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 endothelial enzyme that plays a critical role in the regulation of blood pressure. Another, shorter isoform of ACE is abundantly expressed in the testes of sexually mature animals. Using antibodies for immunoperoxidase detection and [35S]-labeled riboprobes for in situ hybridization (ISH), 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 testicular ACE mRNA and its gene product are present only after completion of meiosis. Through studying two murine species in which spermatogenesis and spermiogenesis have been accurately described, as well as immature and sterile animals, it could be shown that ACE mRNA and its corresponding 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, whereas its gene product is expressed until the end of spermatid maturation. Therefore, ACE is exclusively produced in haploid germ cells and belongs to the growing family of proteins whose expression during definite maturation steps of spermiogenesis appears to be correlated with the unique process of germ cell differentiation.