Methylation of unique sequence DNA during spermatogenesis in mice.

In order to study whether changes in methylation of unique sequence DNA were related to meiosis, DNA was purified from F9 embryonal carcinoma (a "primordial germ cell" equivalent), germ cells from immature testes (containing germ cells up to early spermatocytes), sperm, and appropriate somatic tissues. Restriction was performed with the isoschizomers Msp I and Hpa II, and Eco RI as a control. Electrophoresis and Southern transfers were followed by hybridization to a mouse major beta-globin clone (f7), a mouse pancreatic amylase clone (pMPa21), a type I, histocompatibility-2 clone (pH-2D-4), and a spermatid cDNA clone (pPM 459). The variably methylated sites were all hypomethylated in the embryonal carcinoma DNA and hypermethylated in DNA from immature testes and sperm, irrespective of the transcription state of the gene. The pattern in control tissues generally conformed to an inverse correlation of methylation with transcription. These results suggest that hypermethylation of sperm DNA persists from hypermethylation of these sequences early in testicular development, independent of gene expression.