Biology subjects

Lucas, R. J.

Publications and source records attributed to Lucas, R. J..

At least 19 recordsLinked to original sources

bioRxiv2026

Parallel visual processing in the suprachiasmatic region of a diurnal mammal.

Light shapes mammalian physiology and behaviour through hypothalamic pathways, yet how these pathways process visual information in day-active species remains poorly understood. Based largely on work in nocturnal rodents, the suprachiasmatic nucleus (SCN) is classically viewed as a retinal target that encodes ambient illumination for circadian entrainment. We combine anatomical tracing, light-evoked c-Fos mapping and high-density silicon-probe electrophysiology to define visual processing in the suprachiasmatic region of the diurnal murid Rhabdomys pumilio. We find that retinal input and light-evoked activity extend beyond the SCN into rostral and lateral peri-SCN hypothalamus. Within the SCN, neurons encode irradiance with graded changes in maintained firing broadly similar to those observed in parallel recordings of nocturnal Mus domesticus. Across the wider suprachiasmatic region, Rhabdomys neurons show selectivity for more dynamic visual stimuli, including luminance transitions, contrast and temporal structure. Unsupervised clustering identifies five functionally distinct hypothalamic visual response classes with different anatomical distributions. These findings reveal an expanded hypothalamic visual network in a diurnal mammal, placing SCN irradiance coding within a broader system for processing dynamic visual features.

neuroscience↗

bioRxiv2026

Photoswitchable optoGPCRs for reversible control of Gs and arrestin signalling

OptoGPCRs are light-activatable G protein-coupled receptors (GPCRs) used for optogenetic control of physiological processes. Most existing optoGPCRs are based on monostable opsins, which are limited by photobleaching and irreversibility. The bistable jumping spider rhodopsin 1 (JSR1) carrying the single point mutant S199F introduces a [~]150 nm spectral separation between the active and inactive states, enabling bidirectional control with distinct wavelengths of light. Here, we show that JSR1-S199F demonstrates robust, light-reversible arrestin recruitment and Gq/i protein activity. We then engineered JSR1-S199F-based optoGPCRs with Gs protein activity, expanding the limited repertoire of bistable Gs-coupled opsins. Specifically, we present optoDRD1, a chimeric optoGPCR that redirects the native Gq/i protein activity of JSR1 towards the Gs pathway of the dopamine D1 receptor (DRD1). Through systematic screening of intracellular domain combinations, we identified an optimal chimeric configuration comprising ICL2, ICL3, helix 8, and the C-terminus from DRD1. The resulting optoGPCR is activated by violet light ({lambda}max = 397 nm) and deactivated by green light ({lambda}max = 531 nm) at physiologically relevant light intensities. A single violet light pulse drives sustained Gs signalling for several hours, while green light deactivation enables precise signal termination at any timepoint. OptoDRD1 closely mimics wild-type DRD1 signalling kinetics and G protein selectivity. Compared to JellyOp, the only previously characterised natively Gs-coupled opsin, optoDRD1 shows higher signal amplitude and reversibility over multiple light cycles. We further demonstrate optoDRD1s utility for optogenetic control of Gs-regulated processes in vitro, including insulin secretion in human {beta}-cells and signalling modulation in a neuronal cell line, supporting its potential for in vivo applications. The biochemical stability and known structure of JSR1 make it a robust scaffold for this rational engineering and for future biophysical characterization. Together, optoDRD1 and JSR1-S199F expand the optoGPCR toolkit and open new opportunities for dissecting dopaminergic signalling, Gs-mediated physiology, and GPCR signalling pharmacology.

synthetic biology↗

bioRxiv2025

Development of visible light-sensitive human OPN5 via single amino acid substitution

Animal opsins, light-sensitive G-protein-coupled receptors (GPCRs), serve as primary light receptors in animals, supporting vision and providing light-dependent regulation of physiology and behaviour. Animal opsins also show great potential to be used as optogenetic tools that regulate cellular G protein signalling with light. Opn5 is a UV-sensitive "non-visual" opsin that is expressed in a wide range of tissues throughout body. Although Opn5 could be a good template for the development of optogenetic tools applicable to tissues outside of the eye because of its broad expression, its sensitivity to poorly tissue-penetrating UV light poses challenges for its application. In this study, we focused on human OPN5 (hOPN5) to attempt to identify amino acid(s) responsible for the UV sensitivity and to shift the spectral sensitivity to visible light. Sequence alignment across UV-sensitive Opn5s identified a conserved lysine reside (Lys91) at a position implicated in spectral tuning in invertebrate opsins. We applied site-directed mutagenesis to replace this residue with neutral (alanine) or acidic (glutamate or aspartate) amino acids. Heterologous action spectroscopy of these mutants revealed substantial shifts in spectral sensitivity (55-63nm) toward visible wavelengths. Our findings identify Lys91 as a key spectral tuning site in hOPN5 and provide visible-light sensitive versions of this protein as a candidate for optogenetic applications.

