teniotis) on high-resolution regional wind data, we show that bats do indeed use the energy of orographic uplift to climb to over 1,600 m, and also that they reach maximum sustained self-powered airspeeds of 135 km h-1. We show that wind and topography can predict areas of the landscape able to support high-altitude ascents, and that bats use these locations to reach high altitudes while reducing airspeeds. Bats then integrate wind conditions to guide high-altitude ascents, deftly exploiting vertical wind energy in the nocturnal landscape.

Extrusion is a mechanism used to eliminate unfit, excess, or dying cells from epithelial tissues. The initial events guiding which cells will be selectively extruded from the epithelium are not well understood. Here, we induced damage in a subset of epithelial cells in the developing zebrafish and used time-lapse imaging to examine cell and cytoskeletal dynamics leading to extrusion. We show that cell extrusion is preceded by actomyosin contractions that are pulsatile. Our data show that pulsatile contractions are induced by a junctional to medial re-localization of myosin. Analysis of cell area during contractions revealed that cells pulsing with the longest duration and highest amplitude undergo progressive area loss and extrude. Although pulses were driven by local increases in tension, damage to many cells promoted an overall decrease in the tensile state of the epithelium. We demonstrate that caspase activation leads to sphingosine-1-phosphate enrichment that controls both tissue tension and pulses to dictate areas of extrusion. These data suggest that the kinetics of pulsatile contractions define a key behavioral difference between extruding and non-extruding cells and are predictive of extrusion. Altogether, our study provides mechanistic insight into how localized changes in physical forces are coordinated to remove defective cells for homeostatic maintenance of living epithelial tissues.

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Paul Hagerman and Randi Hagerman introduce the X-linked neurodevelopmental disorder Fragile X syndrome (FXS) and discuss what causes this disorder and how it can be treated.

Comment in Curr Biol. 2021 Mar 22;31(6):R303-R306.

Comment in Curr Biol. 2021 Mar 22;31(6):R301-R303.

In plants, the cortical endoplasmic reticulum (ER) network is connected to the plasma membrane (PM) through the ER-PM contact sites (EPCSs), whose structures are maintained by EPCS resident proteins and the cytoskeleton.1-7 Strong co-alignment between EPCSs and the cytoskeleton is observed in plants,1,8 but little is known of how the cytoskeleton is maintained and regulated at the EPCS. Here, we have used a yeast-two-hybrid screen and subsequent in vivo interaction studies in plants by fluorescence resonance energy transfer (FRET)-fluorescence lifetime imaging microscopy (FLIM) analysis to identify two microtubule binding proteins, KLCR1 (kinesin-light-chain-related protein 1) and IQD2 (IQ67-domain 2), that interact with the actin binding protein NET3C and form a component of plant EPCS that mediates the link between the actin and microtubule networks. The NET3C-KLCR1-IQD2 module, acting as an actin-microtubule bridging complex, has a direct influence on ER morphology and EPCS structure. Their loss-of-function mutants, net3a/NET3C RNAi, klcr1, or iqd2, exhibit defects in pavement cell morphology, which we suggest is linked to the disorganization of both actin filaments and microtubules. In conclusion, our results reveal a novel cytoskeletal-associated complex, which is essential for the maintenance and organization of cytoskeletal structure and ER morphology at the EPCS and for normal plant cell morphogenesis.

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Effectively managing farming to meet food demand is vital for the future of biodiversity.1,2 Increasing yields on existing farmland can allow the abandonment (sparing) of low-yielding areas that subsequently recover as secondary forest.2-5 A key question is whether such "secondary sparing" conserves biodiversity more effectively than retaining wildlife-friendly habitat within farmland ("land sharing"). Focusing on the Colombian Choco-Andes, a global hotspot of threatened biodiversity,6 and on cattle farming, we examined the outcomes of secondary sparing and land sharing via simulated scenarios that maintained constant landscape-wide production and equal within-pasture yield: (1) for species and functional diversity of dung beetles and birds; (2) for avian phylogenetic diversity; and (3) across different stages of secondary forest regeneration, relative to spared primary forests. Sparing older secondary forests (15-30 years recovery) promotes substantial species, functional, and phylogenetic (birds only) diversity benefits for birds and dung beetles compared to land sharing. Species of conservation concern had higher occupancy estimates under land-sparing compared to land-sharing scenarios. Spared secondary forests accumulated equivalent diversity to primary forests for dung beetles within 15 years and within 15-30 years for birds, highlighting the need for longer term protection to maximize the biodiversity gains of secondary sparing. Promoting the recovery and protection of large expanses of secondary forests under the land-sparing model provides a critical mechanism for protecting tropical biodiversity, with important implications for concurrently assisting in the delivery of global targets to restore 350 million hectares of forested landscapes.7,8.

