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Sernagor, E.

Publications and source records attributed to Sernagor, E..

11 recordsLinked to original sources
bioRxiv2026

Developmental Synchrony of Retinal Waves, Apoptosis, and Angiogenesis in Postnatal Retina

Postnatal mouse retinal development is a multi-faceted process involving the coordinated interaction of spontaneous neural activity as retinal waves, vascular plexus growth, and programmed cell death. While these processes are known to interact at a coarse scale, the specific mechanisms integrating them have remained elusive. Using large-scale, widefield calcium imaging, high-density multielectrode array recordings, single cell RNA-seq, and immunohistochemistry, we characterise a tightly aligned centrifugal expansion pattern during retinal development. This pattern is common to stage II retinal wave onsets, vascular development, Heme oxygenase-1 (Hmox1) expressing microglia, apoptotic cell markers, and a novel set of auto-fluorescent cluster complexes (ACCs) identified in this study. Apoptotic cells are known to upregulate functional Pannexin1 (PANX-1) hemichannels. These voltage-gated channels release purinergic molecules which act as "eat me" signals to neighbouring microglia. PANX-1 hemichannel blockade with the drug probenecid results in a profound decrease in spontaneous wave frequency and strength, suggesting that retinal waves are indeed triggered by these apoptotic cells. Taken together, our observations suggest that spontaneous waves are initially triggered in hotspots by hyperactive apoptotic RGCs in unvascularised retinal areas. These apoptotic cells release purinergic molecules via PANX-1 hemichannels, leading to wave generation. This hyperactivity leads to local hypoxic conditions, which, coupled with high extracellular ATP concentrations, promotes angiogenesis. Once blood vessels reach a particular hotspot, ATP release activates Hmox1 positive microglia, which engulf the dying RGCs, creating the auto-fluorescent clusters. Herein, we present a unified mechanism linking causally linking early neural activity, programmed cell death and angiogenesis in the mammalian retina.

neuroscience↗
bioRxiv2025

Photostimulation Improves Maturation of Human Photoreceptors

The human retina contains photoreceptor cells that detect light and enable vision. The development of these cells involves a tightly regulated cascade of structural and molecular events, and their dysfunction leads to irreversible blindness in many retinal diseases. Human retinal organoids derived from stem cells have become powerful tools to model retinal development and disease, but they often remain immature and lack key features required for full function. Light is not only the sensory target of photoreceptors but also an important developmental signal in vivo. However, light has rarely been used as a deliberate stimulus during in vitro differentiation. Here we show that exposing retinal organoids to rhythmic light flicker at a specific frequency enhances photoreceptor maturation across multiple levels. This stimulation improves the development of outer segments, accelerates the transcriptional transition from precursor to mature photoreceptors, and strengthens functional connectivity with downstream neurons. These findings identify patterned light as a potent and physiologically relevant signal for driving retinal development in vitro. This approach represents a non-invasive and easily scalable method for improving the quality of retinal organoids, with implications for disease modelling, drug discovery and the preparation of photoreceptors for cell-based therapies.

cell biology↗
bioRxiv2022

Novel transient cell clusters provide a possible link between early neural activity and angiogenesis in the neonatal mouse retina

Developing neurons become spontaneously active while growing blood vessels begin to irrigate their surroundings. However, surprising little is known about early interactions between neural activity and angiogenesis. In the neonatal mouse retina, spontaneous waves of impulses sweep across the ganglion cell layer (GCL), just underneath the growing superficial vascular plexus. We discovered clusters of transient auto-fluorescent cells in the GCL, forming an annulus that co-localizes with the frontline of the growing plexus. Blood vessel density is highest within cluster areas, suggesting their involvement in angiogenesis. Once the clusters and blood vessels reach the retinal periphery by the end of the first postnatal week, the clusters disappear, eliminated by microglial phagocytosis. Electrical imaging suggests that they have their own electrophysiological signature. Blocking Pannexin1 (PANX1) hemi-channels with probenecid blocks the waves and the fluorescent clusters disappear following prolonged exposure to the drug. Spontaneous waves initiation points follow a developmental center-to-periphery progression similar to the cluster cells. We suggest that these transient cells are specialized, hyperactive neurons residing in the GCL. They generate spontaneous activity hotspots, thereby triggering waves through purinergic paracrine signaling via PANX1 hemi-channels. The strong activity generated around these hotspots triggers angiogenesis, attracting new blood vessels that provide local oxygen supply. Signaling through PANX-1 attracts microglia that establish contact with these cells, eventually leading to their elimination by phagocytosis. These cluster cells may provide the first evidence that specialized transient neuronal populations guide angiogenesis in the developing CNS through neural activity.

