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A. C. Morris, J. M. Fadool; Transcription Factor C-myb: A Candidate Regulator of Rod Photoreceptor Genesis and Regeneration in Zebrafish. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1275.
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In contrast to adult mammals, the retinas of fish exhibit persistent neurogenesis and the capacity for injury-induced regeneration. In the mature zebrafish retina, a subset of Müller glia generate neural progenitors that constitute the apex of the rod photoreceptor lineage. Little is known about the control of neural progenitor production by Müller glia or how this lineage is reprogrammed to generate cones or other retinal neurons following injury. To identify genes important for adult photoreceptor genesis and regeneration, we compared the expression profile of wild type retinas with those from zebrafish that experience rod degeneration. c-myb was one of several genes displaying increased expression in response to rod degeneration. We evaluated the expression pattern of c-myb in the developing and mature zebrafish retina, in wild-type animals and in mutants that exhibit selective loss of rods or cones.
c-myb expression was examined by RT-PCR, whole-mount in situ hybridization and by analysis of a cmyb-GFP transgenic zebrafish line. Localization of c-myb expression in different retinal cell types was determined by in situ hybridization on adult retinal cryosections and by immunolabeling with antibodies to cell-type specific markers. Gene expression was analyzed in wild type zebrafish, in XOPS-mCFP animals, which experience rod degeneration, and in the pde6cw59 cone degeneration mutant.
In zebrafish embryos, c-myb expression was detectable at 24 hours post fertilization (hpf) throughout the retinal neuroepithelium and persisted in the developing retina through 72 hpf. By 5 days post fertilization (dpf), c-myb expression was restricted to a subset of Müller glia. At 15 dpf, c-myb expression was observed in a subset of rod progenitor cells and in a few Müller cells. Some, but not all, of the cmyb-GFP+ rod progenitor cells were also BrdU+. Often, GFP+ rod progenitors were located in close proximity to a GFP+ Müller cell. Expression of c-myb was not detected in mature photoreceptors, nor was it observed in the proliferative marginal zone. Expression of c-myb was elevated in retinas from both rod and cone degeneration mutants.
A function for c-myb in retinal development and photoreceptor regeneration has not been previously described. Our results suggest that c-myb plays a role both in embryonic retinal development and in the persistent generation of rod photoreceptors in adult zebrafish. Our data also indicate that c-myb is involved in the regenerative response to both rod and cone photoreceptor degeneration, and that it may be a marker for the neurogenic subset of Müller glia.
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