Expression of type II activin receptor genes in the male and female reproductive tissues of the rat.

In addition to the feedback regulation of pituitary FSH secretion, gonadal activins have been shown to modulate physiological functions in the reproductive tissues. These observations suggested that activins and the receptors for these peptides may be coexpressed in gonadal tissues. In this study, we have cloned cDNAs encoding two species of type II activin receptors (ActRII and ActRIIB) from rat testicular mRNA and have shown that the two rat activin receptors share 97% similarity in the nucleotide sequence with those reported in the mouse. Two species [6 and 3 kilobases (kb)] ActRII mRNA were identified in all reproductive tissues of adult male and female rats. The 6-kb ActRII mRNA was the abundant form in most of the reproductive tissues. In placenta, the 6- and 3-kb mRNA were present in equal intensity. Interestingly, the ratio of the expression of two species of ActRII mRNA in rat testis changed with age. The 6-kb mRNA was the predominant form in immature 15- and 20-day-old testis, while the 3-kb mRNA increased with age and became the major form in mature testis. In female rats, however, the 6-kb ActRII mRNA was the abundant species in all of the ovaries examined, including immature, normal cycling, and pregnant rats. One major 2.25-kb species of ActRIIB mRNA was identified in all of the reproductive organs examined. Nucleotide sequence analysis of the isolated ActRIIB cDNA clones revealed that ActRIIB2 was the major isoform found in rat testis. The levels of expression of ActRIIB gene in rat testis or ovary were not changed during development. We conclude that 1) both type II and IIB activin receptor genes are widely expressed in the male and female reproductive tissues; and 2) the expression of 6- and 3-kb ActRII mRNA is tissue dependent as well as age dependent in rat testis.

Expression and regulation of testicular inhibin alpha-subunit gene in vivo and in vitro.

Inhibin, a gonadal peptide, selectively suppresses FSH release from the pituitary. The cDNAs coding for ovarian inhibin have been isolated and characterized. However, little is known about testicular inhibin. In this study we have isolated inhibin alpha-subunit cDNA from human testicular cDNA libraries and determined inhibin alpha-subunit mRNA levels in testes. The longest cDNA isolated from human testis was 1380 nucleotides long and contained a nucleotide sequence identical to that of human placental inhibin alpha-subunit and isolated human inhibin alpha-subunit gene, but different from human ovarian inhibin alpha-subunit in two amino acids in the signal peptide. A single 1.5-kilobase species of inhibin alpha-subunit mRNA was identified in the testes of several species. This mRNA was the same size as those in human ovary and placenta. The regulation of inhibin alpha-subunit mRNA in rat testis was next examined. The concentration of testicular inhibin alpha-subunit mRNA peaked between 20-25 days of age and gradually declined thereafter. Hypophysectomy decreased testicular inhibin alpha-subunit mRNA levels. Supplementation of hypophysectomized animals with FSH restored inhibin alpha-subunit mRNA levels to those in intact controls. By contrast, treatment with testosterone had no effect. Similarly, in Sertoli cell-enriched cultures, FSH, but not testosterone, increased inhibin alpha-subunit mRNA levels. We conclude that 1) human testicular inhibin alpha-subunit mRNA is similar to that of human ovary and placenta; and 2) inhibin alpha-subunit mRNA in Sertoli cells is regulated by FSH, but not testosterone, both in vivo and in vitro.

Regulation of testicular proopiomelanocortin gene expression.

The POMC gene is expressed in testicular Leydig cells, but its mRNA is about 150-200 nucleotides shorter in these cells than in the pituitary. For this reason this testicular mRNA has been termed POMC-like mRNA. The purpose of the present study was to define the ontogeny and regulation of POMC gene expression in rat testis. The level of POMC-like mRNA was very low in the testes of 15- and 20-day-old animals. A dramatic increase in mRNA concentration was observed between 20 and 25 days of age, and maximal levels were detected at 40 days. The ontogeny of testicular POMC gene expression correlates with the reported increases in Leydig cell numbers, immunostainable beta-endorphin in Leydig cells, and testicular LH receptors during development. Since these observations suggested that the expression of testicular POMC gene might be influenced by LH, we studied the effect of hypophysectomy and hCG treatment on testicular POMC-like mRNA. Total contents of testicular RNA and POMC-like mRNA decreased in parallel with the decline of testicular weight after hypophysectomy. Administration of hCG to rats 6 days after hypophysectomy prevented the regression of testes and the decrease in testicular POMC-like mRNA content. An increase in the total amount of testicular POMC-like mRNA was observed relative to that in hypophysectomized controls after 8 days of hCG injection. Similar results were obtained when hCG was administered to rats 13 days after hypophysectomy. The effect of glucocorticoid deprivation on testicular POMC-like mRNA was also studied. The POMC-like mRNA concentration did not increase in testis as it did in the anterior pituitary after adrenalectomy, suggesting that glucocorticoids are not a primary regulator of POMC-like mRNA in the testis. In summary, the ontogeny of expression of testicular POMC gene correlates closely with the maturation pattern of Leydig cells; and the expression of testicular POMC gene is regulated by gonadotropins and not by glucocorticoids. We conclude that the regulation of POMC-like mRNA in the testis is different from that in the pituitary.