neuroscience↗
bioRxiv2021

Retinal self-organization: a model of RGC and SAC mosaic formation

Individual retinal cell types exhibit semi-regular spatial patterns called retinal mosaics. These mosaics enable uniform sampling of visual information and are formed to varying degrees across cell types. Retinal ganglion cells (RGC) and amacrine cells (including starburst amacrine cells (SAC)) are notably known to exhibit such layouts. Mechanisms responsible for the formation of such organised structures and their requirements are still not well understood. Mosaic formation follows three main principles: (1) homotypic cells prevent nearby cells from adopting the same type, (2) cell tangential migration, with homotypic cell repulsion, (3) cell death (with RGCs exhibiting high rates of apoptosis). Here, we use BioDynaMo, an agent-based simulation framework, to build a detailed and mechanistic model of mosaic formation. In particular, we investigate the implications of the three theories for RGCs mosaic formation. We report that the cell migration mechanism yields the most regular mosaics and that cell death can create regular mosaics only if the death rate is kept below 30%, after which cell death has a negative impact on mosaic regularity. In addition, and in accordance with recent studies, we propose here that low density RGC type mosaics exhibit on average low regularities, and thus we question the relevance of regular spacing as a criterion for a group of RGCs to form a RGC type. We also investigate SAC mosaics formation and possible interactions between the ganglion cell layer (GCL) and inner nuclear layer (INL) populations. Investigations are conducted both experimentally and by applying our simulation model to the SAC population. We report that homotypic interactions between the GCL and INL populations during mosaics creation are required to reproduce the observed SAC mosaics characteristics. This suggests that the GCL and INL populations of SACs might not be independent during retinal development. Author SummaryRetinal function depends on cells self-organisation during early development. Understanding the mechanisms underlying this self-organisation could improve not only our comprehension of the retina and its development but also of the cortex. Ultimately, this could lead to novel therapeutic approaches for developmental diseases. Computational models can be of precious help to study this process of self-organisation, given that they are biologically plausible. In this sense, it is important that implemented developmental mechanisms follow the principle of locally available information, without any global knowledge or external supervisor. Here, we follow this principle to investigate mosaic formation during retinal development. In this work, we demonstrate that tangential migration is the only mechanism able to form regular mosaics and that the GCL/INL SAC populations might not be independent during their mosaic formation. More, we question the relevance of regular spacing for RGC types classification.

bioinformatics↗
bioRxiv2021

A novel approach to the functional classification of retinal ganglion cells

Retinal neurons are remarkedly diverse based on structure, function and genetic identity. Classifying these cells is a challenging task, requiring multimodal methodology. Here, we introduce a novel approach for retinal ganglion cell (RGC) classification, based on pharmacogenetics combined with immunohistochemistry and large-scale retinal electrophysiology. Our novel strategy allows grouping of cells sharing gene expression and understanding how these cell classes respond to basic and complex visual scenes. Our approach consists of several consecutive steps. First, the spike firing frequency is increased in RGCs co-expressing a certain gene (Scnn1a or Grik4) using excitatory DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) in order to single out activity originating specifically from these cells. Their spike location is then combined with post hoc immunostaining, to unequivocally characterize their anatomical and functional features. We grouped these isolated RGCs into multiple clusters based on spike train similarities. Using this novel approach. we were able to extend the pre-existing list of Grik4 expressing RGC types to a total of 8 and, for the first time, we provide a phenotypical description of 13 Scnn1a-expressing RGCs. The insights and methods gained here can guide not only RGC classification but neuronal classification challenges in other brain regions as well.

