Characterization and expression pattern of r-spondin1 in Cynoglossus semilaevis.

r-spondin1 (rspo1) encodes a secreted protein that is involved in the determination and differentiation of the mammalian ovary. However, little information is yet available for teleosts. Here, we identified a homologue of rspo1 in Cynoglossus semilaevis. The full-length cDNA of rspo1 had a length of 2,703 bp with an open reading frame of 834 bp, encoding a protein with a length of 277 amino-acids. rspo1 expression was detected via qRT-PCR in various tissues, and significant sexually dimorphic expression was observed in the gonads. Furthermore, ISH located rspo1 in germ cells such as spermatogonia, spermatocytes, spermatids, spermatozoa, and oocytes, as well as in somatic cells of the gonads. Following knockdown of rspo1 in an ovarian cell line, the expressions of wnt4a, β-catenin, foxl2, and StAR were highly affected; wnt4a and β-catenin were significantly downregulated, whereas foxl2 and StAR were significantly upregulated. In summary, these data suggest that rspo1 may be involved in the regulation of ovarian development and differentiation through a conserved pathway, while the function of the gene in the testis remains elusive.