Members of the Usher Gene Family in Zebrafish and Humans Have Conserved Structures and Expression Patterns

Abstract

Abstract: : Purpose: Usher syndrome is the most prevalent cause of syndromic retinitis pigmentosa. We are identifying zebrafish orthologues of the human genes linked to Usher Syndrome to develop a system for investigating expression dynamics, regulation, and potential interactions of the encoded proteins. Methods: Using BLAST comparison with sequences of human USH gene transcripts we identified putative zebrafish orthologues. Fragments of these sequences were amplified from adult zebrafish eye RNA by RT–PCR, subcloned and used as templates for generating antisense RNA probes. To assay gene expression patterns, we performed in situ hybridization with these ush riboprobes on whole and cryosectioned larvae. Results: The zebrafish orthologue of USH1 (myo7a) has been previously reported. We identified orthologues of the remaining 7 known human USH genes. In all cases, functional domains appear highly conserved between the zebrafish and human genes. Thus far, we have examined gene expression patterns for the zebrafish orthologues of USH2A (Usherin) and USH1C (Harmonin). ush2a transcript is present in the developing eye by 48 hours post fertilization (hpf) and can be detected in the neural retina in all larval stages examined. Expression is also observed in the brain, ear, and pineal gland. ush1c transcripts are present in the eye by 72hpf, and in the neural retina, brain and ear of all larval stages examined. Conclusions: The expression patterns of ush2a and ush1c in zebrafish are consistent with the published data from human and mouse. Given their conserved molecular structures, our results suggest that USH expression patterns and gene functions may be evolutionarily conserved. Thus, the zebrafish can serve as a useful model system for examining the roles of these genes in the development and maintenance of retinal cells and will provide further insights into the mechanisms underlying retinal degeneration in Usher Syndrome.

Keywords: retinal degenerations: hereditary • genetics • retinal degenerations: cell biology