Cathepsin C transcripts are differentially expressed in the final stages of oocyte maturation in kuruma prawn Marsupenaeus japonicus

To elucidate the molecular mechanism of oocyte maturation in the kuruma prawn (Marsupenaeus japonicus), subtractive suppression hybridization (SSH) was initially used to identify novel up-regulated genes during the final stages of oocyte maturation, followed by evaluation of the differential expression profile by macroarray and quantitative real-time RT-PCR analyses. The cathepsin C (dipeptidyl peptidase I) gene was thus found to exhibit a significantly higher expression around the onset of cortical rod (CR) formation (early CR stage, appearance of round CRs), progress to a higher mRNA level until the middle CR stage (elongation of CRs), then rapidly revert to a low expression level at the late CR stage (occurrence of germinal vesicle breakdown, GVBD), as also observed at the non-CR stage (previtellogenesis and vitellogenesis). In situ hybridization analyses revealed that the sites of the expression of cathepsin C transcripts in the ovary were distributed in both oocyte and follicle cells, particularly at the early CR stage. A full-length cDNA sequence of this stage-specific gene was subsequently determined by rapid amplification of the cDNA 3′ and 5′ ends (3′ and 5′ RACE). The deduced amino acid sequence of the 230-residue mature peptide shared 67-70% identity to the known cathepsin C in mammals. Western blot analysis showed that expression of procathepsin C protein was exclusively at CR stages. The storage site of procathepsin C protein was localized in CRs as revealed by immunohistochemical analysis. This is the first report on the full-length cDNA sequence of cathepsin C and a demonstration of its involvement in the final stages of oocyte maturation in crustacean species.