biophysics↗

bioRxiv2024

Enhanced restoration of visual code after targeting on bipolar cells compared to retinal ganglion cells with optogenetic therapy

Optogenetic therapy is a promising vision restoration method where light sensitive opsins are introduced to the surviving inner retina following photoreceptor degeneration. The cell type targeted for opsin expression will likely influence the quality of restored vision. However, a like-for-like pre-clinical comparison of visual responses evoked following equivalent opsin expression in the two major targets, ON bipolar (ON BCs) or retinal ganglion cells (RGCs), is absent. We address this deficit by comparing stimulus-response characteristics at single unit resolution in retina and dorsal lateral geniculate nucleus (dLGN) of retinally degenerate mice genetically engineered to express the opsin ReaChR in Grm6- or Brn3c-expressing cells (ON BC vs RGCs respectively). For both targeting strategies, we find ReaChR-evoked responses have equivalent sensitivity and can encode contrast across different background irradiances. Compared to ON BCs, targeting RGCs decreased response reproducibility and resulted in more stereotyped responses with reduced diversity in response polarity, contrast sensitivity and temporal frequency tuning. Recording ReaChR-driven responses in visually intact retinas confirmed that RGC-targeted ReaChR expression disrupts visual feature selectivity of individual RGCs. Our data show that while both approaches restore visual responses with impressive fidelity, ON BC targeting produces a richer visual code better approaching that of wildtype mice.

neuroscience↗

bioRxiv2024

Reconfiguration of the visual code and retinal cell type complement in closely related diurnal and nocturnal mice

How does evolution act on neuronal populations to match computational characteristics to functional demands? We address this problem by comparing visual code and retinal cell composition in closely related murid species with different behaviours. Rhabdomys pumilio are diurnal and have substantially thicker inner retina and larger visual thalamus than nocturnal Mus musculus. High-density electrophysiological recordings of visual response features in the dorsal lateral geniculate nucleus (dLGN) reveals that Rhabdomys attains higher spatiotemporal acuity both by denser coverage of the visual scene and a selective expansion of elements of the code characterised by non-linear spatiotemporal summation. Comparative analysis of single cell transcriptomic cell atlases reveals that realignment of the visual code is associated with increased relative abundance of bipolar and ganglion cell types supporting OFF and ON-OFF responses. These findings demonstrate how changes in retinal cell complement can reconfigure the coding of visual information to match changes in visual needs.

neuroscience↗

bioRxiv2023

Beyond Lux: Methods for Species and Photoreceptor-Specific Quantification of Ambient Light for Mammals

BackgroundLight is a key environmental regulator of physiology and behaviour. Mistimed or insufficient light disrupts circadian rhythms and is associated with impaired health and well-being across mammals. Appropriate lighting is therefore crucial for indoor housed mammals. The most commonly used measurement for lighting is lux. However, this employs a spectral weighting function based on human perceived brightness and is not suitable for non-visual effects of light or use across species. In humans, a photoreceptor-specific (-opic) metrology system has been proposed as a more appropriate way of measuring light. ResultsHere we establish technology to allow this -opic measurement approach to be readily extended to any mammalian species, accounting for differences in photoreceptor types, photopigment spectral sensitivities, and eye anatomy. Since measuring photopigment spectral sensitivity can be hard to derive for novel animals and photoreceptors, we developed a high-throughput, easy-to-use, method to derive spectral sensitivities for recombinantly expressed melanopsins and use it to establish the spectral sensitivity of melanopsin from 12 non-human mammals. We further address the need for simple measurement strategies for species-specific -opic measures by developing an accessible online toolbox for calculating these units and validating an open hardware, low-cost, multichannel light sensor for point and click measurement. We finally demonstrate that species-specific -opic measurements are superior to photopic lux as predictors of physiological responses to light in mice and allow ecologically relevant comparisons of photosensitivity between species. ConclusionOur study demonstrates that measuring light more accurately using species-specific -opic units is superior to the existing unit of photopic lux and holds the promise of improvements to the health and welfare of animals, scientific research reproducibility, agricultural productivity, and energy usage.

