Michel Joseph Roux

Background: Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder that primarily affects the cerebellum and retina. SCA7 is caused by a polyglutamine expansion in the ATXN7 protein, a subunit of the transcriptional coactivator SAGA that acetylates histone H3 to deposit narrow H3K9ac mark at DNA regulatory elements of active genes. Defective histone acetylation has been presented as a possible cause for gene deregulation in SCA7 mouse models. However, the topography of acetylation defects at the whole genome level and its relationship to changes in gene expression remain to be determined.Methods: We performed deep RNA-sequencing and chromatin immunoprecipitation coupled to high-throughput sequencing to examine the genome-wide correlation between gene deregulation and alteration of the active transcription marks,e.g.SAGA-related H3K9ac, CBP-related H3K27ac and RNA polymerase II (RNAPII), in a SCA7 mouse retinopathy model.Results: Our analyses revealed that active transcription marks are reduced at most gene promoters in SCA7 retina, while a limited number of genes show changes in expression. We found that SCA7 retinopathy is caused by preferential downregulation of hundreds of highly expressed genes that define morphological and physiological identities of mature photoreceptors. We further uncovered that these photoreceptor genes harbor unusually broad H3K9ac profiles spanning the entire gene bodies and have a low RNAPII pausing. This broad H3K9ac signature co-occurs with other features that delineate superenhancers, including broad H3K27ac, binding sites for photoreceptor specific transcription factors and expression of enhancer-related non-coding RNAs (eRNAs). In SCA7 retina, downregulated photoreceptor genes show decreased H3K9 and H3K27 acetylation and eRNA expression as well as increased RNAPII pausing, suggesting that superenhancer-related features are altered.Conclusions: Our study thus provides evidence that distinctive epigenetic configurations underlying high expression of cell-type specific genes are preferentially impaired in SCA7, resulting in a defect in the maintenance of identity features of mature photoreceptors. Our results also suggest that continuous SAGA-driven acetylation plays a role in preserving post-mitotic neuronal identity.

At the first retinal synapse, horizontal cells (HCs) contact both photoreceptor terminals and bipolar cell dendrites, modulating information transfer between these two cell types to enhance spatial contrast and mediate color opponency. The synaptic mechanisms through which these modulations occur are still debated. The initial hypothesis of a GABAergic feedback from HCs to cones has been challenged by pharmacological inconsistencies. Surround antagonism has been demonstrated to occur via a modulation of cone calcium channels through ephaptic signaling and pH changes in the synaptic cleft. GABAergic transmission between HCs and cones has been reported in some lower vertebrates, like the turtle and tiger salamander. In these reports, it was revealed that GABA is released from HCs through reverse transport and target GABA receptors are located at the cone terminals. In mammalian retinas, there is growing evidence that HCs can release GABA through conventional vesicular transmission, acting both on autaptic GABA receptors and on receptors expressed at the dendritic tips of the bipolar cells. The presence of GABA receptors on mammalian cone terminals remains equivocal. Here, we looked specifically for functional GABA receptors in mouse photoreceptors by recording in the whole-cell or amphotericin/gramicidin-perforated patch clamp configurations. Cones could be differentiated from rods through morphological criteria. Local GABA applications evoked a Cl⁻ current in cones but not in rods. It was blocked by the GABA_A receptor antagonist bicuculline methiodide and unaffected by the GABA_C receptor antagonist TPMPA [(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid]. The voltage dependency of the current amplitude was as expected from a direct action of GABA on cone pedicles but not from an indirect modulation of cone currents following the activation of the GABA receptors of HCs. This supports a direct role of GABA released from HCs in the control of cone activity in the mouse retina.

In the original published version of the article, Valerie Vancollie was mistakenly omitted from the list of members of the International Mouse Phenotyping Consortium. In addition, recognition of funding from Wellcome Trust grant WT098051 was mistakenly omitted from the Acknowledgements.The errors have been corrected in both the PDF and HTML versions of the paper.

