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Regulation of testicular proopiomelanocortin gene expression
Abstract:
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.
Insights
Testicular POMC-like mRNA expression increases significantly during rat development and is regulated by gonadotropins, not glucocorticoids, differing from pituitary regulation.
Area of Science:
- Reproductive Endocrinology
- Molecular Endocrinology
- Gene Expression Regulation
Background:
- Pro-opiomelanocortin (POMC) gene is expressed in testicular Leydig cells, producing a shorter POMC-like mRNA compared to the pituitary.
- Understanding the developmental and regulatory patterns of this testicular POMC-like mRNA is crucial for comprehending Leydig cell function.
Purpose of the Study:
- To define the ontogeny (developmental pattern) of POMC gene expression in the rat testis.
- To investigate the regulatory mechanisms influencing testicular POMC-like mRNA levels, specifically the roles of gonadotropins and glucocorticoids.
Main Methods:
- Quantification of POMC-like mRNA in rat testes at various developmental ages (15, 20, 25, 40 days).
- Experimental manipulation involving hypophysectomy and human chorionic gonadotropin (hCG) administration to assess hormonal regulation.
- Evaluation of POMC-like mRNA levels following adrenalectomy to examine glucocorticoid influence.
Main Results:
- Testicular POMC-like mRNA levels were low in young rats, dramatically increasing between 20-25 days and peaking at 40 days.
- Hypophysectomy decreased testicular weight and POMC-like mRNA; hCG treatment prevented this decline and increased mRNA levels.
- Glucocorticoid deprivation (adrenalectomy) did not affect testicular POMC-like mRNA, unlike in the pituitary.
Conclusions:
- The ontogeny of testicular POMC gene expression closely parallels Leydig cell maturation and LH receptor development.
- Gonadotropins (LH/hCG) are key regulators of testicular POMC-like mRNA expression.
- Glucocorticoids do not appear to be primary regulators of POMC-like mRNA in the testis, indicating differential regulation compared to the pituitary.