BETA-HEXOSAMINIDASE IMMUNOLOCALIZATION AND ALPHA-SUBUNIT AND BETA-SUBUNIT GENE-EXPRESSION IN THE RAT TESTIS AND EPIDIDYMIS

beta-hexosaminidase is an essential lysosomal enzyme whose absence in man results in a group of disorders, the G(M2) gangliosidoses. beta-he xosaminidase activity is many times higher in the epididymis than in o ther tissues, is present in sperm, and is postulated to be required fo r mammalian fertilization. To better understand which cells are respon sible for beta-hexosaminidase expression and how it is regulated in th e male reproductive system, we quantitated the mRNA expression of the alpha- and beta-subunits of beta-hexosaminidase and carried out immuno cytochemical localization studies of the enzyme in the vat testis and epididymis, beta-hexosaminidase alpha-subunit mRNA was abundant and di fferentially expressed in the adult rat testis and epididymis, at 13- and 2-fold brain levels, respectively. In contrast, beta-subunit mRNA levels in the testis and epididymis were 0.3- and 5-fold brain levels. During testis development from 7-91 postnatal days of age, testis lev els of alpha-subunit mRNA increased 10-fold and coincided with the app earance of spermatocytes and spermatids in the epithelium; in contrast , beta-subunit mRNA was expressed at low levels throughout testis deve lopment. In isolated male germ cells, beta-hexosaminidase alpha-subuni t expression was most abundant in haploid round spermatids, whereas th e beta-subunit mRNA was not detected in germ cells. Within the epididy mis both alpha- and beta-subunit mRNA concentrations were highest in t he corpus, with 1.5-fold and 9-fold initial segment values, respective ly. Light microscopic immunocytochemistry revealed that beta-hexosamin idase was localized to Sertoli cells and interstitial macrophages in t he testis. In the epididymis, beta-hexosaminidase staining was most in tense in narrow cells in the initial segment, principal cells in the c aput and proximal corpus, and clear cells throughout the duct. Electro n microscopic immunocytochemistry revealed that beta-hexosaminidase wa s predominantly present in lysosomes in Sertoli and epididymal cells. The cellular and regional specificity of beta-hexosaminidase immunoloc alization suggest an important role for the enzyme in testicular and e pididymal functions. (C) 1997 Wiley-Liss, Inc.