Osteocrin: identification, expression, and CRISPR/Cas9 analysis in scale development in teleost

Abstract

The completion of channel catfish genome sequencing provides a possibility of performing comparative genome studies. The comparative genome study between scaleless channel catfish and armor-scaled (bony dermal plate) catfish, such as common pleco (Pterygoplichthys pardalis) and striped Raphael catfish (Platydoras armatulus) reveal one gene namely osteocrin (ostn) was absent from channel catfish genome but present in armored-scale catfish genome. Additional BLAST analysis indicated that the osteocrin, however, was found in several scaled fishes, but was absent in the scaleless fish genome, suggesting that it could be a potential candidate gene involved in scale development, but detailed analysis of the status of ostn in various fishes has not been conducted. This initial observation is in line with the known functions of osteocrin in the development of calcified tissues such as bone. In this work, we conducted extensive comparative genome analysis to validate the correlation of the presence osteocrin with scaled fishes, and the absence of osteocrin with scaleless fishes. We found scaled fish model in phylogeny tree clustered based on their scale types: placoid, ganoid, cosmoid, elasmoid, and dermal bony plate, respectively. Next, we determined the expression patterns of the osteocrin genes during scale regeneration in common carp. Finally, we conducted a knockout experiment using CRISPR/Cas9 system to determine the phenotypes of osteocrin knockouts in zebrafish as the model. The disruption of ostn resulted in a number of phenotype defects, including pigment dispersion, imperfect operculum and asymmetrical gill rakers, bone deformities, slow scale growth, and partial scale lost on the heterozygous mutant zebrafish. Keywords: osteocrin, genome comparative, scale regeneration, CRISPR/Cas9