Alterations of DNA methylation patterns in germ cells and Sertoli cells from developing mouse testis

In situ alterations of DNA methylation were studied between 14 d postcoitum and 4 d postpartum in Sertoli cells and germ cells from mouse testis, usin g anti-5-methylcytosine antibodies. Compared to cultured fibroblasts, Serto li cells display strongly methylated juxtacentromeric heterochromatin, but hypomethylated chromatids. Germ cells always possess hypomethylated heteroc hromatin, whereas their euchromatin passes from a demethylated to a strongl y methylated status between days 16 and 17 postcoitum. This hypermethylatio n occurs in the absence of DNA replication, germ cells being blocked in the G(0)-G(1) phase from day 15 postcoitum to birth. The DNA hypermethylation of germ cells is maintained until birth and could be visualized on both chr omatids of metaphase chromosomes at the first postpartum cell division. Sub sequently, the DNA hypermethylation is lost semiconservatively, being repla ced by a methylation pattern recalling the typical fibroblast pattern. Thes e alterations of DNA methylation follow a strict chronology, are chromosome structure and cell-type de pendent, and may underlie profound changes of g enome function. Copyright (C) 2000 S. Karger AG, Basel.