neuroscience↗

bioRxiv2023

Evolution of neuronal cell classes and types in the vertebrate retina

The basic plan of the retina is conserved across vertebrates, yet species differ profoundly in their visual needs (Baden et al., 2020). One might expect that retinal cell types evolved to accommodate these varied needs, but this has not been systematically studied. Here, we generated and integrated single-cell transcriptomic atlases of the retina from 17 species: humans, two non-human primates, four rodents, three ungulates, opossum, ferret, tree shrew, a teleost fish, a bird, a reptile and a lamprey. Molecular conservation of the six retinal cell classes (photoreceptors, horizontal cells, bipolar cells, amacrine cells, retinal ganglion cells [RGCs] and Muller glia) is striking, with transcriptomic differences across species correlated with evolutionary distance. Major subclasses are also conserved, whereas variation among types within classes or subclasses is more pronounced. However, an integrative analysis revealed that numerous types are shared across species based on conserved gene expression programs that likely trace back to the common ancestor of jawed vertebrates. The degree of variation among types increases from the outer retina (photoreceptors) to the inner retina (RGCs), suggesting that evolution acts preferentially to shape the retinal output. Finally, we identified mammalian orthologs of midget RGCs, which comprise >80% of RGCs in the human retina, subserve high-acuity vision, and were believed to be primate-specific (Berson, 2008); in contrast, the mouse orthologs comprise <2% of mouse RGCs. Projections both primate and mouse orthologous types are overrepresented in the thalamus, which supplies the primary visual cortex. We suggest that midget RGCs are not primate innovations, but descendants of evolutionarily ancient types that decreased in size and increased in number as primates evolved, thereby facilitating high visual acuity and increased cortical processing of visual information.

neuroscience↗

bioRxiv2022

Functional integrity of visual coding following advanced photoreceptor degeneration

Photoreceptor degeneration sufficient to produce severe visual loss often spares the inner retina. This raises the hope that treatments using optogenetics or electrical stimulation, which generate a replacement light input signal in surviving neurons, may restore vision. The success of these approaches is dependent on the capacity of surviving circuits in the early stages of the visual system to generate and propagate an appropriate visual code in the face of neuroanatomical remodelling. To determine the capacity of surviving circuits in advanced retinal degeneration to present an appropriate visual code, we generated a transgenic mouse expressing the optogenetic actuator ReaChR in ON bipolar cells (second order neurons in the visual projection). After crossing this with the rd1 model of photoreceptor degeneration, we compared ReaChR derived responses with photoreceptor-driven responses in wildtype (WT) mice in retinal ganglion cells and visual thalamus. The ReaChR-driven responses in rd1 animals showed low photosensitivity, but in other respects generated a visual code that was very similar to WT. Furthermore, ReaChR rd1 units in the retina had high response reproducibility and showed sensitivity normalisation to code contrast stably across different background intensities. At the single unit level, ReaChR-derived responses exhibited broadly similar variation in light response polarity, contrast sensitivity and temporal frequency tuning as WT. Units from WT and ReaChR rd1 mice clustered together when subjected to unsupervised community detection based on stimulus-response properties. Our data reveal an impressive ability for surviving circuitry to recreate a rich visual code following advanced retinal degeneration and are promising for regenerative medicine in the central nervous system.

neuroscience↗

bioRxiv2022

Look-up and look-down neurons in the mouse visual thalamus during freely moving exploration

The traditional view that visuomotor integration is a property of higher brain centres has recently been challenged by the discovery in head-fixed rodents that locomotion increases neuronal activity throughout the early visual system (including the retina). Any appreciation of the importance of this behavioural modulation of visual inputs must encompass a comprehensive understanding of the range of behaviours engaged by this mechanism. This information is unavailable from head-fixed preparations in which head and body postures are fundamentally constrained and dissociated from their natural coupling with visual experience. We addressed this deficit by recording spiking activity from the primary visual thalamus during freely moving exploration, while simultaneously applying frame-by-frame quantification of postures and movements to robust 3D reconstructions of head and body. We found that postures associated with the animal looking up/down affected activity in >50% neurons. The extent of this effect was comparable to that induced by locomotion. Moreover, the two effects were largely independent and jointly modulated neuronal activity. Thus, while most units were excited by locomotion, some expressed highest firing when the animal was looking up ("look up" neurons) while others when the animal was looking down ("look-down" neurons). These results were observed in the dark, thus representing a genuine behavioural modulation, and were amplified in a lit arena. These findings define the influence of natural exploratory behaviour on activity in the early visual system and reveal the importance of up/down postures in gating neuronal activity in the primary visual thalamus.

