Dynamic methylation pattern of the methyltransferase1o (Dnmt1o) 5 '-flanking region during mouse oogenesis and spermatogenesis

Abstract

DNA methyltransferase1o (Dnmt1o), which is specific to oocyte and preimplantation embryo, plays a role in maintaining DNA methylation in mammalian cells. Here, we investigated the methylation status of CpGs sites in the Dnmt1o 5-flanking region in germ cells at different stages of oogenesis or spermatogenesis. The methylation levels of the CpG sites at the 5-flanking regions were hypermethylated in growing oocytes of all follicular stages, while the oocytes in meiotic metaphase II (MII) were demethylated. The methylation pattern within the CpGs sites in the 5-flanking region, however, was dramatically changed during spermatogenesis. We observed that there was significant non-CpG methylation both in MII oocytes and spermatocytes. Although a low methylation level in non-CpG sites was observed in primary and secondary oocytes, the CpA site of position 25 and CpT site of position 29 within the no-CpG region in the 5-flanking region of Dnmt1o was highly methylated in MII oocytes. During spermatogenesis, the low degree of methylation at CpG sites in spermatocytes increased to a higher degree in sperm, while the high ratio of methylation in non-CpG sites in spermatocytes decreased. Together, germ cells showed inverted methylation patterns between CpG and non-CpG sites in the Dnmt1o 5-upstream region, and the methylation pattern during oogenesis did not drastically change, remaining generally hypomethylated at the MII stage. Mol. Reprod. Dev. 80: 212222, 2013. (c) 2013 Wiley Periodicals, Inc.