Despite advances in next generation sequencing technologies, determining the genetic basis of ocular disease remains a major challenge due to the limited access and prohibitive cost of human forward genetics. Thus, less than 4,000 genes currently have available phenotype information for any organ system. Here we report the ophthalmic findings from the International Mouse Phenotyping Consortium, a large-scale functional genetic screen with the goal of generating and phenotyping a null mutant for every mouse gene. Of 4364 genes evaluated, 347 were identified to influence ocular phenotypes, 75% of which are entirely novel in ocular pathology. This discovery greatly increases the current number of genes known to contribute to ophthalmic disease, and it is likely that many of the genes will subsequently prove to be important in human ocular development and disease.

Panton-Valentine leukocidin (PVL) retinal intoxication induces glial activation and inflammatory response via the interaction with retinal neurons. In this study, rabbit retinal explant was used as a model to study neuronal and glial consequences of PVL intoxication. Retinal explants were treated with different concentrations of PVL. PVL location and neuronal and glial changes were examined using immunohistochemistry. Some inflammatory factors were quantified using RT-qPCR at 4 and 8 h. These results were compared with those of control explants. PVL co-localized rapidly with retinal ganglion cells and with horizontal cells. PVL induced Müller and microglial cell activation. Retinal structure was altered and some amacrine and microglial cells underwent apoptosis. Glial activation and cell apoptosis increased in a PVL concentration- and time-dependent manner. IL-6 and IL-8 expression increased in PVL-treated explants but less than in control explants, which may indicate that other factors were responsible for glial activation and retinal apoptosis. On retinal explants, PVL co-localized with neuronal cells and induced glial activation together with microglial apoptosis, which confirms previous results observed in in vivo model. Rabbit retinal explant seems to be suitable model to further study the process of PVL leading to glial activation and retinal cells apoptosis.

With three models in commercial use, artificial retinas are the most concrete hope to restore sight to blind patients, notably those affected with retinitis pigmentosa. However, present architectures are costly to produce, while the restored visual acuity remains below the legal threshold for blindness. Furthermore, the complexity of current systems with tethered application‐specific integrated circuits (asics) requires complex surgeries, with risks of complications and failures. In the search for new nanomaterials, it is demonstrated that, when placed in contact with photoreceptors (control mouse retinas) or directly with bipolar cells (rhodopsin^P23H mouse retinas, a model of retinitis pigmentosa), films of vertically aligned anatase titanium dioxide (TiO₂) nanotubes can drive the activity of the retinal network for stimulation frequencies up to the video rate (25 Hz), in response to short (5–20 ms), small (50–100 µm) light spots. Acting as continuous arrays of electrodes, these films should allow a fine tuning of prosthetic stimulations, through modulation of the spot size, duration, and precise localization over the implant surface.

Purpose: The purpose of this study was to quantify the frequency and severity of ocular abnormalities affecting wild-type C57BL/6N mice, the most common strain used worldwide for the creation of single-gene knockouts. Methods: A total of 2773 animals (5546 eyes) were examined at one colony at UC Davis and in three more colonies at the Institut Clinique de la Souris in Strasbourg, France. Mice were examined at 15 to 16 weeks postnatal age by performing anterior segment biomicroscopy, posterior segment examination by indirect ophthalmoscopy, intraocular pressure measurement, and optical coherence tomography of anterior and posterior segment structures. Results: Common ocular findings in the C57BL/6N strain included corneal deposits (3%), increased optical density of the anterior lens capsule (67%), punctate nuclear cataracts (98%), vitreous crystalline deposits (61%), hyaloid vascular remnant (6%), and retinal dysplasia attributed to the rd8 mutation (58%). Interestingly, retinal dysplasia was more common in male mice in all four breeding colonies evaluated in this study. The thickness of ocular tissues and compartments were measured by spectral-domain optical coherence tomography, including the central cornea, anterior chamber, vitreous, and retinal layers. Intraocular pressure was measured by rebound tonometry. Conclusions: Ocular abnormalities are common in anterior and posterior segments of the C57BL/6N mouse, the most common background on which single-gene knockout mice have been made. It is important that vision scientists understand the extent and variability of ocular findings associated with this particular genetic background of mice.