Specific expression of the mRNA for 25 kDA heat-shock protein in the spermatocytes of mouse seminiferous tubules

The 25 kDa heat-shock protein (Hsp25) is a member of the family of small he at-shock proteins. We investigated the expression and cellular localization of Hsp25 mRNA in the testis of adult and developing mice using Northern bl otting and in situ hybridization techniques. In the early postnatal days, i .e., before the onset of spermatogenesis, no Hsp25 mRNA was detected in the testis. At around 10 days postpartum, Hsp25 mRNA began to be expressed in the testis in coincidence with the onset of the first wave of spermatogenes is and increased in amount progressively toward adulthood. Throughout the t estis development, the signal for Hsp25 mRNA was localized exclusively to g erm cells and was not detected in Sertoli or interstitial cells. The testis of W/W nu mutant mice, which lack the germ cell line, exhibited no Hsp25 m RNA expression. In the testis of normal adult mice, the abundance of Hsp25 mRNA differed among the seminiferous tubules in different stages of spermat ogenesis. The most intense signal for Hsp25 mRNA was localized to the sperm atocytes at leptotene, zygotene and early pachytene phases, which are prese nt in the tubules of stages I-III and IX-XII. The signal decreased in inten sity in the late pachytene and diplotene spermatocytes and was not detected in spermatids. Spermatogonia were also devoid of the signal. These results suggested that Hsp25 plays some specific role in the meiotic prophase of t he testicular germ cell.