<i>De novo</i> methylation in male germ cells of the common marmoset monkey occurs during postnatal development and is maintained <i>in vitro</i>

<p>The timing of <i>de novo</i> DNA methylation in male germ cells during human testicular development is yet unsolved. Apart from that, the stability of established imprinting patterns <i>in vitro</i> is controversially discussed. This study aimed at determining the timing of DNA <i>de novo</i> methylation and at assessing the stability of the methylation status <i>in vitro</i>. We employed the marmoset monkey (<i>Callithrix jacchus</i>) as it is considered the best non-human primate model for human testicular development. We selected neonatal, pre-pubertal, pubertal, and adult animals (n = 3, each) and assessed germ cell global DNA methylation levels by 5-methyl cytosine staining, and <i>Alu</i> elements and gene-specific methylation (<i>H19, LIT1, SNRPN, MEST, OCT4, MAGE-A4</i>, and <i>DDX-4)</i> by pyrosequencing. <i>De novo</i> methylation is progressively established during postnatal primate development and continues until adulthood, a process that is different in most other species. Importantly, once established, methylation patterns remained stable, as demonstrated using <i>in vitro</i> cultures. Thus, the marmoset monkey is a unique model for the study of postnatal DNA methylation mechanisms in germ cells and for the identification of epimutations and their causes.</p