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p57kip2, a KIP family cyclin-dependent kinase (Cdk) inhibitor, blocks the cell cycle by acting on multiple cyclin-Cdk complexes. To investigate the role of p57kip2 in human fertility, the expression of p57kip2 was investigated in testes from normal and obstructive azoospermic male patients who were positive for p57kip2 mRNA. In the seminiferous tubule, strong immunoreactivity of p57kip2 was found in nuclei of early spermatocytes, but not in the spermatogonia. The p57kip2 immunoreactivity in spermatocytes was markedly heterogeneous. Preleptotene spermatocytes showed strong p57kip2 immunoreactivity, but no visible signal was found in late pachytene spermatocytes. Nuclei of the elongating spermatids was also positive for p57kip2 immunoreactivity. Taken together, this suggests that p57kip2 may play a role in the regulation of meiotic progression of early spermatocytes and cell cycle arrest and differentiation of spermatids. p57kip2 immunoreactivity was found in the perinuclear region of the peritubular cells, but not in the Sertoli cells. In Leydig cells, moderate immunoreactivity of p57kip2 was largely found in the cytoplasm, suggesting the noble function of p57kip2 in the differentiation of adult Leydig cells.

The effects of progesterone on the acrosome reaction, as well as the effects of RU486 on the progesterone-induced acrosome reaction in capacitated boar spermatozoa, were investigated. Progesterone, a major steroid that is secreted by the cumulus cells of oocyte, clearly induced the acrosome reaction in a dose-dependent manner in capacitated boar spermatozoa, even though it failed to show similar effects in non-capacitated spermatozoa. RU486, a potent antiprogestin, significantly reduced the effects of progesterone on the progesterone-induced acrosome reaction; however, when treated alone, it showed no inhibitory effects on the acrosome reaction. The inhibitory effects of RU486 were also shown to be dose dependent. These results imply that in addition to the wellknown inducer of the acrosome reaction, zona pellucida, progesterone can also induce the acrosome reaction through its specific receptors on spermatozoa after the spermatozoa undergo capacitation.

The purified 32 kDa boar sperm protease, known as the 32 kDa sperminogen, was identified by reverse transcription polymerase chain reaction (RT-PCR) and Northern blot analysis following its partial peptide sequencing. The 32 kDa boar sperm protease was purified from the acid extracts of boar spermatozoa and subjected to CNBr-digestion. The most prominently digested 30 kDa product was purified by HPLC and its peptide sequence was analyzed. NCBI Blast search of the analyzed 21 amino acid sequence revealed that the sequence matched 91% with that of proacrosin. DNA primer was deduced from the analyzed peptide sequence and the 32 kDa protease was further identified by RT-PCR. Upon RT-PCR, 1 Kbp DNA fragment was amplified, which is the expected length if the product was amplified from the proacrosin mRNA, implying that there is no separate mRNA for the 32 kDa sperminogen. To confirm these results, Northern blot analysis was performed. Four DNA probes generated from the exons of proacrosin genomic DNA sequence all detected a single species of mRNA, suggesting that there is no separate mRNA for the 32 kDa sperminogen which might be produced either from the potential separate 32 kDa sperminogen gene or by differential splicing from proacrosin mRNA. These results strongly suggest that the 32 kDa protease is part of the proacrosin/acrosin system, and that the 32 kDa sperminogen might be formed from post-translational processing of proacrosin.