DEVELOPMENTAL AND HORMONAL-REGULATION OF DNA METHYLTRANSFERASE IN THE RAT TESTIS

Changes in DNA methylation patterns during gametogenesis have been implicated in the regulation of germ cell development and genomic imprinting. Cytosine methylation is catalyzed by the enzyme DNA (cytosine-5)-methyltransferase (DNA MTase). The objective of this study was to determine the presence and study the developmental and hormonal regulation of DNA MTase expression in the rat testis. Northern blots of RNA isolated from 10 different adult rat tissues mere used to determine tissue-specific differences in transcript size and abundance of DNA MTase. The developmental regulation of DNA MTase in the rat testis was examined by use of Northern blots of testicular and isolated germ cell RNA from rats ranging in age from 7 to 91 days. For a better understanding of the hormonal regulation of DNA MTase in the rat testis, adult rats were hypophysectomized and 4 wk later (Day 0) received 24-cm testosterone silastic implants; controls were sham hypophysectomized. At Days 0, 3, 7, 14, 28, and 56, one testis from each rat (n = 4/group) was used to prepare total RNA. Examination of DNA MTase mRNA expression in different rat tissues demonstrated the existence of a single 5.2-kb transcript; up to 5-fold tissue-specific variations in the levels of DNA MTase mRNA between the tissue with the highest expression, spleen, and that with the lowest expression, prostate; and significant levels of expression in the testis (three times prostate levels). During testicular development, DNA MTase mRNA levels were highest at 7-21 days of age and decreased by 45% by Day 28; mRNA levels decreased further to reach steady adult levels by Day 42. In the adult testis, DNA MTase mRNA and protein were detected in isolated round spermatids; in contrast, DNA MTase was not expressed in pachytene spermatocytes or residual bodies. DNA MTase mRNA levels were highest (4-fold sham values) at 0 days and decreased by 50% after 28 days of testosterone administration; steady adult levels were reached after 56 days of testosterone treatment. In conclusion, DNA MTase expression is developmentally regulated both during the initiation of spermatogenesis in young rats and during the hormonal restoration of germ cells in hypophysectomized adult rats.