Abstract
The ability of the testis to convert irreversibly androgens into estrogens is related to the presence of a microsomal enzymatic complex named aromatase, which is composed of a specific glycoprotein, the cytochrome P450 aromatase (P450arom) and an ubiquitous reductase. The aromatase gene is unique in humans and contained 18 exons, 9 of them being translated. In the rat testis we have immunolocalized the P450arom not only in Leydig cells but also in germ cells and especially in elongated spermatids. Related to the stage of germ cell maturation, we have shown that the level of P450arom mRNA transcripts decreases, it is much more abundant in pachytene spermatocytes and round spermatids than in mature germ cells whereas the aromatase activity is 2–4 fold greater in spermatozoa when compared to the younger germ cells. Using a highly specific quantitative competitive RT-PCR method we have evidenced that several factors direct the expression of the aromatase gene in Leydig cells, Sertoli cells, pachytene spermatocytes and round spermatids, and it is obvious that promoter PII is the main one but other promoters could be concerned.In the bank-vole testis we have observed a positive correlation between a fully developed spermatogenesis and a strong immunoreactivity for both P450arom and estrogen receptor β not only in Sertoli cells but also in pachytene spermatocytes and round spermatids. Our recent data obtained from ejaculated human spermatozoa demonstrate the presence of aromatase both in terms of mRNA and protein, and in addition, we suggest that aromatase could be involved in the acquisition of sperm motility. Indeed in men the congenital aromatase deficiency is associated with severe bone maturation problems and sterility. Together with the widespread distribution of estrogen receptors in testicular cells these data clearly show that estrogens play a physiological role in the regulation of spermatogenesis in mammals.
Highlights
The mammalian testis is a complex organ characterised by two main functions : synthesis of steroid hormones and production of spermatozoa
When sperm RNA was used as template in RTPCR we have shown the presence of P450arom transcripts; the sequences alignment from these PCR products and granulosa cells with published human P450arom gene were identical
Using Western blots and a specific monoclonal antibody against aromatase [19] we have evidenced the presence of aromatase in these sperm cells which was obviously more abundant in spermatozoa containing cytoplasmic droplets. These observations are in fitting with other recent data [20], and in addition we have demonstrated that the amount of P450arom transcripts was 30% lower in immotile than in motile spermatozoa [21]
Summary
The mammalian testis is a complex organ characterised by two main functions : synthesis of steroid hormones and production of spermatozoa. In the bank-vole testis we have observed a positive correlation between a fully developed spermatogenesis and a strong immunoreactivity for both P450arom and estrogen receptor β in Sertoli cells and in pachytene spermatocytes and round spermatids.
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