The goal of this study was to identify critical regions of a novel gene, Nance-Horan syndrome-like 1b (nhsl1b). It was previously discovered that C-terminal truncation of the Nhsl1b protein in nhsl1b mutants resulted in a loss of migration in the facial motor neurons of the hindbrain (Walsh et al. 2011). As nhsl1b expresses many isoforms, multiple targets were investigated in order to determine which transcript bears the largest impact on the motor neurons. Using confocal microscopy to observe immunostained embryos, we examined a mutation in an nhsl1b transcript that encodes a WHD, a domain that is known to function within the actin nucleation and polymerization pathways. In situ hybridization and injection of antisense morpholino oligonucleotides indicate that it is not the WHD but another transcript (ex1bnhsl1b) that is necessary for migration. The control experiments for rescuing the mutant phenotype have successfully been performed, but inducing expression of full length nhsl1b in the nhsl1b mutants is proving difficult.

The Nance-Horan syndrome gene (NHS) plays a role in lens, eye and brain development. To date, the function of NHS remains unclear. Recent evidence showed that p53 isoform, Δ113p53, inhibits abnormal cell growth during organogenesis. We show that NHS is expressed in the retinas of Danio rerio and Xenopus tropicalis during key stages of retinogenesis, and that knockdown of the gene resulted in a small eye phenotype in both species. Initially, knockdown of nhsb in zebrafish had no visible defects at 24hpf. But examination of the retina at 48hpf, we see a marked difference in size compared to control embryos. Cell proliferation is a major feature of the developing retina from 24 hpf to 48 hpf. Differentiation of neurons was delayed, while the total number of cells that makes up the volume of the retina was markedly reduced. Here we show that the small retina in nhsb knockdown embryos are due to p53-dependent cell cycle arrest with specific induction of p53 target gene, Δ113p53 and p21. Δ113p53 protects nhsb- knockdown cells from p53-mediated apoptosis. We hypothesize that nhsb overcomes a proliferation restriction in retina progenitor cells during retinogenesis, while knockdown of nhsb increases expression of Δ113p53 and p21, lengthening the cell cycle.