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Item The Direct Reprogramming of Somatic Cells: Establishment of a Novel System for Photoreceptor Derivation(2013-08-22) Steward, Melissa Mary; Meyer, Jason S.; Dai, Guoli; Randall, Stephen Karl, 1953-; Atkinson, SimonPhotoreceptors are a class of sensory neuronal cells that are deleteriously affected in many disorders and injuries of the visual system. Significant injury or loss of these cells often results in a partial or complete loss of vision. While previous studies have determined many necessary components of the gene regulatory network governing the establishment, development, and maintenance of these cells, the necessary and sufficient profile and timecourse of gene expression and/or silencing has yet to be elucidated. Arduous protocols do exist to derive photoreceptors in vitro utilizing pluripotent stem cells, but only recently have been able to yield cells that are disease- and/or patient-specific. The discovery that mammalian somatic cells can be directly reprogrammed to another terminally-differentiated cell phenotype has inspired an explosion of research demonstrating the successful genetic reprogramming of one cell type to another, a process which is typically both more timely and efficient than those used to derive the same cells from pluripotent stem cell sources. Therefore, the emphasis of this study was to establish a novel system to be used to determine a minimal transcriptional network capable of directly reprogramming mouse embryonic fibroblasts (MEFs) to rod photoreceptors. The tools, assays, and experimental design chosen and established herein were designed and characterized to facilitate this determination, and preliminary data demonstrated the utility of this approach for accomplishing this aim.Item Meckelin 3 is Necessary for Photoreceptor Outer Segment Development(2012-07-03) Hudson, Scott R.; Belecky-Adams, Teri; Gattone II, Vince; Blazer-Yost, Bonnie; Atkinson, SimonCiliopathies with multiorgan pathology include renal cysts and eye pathology. Previous studies showed meckelin (MKS3 protein product) are crucial to cilia function and its absence in Wpk rats (with mutated rMks3 gene) causes Leber's congenital amaurosis. Retinal photoreceptors have connecting cilium that joins the inner to the outer segment and plays a role in the transport of molecules necessary for morphological and molecular development and maintenance of the outer segment process. The present study evaluated meckelin expression during normal postnatal retinal development and the consequences of mutant meckelin on photoreceptor development and survival in Wistar-Wpk/Wpk rat. Meckelin was co-expressed in photoreceptors, amacrine, Muller glia and ganglion cells in postnatal day 10 (P10) and P21 wild type retinae. Meckelin was detected in both inner and outer segments of photoreceptors. By P10, both wild type and homozygous Wpk mutant retina had all retinal cell types. In contrast, by P21, cells expressing photoreceptor-specific markers in the Wpk mutant were fewer in number with abnormal expression patterns. Cell death assays confirmed a significant amount of cells undergoing apoptosis in the outer nuclear layer of the mutant rat retina. By electron microscopy, mutant photoreceptors did not develop an outer segment process beyond a connecting cilium and rudimentary outer segment. We conclude that MKS3 is not important for formation of connecting cilium and rudimentary outer segments, but is critical for the elongation and/or maintenance of mature outer segment processes.Item Retinal Wnt signaling defect in a zebrafish fetal alcohol spectrum disorder model(PLOS, 2018-08-01) Muralidharan, Pooja; Sarmah, Swapnalee; Marrs, James A.; Biology, School of ScienceFetal alcohol spectrum disorder caused by prenatal alcohol exposure includes ocular abnormalities (microphthalmia, photoreceptor dysfunction, cataracts). Zebrafish embryos exposed to ethanol from gastrulation through somitogenesis show severe ocular defects, including microphthalmia and photoreceptor differentiation defects. Ethanol-treated zebrafish had an enlarged ciliary marginal zone (CMZ) relative to the retina size and reduced Müller glial cells (MGCs). Ethanol exposure produced immature photoreceptors with increased proliferation, indicating cell cycle exit failure. Signaling mechanisms in the CMZ were affected by embryonic ethanol exposure, including Wnt signaling in the CMZ, Notch signaling and neurod gene expression. Retinoic acid or folic acid co-supplementation with ethanol rescued Wnt signaling and retinal differentiation. Activating Wnt signaling using GSK3 inhibitor (LSN 2105786; Eli Lilly and Co.) restored retinal cell differentiation pathways. Ethanol exposed embryos were treated with Wnt agonist, which rescued Wnt-active cells in the CMZ, Notch-active cells in the retina, proliferation, and photoreceptor terminal differentiation. Our results illustrate the critical role of Wnt signaling in ethanol-induced retinal defects.