Testicular chromatin activation in hypophysectomized rats.

Area of Science:

• Reproductive Biology
• Molecular Endocrinology
• Biochemistry

Background:

• Hypophysectomy in rats leads to decreased testicular activity.
• Hormonal regulation of testicular DNA synthesis and gene expression is crucial for reproduction.

Purpose of the Study:

• To investigate the effects of testosterone propionate and chorionic gonadotrophin on testicular DNA synthesis and polymerase activity in hypophysectomized rats.
• To elucidate the mechanisms by which androgens influence DNA replication and gene expression at the molecular level.

Main Methods:

• Administration of testosterone propionate and chorionic gonadotrophin to hypophysectomized rats.
• Measurement of thymidine incorporation into testicular DNA.
• Assay of DNA polymerase and RNA polymerase activities.
• Analysis of chromatin templating activity and protein phosphokinase activity.

Main Results:

• Hormone treatment increased thymidine incorporation and DNA polymerase activity, with a peak in cytoplasmic DNA polymerase.
• Testicular RNA polymerase and chromatin templating activity increased, primarily due to more initiation sites.
• Nuclear polymerase I responded rapidly, while polymerase II was slower.
• In vivo phosphorylation of chromosomal phosphoproteins and protein phosphokinase activity showed distinct temporal patterns.

Conclusions:

• Testosterone and gonadotrophins stimulate testicular DNA synthesis and gene expression in hypophysectomized rats.
• The observed effects are mediated by increased DNA polymerase activity and enhanced chromatin templating, particularly at initiation sites.
• Distinct temporal responses of different polymerases and phosphorylation events suggest complex regulatory mechanisms.