neuroscience↗
bioRxiv2020

Transplanted pluripotent stem cell-derived photoreceptor precursors elicit conventional and unusual light responses in mice with advanced retinal degeneration

Retinal dystrophies often lead to blindness. Developing therapeutic interventions to restore vision is therefore of paramount importance. Here we demonstrate the ability of pluripotent stem cell-derived cone precursors to engraft and restore light responses in the Pde6brd1 mouse, an end-stage photoreceptor degeneration model. Up to 1.5% of precursors integrated into the host retina, differentiated into cones and formed synapses with bipolar cells. Half of the transplanted mice exhibited visual behaviour and 33% showed binocular light sensitivity. The majority of ganglion cells exhibited contrast-sensitive ON, OFF or ON-OFF light responses and even motion sensitivity. Many cells also exhibited unusual responses (e.g. light-induced suppression), presumably reflecting remodelling of the neural retina. Our data indicate that despite relatively low engraftment yield, engrafted pluripotent stem cell-derived cone precursors can elicit light responsiveness even at advanced degeneration stages. Further work is needed to improve engraftment yield and counteract retinal remodelling to achieve useful clinical applications.

neuroscience↗
bioRxiv2020

Nav1.7 gating in human iPSC derived sensory neurons: an experimental and computational study

Chronic pain is a global healthcare problem with a huge societal impact. Its management remains unsatisfactory, with no single treatment clinically approved in most cases. In this study we use an in vitro experimental model of erythromelalgia consisting of sensory neurons derived from human induced pluripotent stem cells obtained from a patient (carrying the mutation F1449V) and a control subject. We combine neurophysiology and computational modelling to focus on the Nav1.7 voltage gated sodium channel, which acts as an amplifier of the receptor potential in nociceptive neurons and plays a critical role in erythromelalgia due to gain of function mutations causing the channel to open with smaller depolarisations. Using multi-electrode array (extracellular) recordings, we found that the scorpion toxin OD1 increases the excitability of sensory neurons in cultures obtained from the control donor, evidenced by increased spontaneous spike rate and amplitude. In erythromelalgia cultures, the application of the Nav1.7 blocker PF-05089771 effectively stopped spontaneous firing. These results, which are in accordance with current clamp and voltage clamp recordings reported in the literature, are explained with a conductance-based computational model of a single human nociceptive neuron. The disease was simulated through a decrease of the Nav1.7 half activation voltage, which decreased the rheobase and increased the response to supra threshold depolarizing currents. This enhanced response could be successfully supressed by blocking the Nav1.7 channels. The painful effects of OD1 were simulated through a slower establishment and a quicker removal of Nav1.7 inactivation, reproducing the effects of the toxin on the spike frequency and amplitude. Our model simulations suggest that the increase in extracellular spike amplitude observed in the MEA after OD1 treatment can be due mainly to a slope increase in the ascending phase of the intracellular spike caused by impaired inactivation gating.

neuroscience↗
bioRxiv2019

Evidence for novel transient clusters of cholinergic ganglion cells in the neonatal mouse retina

Waves of spontaneous activity sweep across the neonatal mouse retinal ganglion cell (RGC) layer, driven by directly interconnected cholinergic starburst amacrine cells from postnatal day (P) 0-10, followed by waves driven by glutamatergic bipolar cells. We found transient clusters of auto-fluorescent cells in the RGC layer during the period of cholinergic waves. They appear around the optic nerve head at P2 and become gradually displaced towards the periphery between P2-8 and then they disappear. Pan-retinal multielectrode array recordings reveal that cholinergic wave origins follow a similar, non-random developmental center-to-periphery pattern. Electrical imaging unmasks hotspots of dipole electrical activity occurring in the vicinity of wave origins. We propose that these activity hotspots are the sites for wave initiation and may originate from the transient cell clusters, reminiscent of activity in transient subplate neurons in the developing cortex, suggesting a universal hyper-excitability mechanism in developing CNS networks during the critical period for brain wiring.