Comment in Curr Biol. 2021 Mar 22;31(6):R282-R284. Curr Biol. 2022 Jan 10;32(1):R28-R30. Curr Biol. 2022 Jan 10;32(1):R30-R31.

The mushroom body (MB) of Drosophila melanogaster has multiple functions in controlling memory and behavior.1-9 However, circuit mechanisms that generate this functional diversity are largely unclear. Here, we systematically probed the behavioral contribution of each type of MB output neuron (MBON) by blocking during acquisition, retention, or retrieval of reward or punishment memories. We evaluated the contribution using two conditioned responses: memory-guided odor choice and odor source attraction. Quantitative analysis revealed that these conditioned odor responses are controlled by different sets of MBONs. We found that the valence of memory, rather than the transition of memory steps, has a larger impact on the patterns of required MBONs. Moreover, we found that the glutamatergic MBONs forming recurrent circuits commonly contribute to appetitive memory acquisition, suggesting a pivotal role of this circuit motif for reward processing. Our results provide principles how the MB output circuit processes associative memories of different valence and controls distinct memory-guided behaviors.

Comment in Curr Biol. 2021 Mar 22;31(6):R298-R300.

Comment in Curr Biol. 2021 Mar 22;31(6):R284-R287.

One function of perceptual systems is to construct and maintain a reliable representation of the environment. A useful strategy intrinsic to modern "Bayesian" theories of perception1-6 is to take advantage of the relative stability of the input and use perceptual history (priors) to predict current perception. This strategy is efficient1-7 but can lead to stimuli being biased toward perceptual history, clearly revealed in a phenomenon known as serial dependence.8-14 However, it is still unclear whether serial dependence biases sensory encoding or only perceptual decisions.15,16 We leveraged on the "surround tilt illusion"-where tilted flanking stimuli strongly bias perceived orientation-to measure its influence on the pattern of serial dependence, which is typically maximal for similar orientations of past and present stimuli.7,10 Maximal serial dependence for a neutral stimulus preceded by an illusory one occurred when the perceived, not the physical, orientations of the two stimuli matched, suggesting that the priors biasing current perception incorporate the effect of the illusion. However, maximal serial dependence of illusory stimuli induced by neutral stimuli occurred when their physical (not perceived) orientations were matched, suggesting that priors interact with incoming sensory signals before they are biased by flanking stimuli. The evidence suggests that priors are high-level constructs incorporating contextual information, which interact directly with early sensory signals, not with highly processed perceptual representations.

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Interview with Lesley Weaver, who uses the Drosophila ovary as a model to study how inter-organ communication downstream of nuclear receptor signaling influences oogenesis at Indiana University.

Comment in Curr Biol. 2021 Mar 22;31(6):R306-R309.

Stereocilia on auditory sensory cells are actin-based protrusions that mechanotransduce sound into an electrical signal. These stereocilia are arranged into a bundle with three rows of increasing length to form a staircase-like morphology that is required for hearing. Stereocilia in the shorter rows, but not the tallest row, are mechanotransducing because they have force-sensitive channels localized at their tips. The onset of mechanotransduction during mouse postnatal development refines stereocilia length and width. However, it is unclear how actin is differentially regulated between stereocilia in the tallest row of the bundle and the shorter, mechanotransducing rows. Here, we show actin turnover is increased at the tips of mechanotransducing stereocilia during bundle maturation. Correspondingly, from birth to postnatal day 6, these stereocilia had increasing amounts of available actin barbed ends, where monomers can be added or lost readily, as compared with the non-mechanotransducing stereocilia in the tallest row. The increase in available barbed ends depended on both mechanotransduction and MYO15 or EPS8, which are required for the normal specification and elongation of the tallest row of stereocilia. We also found that loss of the F-actin-severing proteins ADF and cofilin-1 decreased barbed end availability at stereocilia tips. These proteins enriched at mechanotransducing stereocilia tips, and their localization was perturbed by the loss of mechanotransduction, MYO15, or EPS8. Finally, stereocilia lengths and widths were dysregulated in Adf and Cfl1 mutants. Together, these data show that actin is remodeled, likely by a severing mechanism, in response to mechanotransduction.

