Aromatase activity has been measured in Leydig cells and Sertoli cells from both immature and mature rats. Cytochrome P450 aromatase (P450arom) has been immunolocalized in germ cells of the rodent, bear, and rooster. Our purpose was to investigate expression of and to immunolocalize P450arom in adult rat testicular cells. After Western blotting with a specific anti-cytochrome P450arom antibody, we demonstrated the presence of a 55-kDa protein in mature rat seminiferous tubules and crude germ cell preparations. Immunoreactive aromatase was detected both in cultured rat Leydig cells and in testis sections (interstitial tissue and elongated spermatids showed positive immunoreactivity for P450arom). We next used reverse transcription-polymerase chain reaction to localize and quantify the P450arom mRNA in the various testicular cells. In rat Leydig cells, the amount of P450arom mRNA was 15 times higher than in Sertoli cells (34.1+/-3.2 to 2.3 +/-0.2 x 10(-3) amol/10(6) cells, respectively). In pachytene spermatocytes, round spermatids, and testicular spermatozoa the P450arom mRNA levels were 38.7+/-8.1, 20.4+/-3.8, and < 1.3 x 10(-3) amol/10(6) cells, respectively. The aromatase activity was 2.5-4 times higher in testicular spermatozoa (8.48+/-1.98 fmol/10(6) cells per hour) than in other germ cells. These results indicate that in mature rats, not only Leydig cells and Sertoli cells but also germ cells have the capacity to express functional P450arom. According to the germ cell maturation state, there was an inverse relationship between P450arom mRNA content and the biological activity of the protein. The expression of the functional P450arom in mature rat germ cells confirms the existence of an additional source of estrogens within the genital tract of the male.

The cytochrome P450 aromatase (P450arom) is the terminal enzyme responsible for the irreversible transformation of androgens into oestrogens and is present in the endoplasmic reticulum of various tissues throughout at least the phylum of vertebrates. The CYP 19 gene is unique and its expression is regulated in a tissue and more precisely in a cell-specific fashion via the alternative use of several promoters located in the first exons. The P450arom has been immunolocalized in germ cells of the mouse, brown bear and rooster. According to age, aromatase activity has been measured in immature and mature rat Leydig cells as well as in Sertoli cells, whereas in the pig, ram and human aromatase is mainly present in Leydig cells. In the adult rat testis, four complementary approaches (RTPCR, in situ hybridization, immunocytochemistry and the tritiated water assay) demonstrate that not only somatic cells but also mature germ cells represent a source of oestrogen synthesis. Taking into account the widespread distribution of oestrogen receptors (ER alpha & ER beta) in testicular cells and the genital tract of the male on the one hand, and the cross-talk between sex steroids and growth factors, and between membrane receptors and nuclear receptors for steroids on the other hand, it is anticipated that understanding of the pathophysiological roles of these 'female' hormones in the male will advance understanding of the hormonal regulation of male reproductive function. One of the future goals is to define oestrogen-targeted genes in the male gonad and indeed, a lot of work is now focused on this specific area in order to clarify the role of oestrogens in the reproductive tract of the male as well as to elucidate the regulation of aromatase gene expression.

Spermatogenesis is a process that involves an array of cellular and biochemical events, collectively culminating in the formation of haploid spermatids from diploid precursor cells known as spermatogonia. As germ cells differentiate from spermatogonia into elongated spermatids, they also progressively migrate across the entire length of the seminiferous epithelium until they reach the luminal edge in anticipation of spermiation at late stage VIII of spermatogenesis. At the same time, these germ cells must maintain stable attachment with Sertoli cells via testis-unique intermediate filament-(i.e. desmosome-like junctions) and actin-(i.e. ectoplasmic specializations, ESs) based cell junctions to prevent sloughing of immature germ cells from the seminiferous epithelium, which may result in infertility. In essence, both desmosome-like junctions and basal ESs are known to coexist between Sertoli cells at the level of the blood -testis barrier where they cofunction with the well-studied tight junction in maintaining the immunological barrier. However, the type of anchoring device that is present between Sertoli and germ cells depends on the developmental stage of the germ cell, i.e. desmosome-like junctions are present between Sertoli and germ cells up to, but not including, step 8 spermatids after which this junction type is replaced by the apical ES. While little is known about the biology of the desmosome-like junction in the testis, we have a relatively good understanding of the molecular architecture and the regulation of the ES. Here, we discuss recent findings relating to these two junction types in the testis, highlighting prospective areas that should be investigated in future studies.

No abstract

No abstract

No abstract

No abstract

No abstract