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P.F. Hitchcock, M. Ochocinska; NeuroD Expression Is Linked to Rod Neurogenesis in the Retinas of Adult Teleosts . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1649.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In the retinas of teleost fish the bHLH transcription factor NeuroD is expressed by members of the lineage of cells that give rise to rod photoreceptors. The purpose of the study reported here was to quantitatively characterize the relationship between proliferation of rod precursors, the immediate antecedents of rod photoreceptors, and the expression of NeuroD. Methods: Rod precursors were labeled with bromodeoxyuridine (BrdU) by housing goldfish (n=8) for 24hrs in a 5mM solution of BrdU. Standard in situ hybridization techniques using probes derived from zebrafish NeuroD cDNA were used, followed by BrdU immunocytochemistry. Prior to labeling with BrdU, selected animals received an intraperitoneal injection of recombinant trout growth hormone, which stimulates proliferation of all neural progenitors in the retina, including rod precursors. The number of NeuroD-expressing cells, the number of BrdU-labeled cells and the number of double-labeled cells within the outer nuclear layer were counted in 20 sections from the central region of one retina from each animal. Results: The average number of BrdU-labeled cells per section varied from 2.5 to 80.1. The cell counts showed there was a linear relationship between the number of rod precursors labeled with BrdU and: 1) the number of cells expressing NeuroD and 2) the number of double-labeled cells. After the 24hr exposure to BrdU, approximately 40% of the BrdU-labeled rod precursors were expressing NeuroD. Conclusions: The expression of NeuroD is correlated with mitotic activity of rod precursors and thereby the rate of rod genesis. This suggests that for a given rod precursor NeuroD expression is transient and yoked to the cell’s mitotic cycle, although the details of this are not yet known. We infer that NeuroD expression plays a role in determining the fate of rod precursors and in the normal retina reflects the restriction of these cells to the rod photoreceptor fate.
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