The testicular aromatase: from gene to physiological role.

The aromatase is the terminal enzyme responsible for estrogen biosynthesis. It is present in the endoplasmic reticulum membrane of steroidogenic cells. The aromatase gene is unique and its expression is regulated in a tissue and more precisely, in a cell-specific manner via the alternative use of various promoters located in the first exon I. Physiological role of estrogens in the regulation of mammalian testicular functions is indicated by: 1/the aromatase gene expression and its transduction in a fully active protein in somatic cells as well in germ cells of testes, 2/ the widespread distribution of estrogen receptors (ERalpha and ERbeta) in the genital tract of the male. Our recent data showing that human ejaculated spermatozoa expressed specific transcripts for P450arom support and expand the observations reported in germ cells of other mammalian species. Therefore, female hormones (or the ratio androgens/estrogens) do play a role, either directly on germ cells or via testicular somatic cells, in the maintenance of male gonadal functions. Several steps, including spermatid production, the sperm maturation and/or survival provide opportunity for estrogen action.