Satomi Kuramochi‐Miyagawa1, Toshiaki Watanabe2, Kengo Gotoh3, Yasushi Totoki4, Atsushi Toyoda4, Masahito Ikawa3, Noriko Asada3, Kanako Kojima3, Yuka Yamaguchi3, Takashi W. Ijiri5, Kenichiro Hata2, En Li6, Yoichi Matsuda5, Tohru Kimura3, Masaru Okabe3, Yoshiyuki Sakaki4, Hiroyuki Sasaki2, Toru Nakano6,3
1Department of Pathology, Medical School, Graduate School of Frontier Biosciences, Research Institute for Microbial Diseases, Osaka University, Yamada-oka 2-2 Suita, Osaka 565-0871, Japan.
2Research Organization of Information and Systems, National Institute of Genetics Mishima
3Osaka University
4RIKEN
5Hokkaido University
6Novartis, USA
Tóm tắt
Silencing of transposable elements occurs during fetal gametogenesis in males via de novo DNA methylation of their regulatory regions. The loss of MILI (miwi-like) and MIWI2 (mouse piwi 2), two mouse homologs of Drosophila Piwi, activates retrotransposon gene expression by impairing DNA methylation in the regulatory regions of the retrotransposons. However, as it is unclear whether the defective DNA methylation in the mutants is due to the impairment of de novo DNA methylation, we analyze DNA methylation and Piwi-interacting small RNA (piRNA) expression in wild-type, MILI-null, and MIWI2-null male fetal germ cells. We reveal that defective DNA methylation of the regulatory regions of the Line-1 (long interspersed nuclear elements) and IAP (intracisternal A particle) retrotransposons in the MILI-null and MIWI2-null male germ cells takes place at the level of de novo methylation. Comprehensive analysis shows that the piRNAs of fetal germ cells are distinct from those previously identified in neonatal and adult germ cells. The expression of piRNAs is reduced under MILI- and MIWI2-null conditions in fetal germ cells, although the extent of the reduction differs significantly between the two mutants. Our data strongly suggest that MILI and MIWI2 play essential roles in establishing de novo DNA methylation of retrotransposons in fetal male germ cells.
