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Manuela Lahne, Samantha Piekos, Kristin M Ackerman, David R Hyde; Photoregulation of rod precursor cell proliferation in the adult zebrafish retina. Invest. Ophthalmol. Vis. Sci. 2016;57(12):554.
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© ARVO (1962-2015); The Authors (2016-present)
Persistent neurogenesis of rod photoreceptors in the adult zebrafish retina is mediated by proliferating Müller glia that produce neuronal progenitor cells (NPCs), which in turn generate rod precursor cells that differentiate into rod photoreceptors. Previously, it was shown that rod precursor cell proliferation is regulated in a circadian manner. Thus, we determined whether prolonged periods of darkness affected rod precursor proliferation.
Albino, albino Tg[gfap:EGFP] or albino Tg[olig2:EGFP] zebrafish that express EGFP in Müller glia or NPCs, respectively, were maintained in the dark for either 0, 2, 5, 8, 11 or 14 days in system water or for 8 days in system water supplemented with or without 0.4 or 0.8 g/l taurine. A subset of fish was intraperitoneally injected with 1 mM EdU on day 0 or BrdU on either day 2, 5, 8, 11 or 14. Eyes were fixed two hours after EdU or BrdU exposure. Some dark-adapted albino Tg[gfap:EGFP] zebrafish were exposed to constant intense light for 0, 16, 25 and 30 hours. Retinal sections were examined for proliferation (proliferating cellular nuclear antigen (PCNA), BrdU, EdU) and cell death (TUNEL).
The number of PCNA-positive cells was significantly increased in the retinal outer nuclear layer (ONL) of zebrafish that were dark-adapted for 14 days compared to those maintained under standard light-conditions. In contrast, the number of gfap:EGFP-negative PCNA-positive ONL cells (rod precursor cells) were not different in retinas from dark-adapted zebrafish that were exposed to constant intense light for 0, 16, 25 or 30 hours. Dark-adaptation-induced rod precursor proliferation that peaked at 8 days did not result from photoreceptor cell death or increased Müller glia or NPC proliferation. An EdU/BrdU labeling experiment revealed that similar numbers of cells underwent S-phase throughout the timecourse, suggesting that rod precursor cell differentiation into rod photoreceptors rather than proliferation might be affected. However, exposure to taurine, which plays a role in rod photoreceptor differentiation in vitro did not reduce the dark-adaptation-induced rod precursor cell proliferation.
Dark-adaptation stimulated rod precursor cell proliferation. This increased proliferation was not due to cell death, upregulated Müller glia/NPC proliferation, nor rod photoreceptor differentiation. Thus, the mechanism remains unknown.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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