neuroscience↗

bioRxiv2021

Two light sensors decode moonlight versus sunlight to adjust a plastic circadian/circalunidian clock to moon phase

Many species synchronize their physiology and behavior to specific hours. It is commonly assumed that sunlight acts as the main entrainment signal for ~24h clocks. However, the moon provides similarly regular time information, and increasingly studies report correlations between diel behavior and lunidian cycles. Yet, mechanistic insight into the possible influences of the moon on ~24hr timers is scarce. We studied Platynereis dumerilii and uncover that the moon, besides its role in monthly timing, also schedules the exact hour of nocturnal swarming onset to the nights darkest times. Moonlight adjusts a plastic clock, exhibiting <24h (moonlit) or >24h (no moon) periodicity. Abundance, light sensitivity, and genetic requirement indicate Platynereis r-Opsin1 as receptor to determine moonrise, while the cryptochrome L-Cry is required to discriminate between moon- and sunlight valence. Comparative experiments in Drosophila suggest that Cryptochromes requirement for light valence interpretation is conserved. Its exact biochemical properties differ, however, between species with dissimilar timing ecology. Our work advances the molecular understanding of lunar impact on fundamental rhythmic processes, including those of marine mass spawners endangered by anthropogenic change.

neuroscience↗

bioRxiv2021

Analyses of cephalic and non-cephalic sensory cell types provide insight into joint photo- and mechanoreceptor evolution

Rhabdomeric Opsins (r-Opsins) are light-sensors in cephalic eye photoreceptors, but also function in additional sensory organs. This has prompted questions on the evolutionary relationship of these cell types, and if ancient r-Opsins cells were non-photosensory. Our profiling of cephalic and non-cephalic r-opsin1-expressing cells of the marine bristleworm Platynereis dumerilii reveals shared and distinct features. Non-cephalic cells possess a full set of phototransduction components, but also a mechanosensory signature. We determine that Pdu-r-Opsin1 is a Gq-coupled blue-light receptor. Profiling of cells from r-opsin1 mutants versus wild-types, and a comparison under different light conditions reveals that in the non-cephalic cells, light - mediated by r-Opsin1 - adjusts the expression level of a calcium transporter relevant for auditory mechanosensation in vertebrates. We establish a deep learning-based quantitative behavioral analysis for animal trunk movements, and identify a light-and r-Opsin-1-dependent fine-tuning of the worms undulatory movements in headless trunks, which are known to require mechanosensory feedback. Our results suggest an evolutionary concept in which r-Opsins act as ancient, light-dependent modulators of mechanosensation, and suggest that light-independent mechanosensory roles of r-Opsins likely evolved secondarily.

developmental biology↗

bioRxiv2020

Daily electrical activity in the master circadian clock of a diurnal mammal

Daily or circadian rhythms in mammals are orchestrated by a master circadian clock within the hypothalamic suprachiasmatic nuclei (SCN). Here, cell-autonomous oscillations in gene expression, intrinsic membrane properties, and synaptic communication shape the electrical landscape of the SCN across the circadian day, rendering SCN neurons overtly more active during the day than at night. This well-accepted hallmark bioelectrical feature of the SCN has overwhelmingly emerged from studies performed on a small number of nocturnal rodent species. Therefore, for the first time, we investigate the spontaneous and evoked electrical activity of SCN neurons in a diurnal mammal. To this end, we measured the electrical activity of individual SCN neurons during the day and at night in brain slices prepared from the diurnal murid rodent Rhabdomys pumilio and then developed cutting-edge data assimilation and mathematical modelling approaches to uncover the underlying ionic mechanisms. We find that R. pumilio SCN neurons were more excited in the day than at night, recapitulating the prototypical pattern of SCN neuronal activity previously observed in nocturnal rodents. By contrast, the evoked activity of R. pumilio neurons included a prominent suppressive response that is not present in the SCN of nocturnal rodents. Our computational modelling approaches reveal transient subthreshold A-type potassium channels as the primary determinant of the suppressive response and highlight a key role for this ionic mechanism in tuning excitability of clock neurons and optimising SCN function to accommodate R. pumilios diurnal niche.