neuroscience↗
bioRxiv2018

Non-parametric physiological classification of retinal ganglion cells

Retinal ganglion cells, the sole output neurons of the retina, exhibit surprising diversity. A recent study reported over 30 distinct types in the mouse retina, indicating that the processing of visual information is highly parallelised in the brain. The advent of high density multi-electrode arrays now enables recording from many hundreds to thousands of neurons from a single retina. Here we describe a method for the automatic classification of large-scale retinal recordings using a simple stimulus paradigm and a spike train distance measure as a clustering metric. We evaluate our approach using synthetic spike trains, and demonstrate that major known cell types are identified in high-density recording sessions from the mouse retina with around 1000 retinal ganglion cells. A comparison across different retinas reveals substantial variability between preparations, suggesting pooling data across retinas should be approached with caution. As a parameter-free method, our approach is broadly applicable for cellular physiological classification in all sensory modalities.

neuroscience↗
bioRxiv2017

Human iPSC-derived RPE and retinal organoids reveal impaired alternative splicing of genes involved in pre-mRNA splicing in PRPF31 autosomal dominant retinitis pigmentosa

Mutations in pre-mRNA processing factors (PRPFs) cause 40% of autosomal dominant retinitis pigmentosa (RP), but it is unclear why mutations in ubiquitously expressed PRPFs cause retinal disease. To understand the molecular basis of this phenotype, we have generated RP type 11 (PRPF31-mutated) patient-specific retinal organoids and retinal pigment epithelium (RPE) from induced pluripotent stem cells (iPSC). Impaired alternative splicing of genes encoding pre-mRNA splicing proteins occurred in patient-specific retinal cells and Prpf31+/- mouse retinae, but not fibroblasts and iPSCs, providing mechanistic insights into retinal-specific phenotypes of PRPFs. RPE was the most affected, characterised by loss of apical-basal polarity, reduced trans-epithelial resistance, phagocytic capacity, microvilli, and cilia length and incidence. Disrupted cilia morphology was observed in patient-derived-photoreceptors that displayed progressive features associated with degeneration and cell stress. In situ gene-editing of a pathogenic mutation rescued key structural and functional phenotypes in RPE and photoreceptors, providing proof-of-concept for future therapeutic strategies.\n\neTOCPRPF31 is a ubiquitously expressed pre-mRNA processing factor that when mutated causes autosomal dominant RP. Using a patient-specific iPSC approach, Buskin and Zhu et al. show that retinal-specific defects result from altered splicing of genes involved in the splicing process itself, leading to impaired splicing, loss of RPE polarity and diminished phagocytic ability as well as reduced cilia incidence and length in both photoreceptors and RPE.\n\nHighlightsO_LISuccessful generation of iPSC-derived RPE and photoreceptors from four RP type 11 patients\nC_LIO_LIRPE cells express the mutant PRPF31 protein and show the lowest expression of wildtype protein\nC_LIO_LIPRPF31 mutations result in altered splicing of genes involved in pre-mRNA splicing in RPE and retinal organoids\nC_LIO_LIPrpf31 haploinsufficiency results in altered splicing of genes involved in pre-mRNA splicing in mouse retina\nC_LIO_LIRPE cells display loss of polarity, reduced barrier function and phagocytosis\nC_LIO_LIPhotoreceptors display shorter and fewer cilia and degenerative features\nC_LIO_LIRPE cells display most abnormalities suggesting they might be the primary site of pathogenesis\nC_LIO_LIIn situ gene editing corrects the mutation and rescues key phenotypes\nC_LI

genetics↗