ANGIOTENSIN-CONVERTING ENZYME IN MURINE TESTIS - STEP-SPECIFIC EXPRESSION OF THE GERMINAL ISOFORM DURING SPERMIOGENESIS

Angiotensin I-converting enzyme (ACE) is known primarily as an endothe lial enzyme that plays a critical role in the regulation of blood pres sure. Another, shorter isoform of ACE is abundantly expressed in the t estes of sexually mature animals. Using antibodies for immunoperoxidas e detection and S-35-labeled riboprobes for in situ hybridization (I SH), we studied the temporal expression and cell distribution of this germinal isoform of ACE in the testis of normal mice and rats as well as of pubertal and sterile mice. In both murine species, specific test icular ACE mRNA and its gene product are present only after completion of meiosis. Through studying two murine species in which spermatogene sis and spermiogenesis have been accurately described, as well as imma ture and sterile animals, it could be shown that ACE mRNA and its corr esponding protein are first synthesized during the cap phase (steps 4- 7). The maximum expression occurred during the acrosome phase (steps 8 -12). ACE mRNA is no longer detectable in spermatids beyond step 14, w hereas its gene product is expressed until the end of spermatid matura tion. Therefore, ACE is exclusively produced in haploid germ cells and belongs to the growing family of proteins whose expression during def inite maturation steps of spermiogenesis appears to be correlated with the unique process of germ cell differentiation.