DEVELOPMENTAL EXPRESSION OF DNA METHYLTRANSFERASE MESSENGER-RIBONUCLEIC-ACID, PROTEIN, AND ENZYME-ACTIVITY IN THE MOUSE TESTIS

Sex- and sequence-specific patterns of methylation of mammalian DNA ar e established during gametogenesis and are believed to be important fo r genomic imprinting and developmental gene regulation. DNA methylatio n in mammalian cells is performed predominantly by the enzyme DNA (cyt osine-5)-methyltransferase (DNA MTase). For a better understanding of how DNA methylation events are regulated during spermatogenesis, a dev elopmental study comparing the expression of DNA MTase mRNA, protein, and enzyme activity was performed. Northern and Western blotting and e nzyme activity assays were carried out on testes and purified populati ons of cells from the testes of mice aged 6-70 days. The 5.2-kb DNA MT ase transcript was most abundant in testes of mice aged 6-10 days (2-3 -fold the 70-day values); it had decreased in abundance by 40% by Day 20 and reached steady adult levels by 63 days. On Western blot analysi s, developmental changes in the relative abundance of DNA MTase protei n paralleled the changes seen in mRNA concentrations. DNA MTase enzyme activity in the testis was highest at 6 days of age (10-fold the 70-d ay values); it had decreased by more than 65% by 20 days and reached s teady adult levels at 35 days. Analysis of purified germ cells from th e adult testis revealed high levels of expression of both DNA MTase mR NA and protein in haploid round spermatids. In conclusion, DNA MTase i s clearly developmentally regulated during spermatogenesis at the leve l of mRNA, protein, and enzyme activity. These results argue for an im portant role for this DNA-methylating enzyme during spermatogenesis.