Ubiquitin C-terminal hydrolase as a putative factor involved in sex differentiation of fish (temperate wrasse, Halichoeres poecilopterus).

Temperate wrasse (Halichoeres poecilopterus) is known to undergo sex transition from female to male (protogyny). In order to detect factors related to male sex differentiation which appear during sex transition, we compared protein constituents between transitional and mature gonads by two-dimensional gel electrophoresis. Eight proteins were found to increase in amount considerably in the transitional gonads in comparison with the counterparts in ovaries. Five of the eight proteins were also found in mature testes. One of the proteins shared by testes and transitional gonads had an isoelectric point at pH 5.3 and an apparent molecular weight of 26 kDa. Thus we termed the protein p 26. It was abundant in degenerating ovary, transitional gonad, and mature testis and less abundant in mature ovary and brain. Therefore, the expression of p 26 seemed to start during sex transition and continue during maturation of the testis. Amino acid sequence analysis revealed high homology of p 26 to ubiquitin C-terminal hydrolase, which is supposed to cleave ubiquitin associated with nuclear proteins and a transcriptional repressor. Therefore, p 26 was supposed to regulate gene expression through the mediation of ubiquitin. Proteins which seemed to be counterparts of p 26 were detected in testes of two other fish species by an antiserum against p 26. These results suggest that p 26 is a possible candidate for the factor which is related to sex differentiation.