neuroscience↗

bioRxiv2020

Daytime light enhances the amplitude of circadian output in a diurnal mammal

Mammalian circadian rhythms are orchestrated by a master pacemaker in the hypothalamic suprachiasmatic nuclei (SCN), which receives information about the 24 h light:dark cycle from the retina. The accepted function of this light signal is to reset circadian phase in order to ensure appropriate synchronisation with the celestial day. Here, we ask whether light also impacts another key property of the circadian oscillation, its amplitude. To this end, we measured rhythms in behavioural activity and body temperature, and SCN electrophysiological activity in the diurnal murid rodent Rhabdomys pumilio following stable entrainment to 12:12 light:dark cycles at 4 different daytime intensities (ranging from 12.77 to 14.80 log melanopsin effective photons/cm2/s). Rhabdomys showed strongly diurnal activity and body temperature rhythms in all conditions, but measures of rhythm robustness were positively correlated with daytime irradiance under both entrainment and subsequent free run. Whole-cell and extracellular recordings of electrophysiological activity in ex vivo SCN revealed substantial differences in electrophysiological activity between dim and bright light conditions. At lower daytime irradiance, daytime peaks in SCN spontaneous firing rate and membrane depolarisation were substantially depressed, leading to an overall marked reduction in the amplitude of circadian rhythms in spontaneous activity. Our data reveal a previously unappreciated impact of daytime light intensity on SCN physiology and the amplitude of circadian rhythms, and highlight the potential importance of daytime light exposure for circadian health.

neuroscience↗

bioRxiv2020

Using a bistable animal opsin for switchable and scalable optogenetic inhibition of neurons

There is no consensus on the best optogenetic tool for neuronal inhibition. Lamprey parapinopsin ( Lamplight) is a Gi/o-coupled bistable animal opsin that can be activated and deactivated by short and long wavelength light, respectively. Since native mechanisms of neuronal inhibition frequently employ Gi/o signalling, we asked here whether Lamplight could be used for optogenetic silencing. We show that short (405nm) and long (525nm) wavelength pulses repeatedly switch Lamplight between stable signalling active and inactive states, and that combining these wavelengths can be used to achieve intermediate levels of activity. We demonstrate that these properties can be applied to produce switchable and scalable neuronal hyperpolarisation, and suppression of spontaneous spike firing in the mouse hypothalamic suprachiasmatic nucleus. We show that expressing Lamplight in (predominantly) ON bipolar cells can photosensitise retinas following advanced photoreceptor degeneration, and that 405 and 525nm stimuli can produce responses of opposite sign in output neurons of the retina. Lamplight-driven responses to both activating (405nm) and deactivating (525nm) light can occur within 500ms and be elicited by intensities at least 10x below threshold for available inhibitory optogenetic tools. We conclude that Lamplight can co-opt endogenous signalling mechanisms to allow optogenetic inhibition that is scalable, sustained and rapidly reversible.

neuroscience↗

bioRxiv2020

Optogenetic control of the Bone Morphogenetic Protein signalling pathway through engineered blue light-sensitive receptors

Bone Morphogenetic Proteins (BMPs) are members of the Transforming Growth Factor {beta} (TGF{beta}) superfamily and have crucial roles during development; including mesodermal patterning and specification of renal, hepatic and skeletal tissues. In vitro developmental models currently rely upon costly and unreliable recombinant BMP proteins that do not enable dynamic or precise perturbation of the BMP signalling pathway. Here, we develop a novel optogenetic BMP signalling system (optoBMP) that enables rapid induction of the canonical BMP signalling pathway through illumination with blue light. We demonstrate the utility of the optoBMP system in multiple human cell lines to initiate signal transduction through phosphorylation and nuclear translocation of SMAD1/5, leading to upregulation of BMP target genes including Inhibitors of DNA binding ID2 and ID4. Furthermore, we demonstrate how the optoBMP system can be used to fine-tune activation of the BMP signalling pathway through variable light stimulation. Optogenetic control of BMP signalling will enable dynamic and high-throughput intervention across a variety of applications in cellular and developmental systems.

molecular biology↗

bioRxiv2020

Beyond locomotion: in the mouse the mapping between sensations and behaviours unfolds in a higher dimensional space

