Ptf1a triggers GABAergic neuronal cell fates in the retina

International audienceBACKGROUND: In recent years, considerable knowledge has been gained on the molecular mechanisms underlying retinal cell fate specification. However, hitherto studies focused primarily on the six major retinal cell classes (five types of neurons of one type of glial cell), and paid little attention to the specification of different neuronal subtypes within the same cell class. In particular, the molecular machinery governing the specification of the two most abundant neurotransmitter phenotypes in the retina, GABAergic and glutamatergic, is largely unknown. In the spinal cord and cerebellum, the transcription factor Ptf1a is essential for GABAergic neuron production. In the mouse retina, Ptf1a has been shown to be involved in horizontal and most amacrine neurons differentiation. RESULTS: In this study, we examined the distribution of neurotransmitter subtypes following Ptf1a gain and loss of function in the Xenopus retina. We found cell-autonomous dramatic switches between GABAergic and glutamatergic neuron production, concomitant with profound defects in the genesis of amacrine and horizontal cells, which are mainly GABAergic. Therefore, we investigated whether Ptf1a promotes the fate of these two cell types or acts directly as a GABAergic subtype determination factor. In ectodermal explant assays, Ptf1a was found to be a potent inducer of the GABAergic subtype. Moreover, clonal analysis in the retina revealed that Ptf1a overexpression leads to an increased ratio of GABAergic subtypes among the whole amacrine and horizontal cell population, highlighting its instructive capacity to promote this specific subtype of inhibitory neurons. Finally, we also found that within bipolar cells, which are typically glutamatergic interneurons, Ptf1a is able to trigger a GABAergic fate. CONCLUSION: Altogether, our results reveal for the first time in the retina a major player in the GABAergic versus glutamatergic cell specification genetic pathway

Etude des voies de signalisation paracrines et autocrines qui contrôlent la différenciation chondrogénique et ostéogénique d'une cellule souche mésoblastique

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Stemness or not stemness? Current status and perspectives of adult retinal stem cells.

International audienceMany retinal dystrophies are associated with photoreceptor loss, which causes irreversible blindness. The recent identification of various sources of stem cells in the mammalian retina has raised the possibility that cell-based therapies might be efficient strategies to treat a wide range of incurable eye diseases. A first step towards the successful therapeutic exploitation of these cells is to unravel intrinsic and extrinsic regulators that control their proliferation and cell lineage determination. In this review, we provide an overview of the different types and molecular fingerprints of retinal stem cells identified so far. We also detail the current knowledge on molecular cues that influence their self-renewal and proliferation capacity. In particular, we focus on recent data implicating developmental signaling pathways, such as Wnt, Notch and Hedeghog, both in the normal and regenerating retina in different animal models. Last, we discuss the potential of ES cells and various adult stem cells for retinal repair

Stem Cells and Regeneration in the Xenopus Retina

International audienceThe ability to regenerate damaged cells in the retina varies tremendously among species, being restricted for most of them to specific developmental stages. Regarding vertebrates, only the newt was thought to exhibit full regenerative capacity upon retinectomy in the adulthood. The recent discovery that the anuran amphibian Xenopus can regenerate its retina after metamorphosis opened new avenues to investigate the cellular and molecular mechanisms involved in this process. In this review, we provide an historical overview of regeneration studies in Xenopus. Particular emphasis is given to the cellular sources contributing to retinal replacement, the involvement of tissue interactions and the importance of the injury paradigm. We also describe recent progress and promises in the field brought by the development of 3D tissue culture methods and transgenic Xenopus models

Paracrine and autocrine signals promoting full chondrogenic differentiation of a mesoblastic cell line.

International audienceThe pluripotent mesoblastic C1 cell line was used under serum-free culture conditions to investigate how paracrine and autocrine signals cooperate to drive chondrogenesis. Sequential addition of two systemic hormones, dexamethasone and triiodothyronine, permits full chondrogenic differentiation. The cell intrinsic activation of the BMP signaling pathway and Sox9 expression occurring on mesoblastic condensation is insufficient for recruitment of the progenitors. Dexamethasone-dependent Sox9 upregulation is essential for chondrogenesis.Differentiation of lineage stem cells relies on cell autonomous regulations modulated by external signals. We used the pluripotent mesoblastic C1 cell line under serum-free culture conditions to investigate how paracrine and autocrine signals cooperate to induce differentiation of a precursor clone along the chondrogenic lineage

Hedgehog signaling and the retina: insights into the mechanisms controlling the proliferative properties of neural precursors

Hedgehog signaling has been linked to cell proliferation in a variety of systems; however, its effects on the cell cycle have not been closely studied. In the vertebrate retina, Hedgehog's effects are controversial, with some reports emphasizing increased proliferation and others pointing to a role in cell cycle exit. Here we demonstrate a novel role for Hedgehog signaling in speeding up the cell cycle in the developing retina by reducing the length of G1 and G2 phases. These fast cycling cells tend to exit the cell cycle early. Conversely, retinal progenitors with blocked Hedgehog signaling cycle more slowly, with longer G1 and G2 phases, and remain in the cell cycle longer. Hedgehog may modulate cell cycle kinetics through activation of the key cell cycle activators cyclin D1, cyclin A2, cyclin B1, and cdc25C. These findings support a role for Hedgehog in regulating the conversion from slow cycling stem cells to fast cycling transient amplifying progenitors that are closer to cell cycle exit

CRISPR/Cas9-Mediated Models of Retinitis Pigmentosa Reveal Differential Proliferative Response of Müller Cells between <i>Xenopus laevis</i> and <i>Xenopus tropicalis</i>

Retinitis pigmentosa is an inherited retinal dystrophy that ultimately leads to blindness due to the progressive degeneration of rod photoreceptors and the subsequent non-cell autonomous death of cones. Rhodopsin is the most frequently mutated gene in this disease. We here developed rhodopsin gene editing-based models of retinitis pigmentosa in two Xenopus species, Xenopus laevis and Xenopus tropicalis, by using CRISPR/Cas9 technology. In both of them, loss of rhodopsin function results in massive rod cell degeneration characterized by progressive shortening of outer segments and occasional cell death. This is followed by cone morphology deterioration. Despite these apparently similar degenerative environments, we found that Müller glial cells behave differently in Xenopus laevis and Xenopus tropicalis. While a significant proportion of Müller cells re-enter into the cell cycle in Xenopus laevis, their proliferation remains extremely limited in Xenopus tropicalis. This work thus reveals divergent responses to retinal injury in closely related species. These models should help in the future to deepen our understanding of the mechanisms that have shaped regeneration during evolution, with tremendous differences across vertebrates