Comment on Curr Biol. 2021 Mar 22;31(6):1154-1164.e3.

Comment on Curr Biol. 2021 Mar 22;31(6):1261-1267.e3.

Comment on Curr Biol. 2021 Mar 22;31(6):1303-1310.e4.

Comment in Curr Biol. 2021 Mar 22;31(6):R287-R289.

Epithelia must eliminate apoptotic cells to preserve tissue barriers and prevent inflammation.1 Several different mechanisms exist for apoptotic clearance, including efferocytosis2,3 and apical extrusion.4,5 We found that extrusion was the first-line response to apoptosis in cultured monolayers and in zebrafish epidermis. During extrusion, the apoptotic cell elicited active lamellipodial protrusions and assembly of a contractile extrusion ring in its neighbors. Depleting E-cadherin compromised both the contractile ring and extrusion, implying that a cadherin-dependent pathway allows apoptotic cells to engage their neighbors for extrusion. We identify RhoA as the cadherin-dependent signal in the neighbor cells and show that it is activated in response to contractile tension from the apoptotic cell. This mechanical stimulus is conveyed by a myosin-VI-dependent mechanotransduction pathway that is necessary both for extrusion and to preserve the epithelial barrier when apoptosis was stimulated. Earlier studies suggested that release of sphingosine-1-phosphate (S1P) from apoptotic cells might define where RhoA was activated. However, we found that, although S1P is necessary for extrusion, its contribution does not require a localized source of S1P in the epithelium. We therefore propose a unified view of how RhoA is stimulated to engage neighbor cells for apoptotic extrusion. Here, tension-sensitive mechanotransduction is the proximate mechanism that activates RhoA specifically in the immediate neighbors of apoptotic cells, but this also must be primed by S1P in the tissue environment. Together, these elements provide a coincidence detection system that confers robustness on the extrusion response.

Cells from across the eukaryotic tree use actin polymer networks for a wide variety of functions, including endocytosis, cytokinesis, and cell migration. Despite this functional conservation, the actin cytoskeleton has undergone significant diversification, highlighted by the differences in the actin networks of mammalian cells and yeast. Chytrid fungi diverged before the emergence of the Dikarya (multicellular fungi and yeast) and therefore provide a unique opportunity to study actin cytoskeletal evolution. Chytrids have two life stages: zoospore cells that can swim with a flagellum and sessile sporangial cells that, like multicellular fungi, are encased in a chitinous cell wall. Here, we show that zoospores of the amphibian-killing chytrid Batrachochytrium dendrobatidis (Bd) build dynamic actin structures resembling those of animal cells, including an actin cortex, pseudopods, and filopodia-like spikes. In contrast, Bd sporangia assemble perinuclear actin shells and actin patches similar to those of yeast. The use of specific small-molecule inhibitors indicate that nearly all of Bd's actin structures are dynamic and use distinct nucleators: although pseudopods and actin patches are Arp2/3 dependent, the actin cortex appears formin dependent and actin spikes require both nucleators. Our analysis of multiple chytrid genomes reveals actin regulators and myosin motors found in animals, but not dikaryotic fungi, as well as fungal-specific components. The presence of animal- and yeast-like actin cytoskeletal components in the genome combined with the intermediate actin phenotypes in Bd suggests that the simplicity of the yeast cytoskeleton may be due to evolutionary loss.

Locomotion creates various patterns of optic flow on the retina, which provide the observer with information about their movement relative to the environment. However, it is unclear how these optic flow patterns are encoded by the cortex. Here, we use two-photon calcium imaging in awake mice to systematically map monocular and binocular responses to horizontal motion in four areas of the visual cortex. We find that neurons selective to translational or rotational optic flow are abundant in higher visual areas, whereas neurons suppressed by binocular motion are more common in the primary visual cortex. Disruption of retinal direction selectivity in Frmd7 mutant mice reduces the number of translation-selective neurons in the primary visual cortex and translation- and rotation-selective neurons as well as binocular direction-selective neurons in the rostrolateral and anterior visual cortex, blurring the functional distinction between primary and higher visual areas. Thus, optic flow representations in specific areas of the visual cortex rely on binocular integration of motion information from the retina.

Comment in Curr Biol. 2021 Mar 22;31(6):R293-R296.