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DL Stenkamp, RA Frey; Is ath5 Expression Regulated by Hedgehog (Hh) Signaling During Zebrafish Retinal Development . Invest. Ophthalmol. Vis. Sci. 2002;43(13):826.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We wished to determine whether Hh signals from the midline, and/or from retinal structures, are important for the expression of ath5 during retinal neurogenesis. In embryonic zebrafish, Hh signaling arises from several sources (CNS midline, ganglion cells, and RPE) as the retina develops. Hh proteins can be considered candidates for a midline signal of unknown identity that is indirectly involved in regulating expression of retinal ath5, the vertebrate ortholog of the Drosophila gene, atonal. The ath5 gene product, a basic helix-loop-helix transcription factor, is in turn necessary for ganglion cell neurogenesis. Since Hh signaling from newly-specified ganglion cells is required to propagate retinal neurogenesis, and since hh regulates atonal in the developing Drosophila eye, a similar regulatory relationship has been speculated for the differentiating vertebrate retina. Method: Hh signaling was reduced by the use of sonic-you (syu) mutant zebrafish, which have a deletion in the sonic hedgehog (shh) gene, or by injecting antisense morpholino-conjugated oligonucleotides to knock down expression of both shh and tiggy-winkle hedgehog (twhh) at different developmental times. Expression of ath5 was examined by whole mount in situ hybridization. Results: In the syu mutants, the spatiotemporal pattern of ath5 expression appeared similar to that of wildtype siblings. Following injection of antisense morpholinos at 27 hpf (to disrupt Hh signaling in ganglion cells), some wildtype embryos showed reduced ath5 expression as compared to nonsense morpholino-injected controls. In embryos injected with antisense morpholinos at 10 hpf (to interfere with midline expression of Hh), ath5 expression was more severely affected. Conclusion: Hh signaling may be important for ath5 expression, but both Shh and Twhh must be knocked down. Hh signaling from ganglion cells during retinal neurogenesis, as well as from midline structures earlier in development, may both be important for regulating ath5 expression.
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