Instinctive defensive behaviours, consisting of stereotyped sequences of movements and postures, are an essential component of the mouse behavioural repertoire. Since defensive behaviours can be reliably triggered by threatening sensory stimuli, the selection of the most appropriate action depends on the stimulus property. However, since the mouse has a wide repertoire of motor actions, it is not clear which set of movements and postures represent the relevant action. So far this has been empirically identified as a change in locomotion state. However, the extent to which locomotion alone captures the diversity of defensive behaviours and their sensory specificity is unknown. To tackle this problem we developed a method to obtain a faithful 3D reconstruction of the mouse body that enabled to quantify a wide variety of motor actions. This higher dimensional description revealed that defensive behaviours are more stimulus-specific than indicated by locomotion data. Thus, responses to distinct stimuli that were equivalent in terms of locomotion (e.g. freezing induced by looming and sound) could be discriminated along other dimensions. The enhanced stimulus-specificity was explained by a surprising diversity. A clustering analysis revealed that distinct combinations of movements and postures, giving rise to at least 7 different behaviours, were required to account for stimulus-specificity. Moreover, each stimulus evoked more than one behaviour revealing a robust one-to-many mapping between sensations and behaviours that was not apparent from locomotion data. Our results indicate that diversity and sensory specificity of mouse defensive behaviours unfold in a higher dimensional space spanning multiple motor actions.

animal behavior and cognition↗

bioRxiv2020

Infra-slow modulation of fast beta/gamma oscillations in the mouse visual system.

Infra-slow (<0.02 Hz) and fast beta/gamma (20 - 100 Hz) oscillations in neurophysiological activity have been widely found in the subcortical visual system. While it is well established that fast beta/gamma oscillations are involved in visual processing, the role (if any) of infra-slow oscillations is currently unknown. One possibility is that infra-slow oscillations exert influence by modulating the amplitude of fast oscillations, yet the extent to which these different oscillations arise independently and interact remains unknown. We addressed these questions by recording in vivo spontaneous activity from subcortical visual system of visually intact mice, and animals whose retinal network was disrupted by advanced rod/cone degeneration (rd/rd cl) or melanopsin loss (Opn4-/- We found many neurons expressing only one type of oscillation, and indeed fast oscillations were absent in rd/rd cl. Conversely, neurons co-expressing the two oscillations were also common, and were encountered more often than expected by chance in visually intact but not Opn4-/- mice. Finally, where they co-occurred we found that beta/gamma amplitude was modulated by the infra-slow rhythm. Our data thus reveal that: 1.) infra-slow and beta-gamma oscillations are separable phenomena; and 2.) that they actively co-occur in a subset of neurones in which the phase of infra-slow oscillations define beta-gamma oscillation amplitude. These findings suggest that infra-slow oscillations could influence vision by modulating beta-gamma oscillations, and raise the possibility that disruptions in these oscillatory behaviours contribute to vision dysfunction in retinal dystrophy. KEY POINTS SUMMARYO_LINeurophysiological activity in the subcortical visual system fluctuates in both infra-slow and fast oscillatory ranges, however the level of co-occurrence and potential functional interaction of these rhythms is unknown. C_LIO_LIAnalyzing dark-adapted spontaneous activity in the mouse subcortical visual system, we find that these two types of oscillation interact uniquely through a population of neurons expressing both rhythms. C_LIO_LIGenetic ablation of rod/cone signaling potentiates infra-slow and abolishes fast beta/gamma oscillations while genetic ablation of melanopsin substantially diminishes the interaction between these two rhythms. C_LIO_LIOur results indicate that in an intact visual system the phase of infra-slow modulates fast beta/gamma oscillations. C_LIO_LIThus one possible impact of infra-slow oscillations in vision is to guide visual processing by interacting with fast narrowband oscillations. C_LI

neuroscience↗

bioRxiv2019

Extraocular, rod-like photoreceptors in a flatworm express xenopsin photopigment

Animals detect light using opsin photopigments. One recently classified opsin clade, the xenopsins, found in lophotrochozoans, challenges our views on opsin and photoreceptor evolution. Originally thought to belong to the Gi-coupled ciliary opsins, xenopsins are now understood to have diverged from ciliary opsins in pre-bilaterian times, but little is known about the cells that deploy these proteins, or if they form a photopigment and drive phototransduction. We characterized xenopsin in a flatworm, Maritigrella crozieri, and found that it is expressed in a larval eyespot, and in an abundant extraocular cell type around the adult brain. These distinct cells house hundreds of cilia in an intra-cellular vacuole (a phaosome). Cellular assays show Mc xenopsin forms a photopigment and couples to Gi/o in response to light. These findings reveal a novel photoreceptor cell type and opsin/G-protein couple, and highlight the convergent enclosure of photosensitive cilia in flatworm phaosomes and jawed vertebrate rods.

zoology↗