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J.J. Stanke, A.J. Fischer; Developmental of Cholinergic Amacrine Cells in the Chicken Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):559.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Many studies have characterized the morphological differentiation of cholinergic amacrine cells in the vertebrate retina, but little is known about the genes and factors that regulate the development of these cells. The purpose of this study was to better characterize the genes expressed by type–I and type–II cholinergic amacrine cells and whether the microenvironment providedby the intact embryonic retina influences their differentiation. Methods: We identified cholinergic amacrine cells in the embryonic chick retina by using antibodies to choline acetyltransferase (ChAT) and co–labeled with antibodies to Islet1, Pax6, p27kip1, neurofilament (NF), or cellular retinoic acid binding protein (CRABP). To assay whether the microenvironment influences the relative abundance of type–I and type–II amacrine cells we dissociated E7 retinas, plated them at low density, maintained the cells for four days in culture media then fixed and labeled the cells with antibodies to ChAT and CRABP. Results: We found that as ChAT–immunoreactive cells first formed they expressed the homeodomain transcription factors Pax6 and Islet–1, and the cell–cycle inhibitor p27kip1. As differentiation progressed, type–II cholinergic cells, displaced to the ganglion cell layer, transiently expressed (CRABP), while type–I cells in the inner nuclear layer did not. In addition, type–I and type–II cholinergic cells transiently expressed NF as their terminal arbors were developing within the inner plexiform layer. Levels of neurofilament–immunoreactivity were greater in the neurites of type–II cells in comparison to type–I cells. In dissociated cell cultures, there was twice as many type–I (ChAT positive and CRABP negative) cells relative to the number of type–II cells (ChAT and CRABP positive). Conclusions: We conclude that during development type–I and type–II cholinergic amacrine cells are not homotypic. In addition, we find that developing cholinergic cells in the chick retina are unique among amacrine cells in that they express Islet–1 and neurofilament as they differentiate. We propose that the microenvironment provided within the embryonic retina regulates phenotypic differences between orthotopic and displaced cholinergic amacrine cells.
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