Knock-down of the Zebrafish Orthologue of the Retinitis Pigmentosa 2 (RP2) Gene Results in Retinal Degeneration

PURPOSE The present study investigates the expression and function of the zebrafish orthologue of the Retinitis Pigmentosa 2 (RP2) gene. METHODS Zebrafish RP2 (ZFRP2) cDNA was isolated from adult eye mRNA by reverse transcription-polymerase chain reaction (RT-PCR). Gene expression was examined by RT-PCR. The deduced peptide sequence was aligned with RP2 orthologues from different species. Translational suppression (knock-down) of zebrafish RP2 was carried out by antisense morpholino-injection. The phenotype of ZFRP2 knock-down morphants was characterised by immunohistology and histology. Human wildtype and mutant RP2 mRNAs were co-injected with ZFRP2 morpholinos to test whether human RP2 mRNA could rescue ZFRP2 knock-down phenotypes. RESULTS ZFRP2 encodes a protein of 376 amino acids containing an N-terminal tubulin folding cofactor C-like domain and a C-terminal nucleoside diphosphate kinase-like domain. It shares 63-65% amino acid identity with human, mouse and bovine RP2. RP2 is expressed at the earliest stages of zebrafish development and persists into adulthood. Knock-down of RP2 in zebrafish causes a curved body axis and small eye phenotype, associated with increased cell death throughout the retina. Human wildtype RP2 mRNA could rescue the body curvature phenotype of ZFRP2 morphants, and the eye size of the resultant morphants was significantly increased over that of morphants in which ZFRP2 had been depleted. CONCLUSIONS Zebrafish RP2 is widely expressed throughout development. ZFRP2 knockdown caused retinal degeneration in zebrafish. Human RP2 could partially rescue the small eye phenotype of ZFRP2 morphants.