Loss of spermatogonia and wide-spread DNA methylation defects in newborn male mice deficient in DNMT3L

Background: Formation of haploid spermatozoa capable of fertilization requires proper programming of epigenetic information. Exactly how DNMT3L (DNA methyltransferase 3-Like), a postulated regulator of DNA methyltransferase activity, contributes to DNA methylation pattern acquisition during gametogenesis remains unclear. Here we report on the role of DNMT3L in male germ cell development. Results: A developmental study covering the first 12 days following birth was conducted on a Dnmt3L mutant mouse model; lower germ cell numbers and delayed entry into meiosis were observed in Dnmt3L(-/-) males, pointing to a mitotic defect. A temporal expression study showed that expression of Dnmt3L is highest in prenatal gonocytes but is also detected and developmentally regulated during spermatogenesis. Using a restriction enzyme qPCR assay (qAMP), DNA methylation analyses were conducted on postnatal primitive type A spermatogonia lacking DNMT3L. Methylation levels along 61 sites across chromosomes 4 and X decreased significantly by approximately 50% compared to the levels observed in Dnmt3L(+/+) germ cells, suggesting that many loci throughout the genome are marked for methylation by DNMT3L. More so, hypomethylation was more pronounced in regions of lower GC content than in regions of higher GC content. Conclusion: Taken together, these data suggest that DNMT3L plays a more global role in genomic methylation patterning than previously believed.