IMMUNOCYTOCHEMICAL LOCALIZATION OF GLUTATHIONE-S-TRANSFERASE YO SUBUNIT IN THE RAT TESTIS AND EPIDIDYMIS

The glutathione S-transferases (GSTs) are a family of isozymes that ca talyze the conjugation of glutathione with electrophiles. These protei ns exist as homo- or heterodimers and are separated into five classes (alpha, mu, pi, theta, and sigma). In the present study, the distribut ion of the GST Yo subunit, a member of the mu family, was examined imm unocytochemically in the adult rat testis and epididymis using both li ght microscopy (LM) and electron microscopy (EM). In the testis, an in tense immunoperoxidase reaction was observed over Leydig cells but not macrophages. Within the seminiferous epithelium, only weak reactivity was noted over Sertoli cells, spermatogonia, spermatocytes, and step 1-15 spermatids. There was, however, a progressive and dramatic increa se in the intensity of staining in the cytoplasmic lobes of spermatids between steps 16 and 19. Residual bodies, representing the detached c ytoplasmic robes of the late step 19 spermatids, were also intensely s tained. Initially seen near the lumen of the tubule, they eventually a ppeared at different levels of the tubule at stages IX-XI; none were p resent at stage XII. Cytoplasmic droplets of step 19 spermatids were a lso intensely reactive. After spermiation, the cytoplasmic droplets of spermatozoa. within the proximal region of the epididymis remained in tensely stained. A noticeable decrease in staining was observed in the cauda epididymidis in those droplets that were still there. Quantitat ion of the labeling density (number of gold particles representing ant i-Yo antigenic sites/mu m(2)) paralleled the LM results; for example, between step 15 and 19 spermatids, a greater than sevenfold increase i n labeling density was noted. In the epididymis, a progressive increas e in immunoreactivity was observed over epithelial principal cells fro m the initial segment to the cauda region of this tissue. There was li ttle reactivity over basal, halo, or clear cells. In all reactive cell s, gold particles were distributed randomly throughout the cytoplasmic matrix and nucleus. The present work thus demonstrates that, at the e nd of spermiogenesis, the GST Yo subunit is expressed at high levels i n late spermatids. Furthermore, the presence of this protein in late s permatids and cytoplasmic droplets of spermatozoa suggests that this c onjugating enzyme may play a role in protecting these cells from elect rophilic attack. Also interesting is the correlation between the loss of reactivity in cytoplasmic droplets of spermatozoa of the distal reg ion of the epididymis and the concomitant increase of reactivity in pr incipal cells of this region.