Differential expression of photoreceptor-specific genes in the retina of a zebrafish cadherin2 mutant glass onion and zebrafish cadherin4 morphants

Cadherins are Ca(2+) -dependent transmembrane molecules that mediate cell-cell adhesion through homophilic interactions. Cadherin2 (also called N-cadherin) and cadherin4 (also called R-cadherin), members of the classic cadherin subfamily, have been shown to be involved in development of a variety of tissues and organs including the visual system. To gain insight into cadherin2 and cadherin4 function in differentiation of zebrafish photoreceptors, we have analyzed expression patterns of several photoreceptor-specific genes (crx, gnat1, gnat2, irbp, otx5, rod opsin, rx1, and uv opsin) and/or a cone photoreceptor marker (zpr-1) in the retina of a zebrafish cadherin2 mutant, glass onion (glo) and in zebrafish embryos injected with a cadherin4 specific antisense morpholino oligonucleotide (cdh4MO). We find that expression of all these genes, and of zpr-1, is greatly reduced in the retina of both the glo and cadherin4 morphants. Moreover, in these embryos, expression of some genes (e.g. gnat1, gnat2 and irbp) is more affected than others (e.g. rod opsin and uv opsin). In embryos with both cadherins functions blocked (glo embryos injected with the cdh4MO), the eye initially formed, but became severely and progressively disintegrated and expressed little or no crx and otx5 as development proceeded. Our results suggest that cadherin2 and cadherin4 play important roles in the differentiation of zebrafish retinal photoreceptors.