Submitted May 15, 2007
Returned for revision June 5, 2007
Accepted July 3, 2007
Gamete Biology
Autonomous Regulation of Sex-Specific Developmental Programming in Mouse Fetal Germ Cells
Kazuhiro Iwahashi ,
Hirotaka Yoshioka ,
Eleanor W Low ,
John R McCarrey ,
Ryuzo Yanagimachi ,
and
Yukiko Yamazaki *
* To whom correspondence should be addressed. E-mail: yyamazak{at}hawaii.edu.
Abstract
In mice, unique events regulating epigenetic programming (e.g. genomic imprinting) and replication state (mitosis versus meiosis) occur during fetal germ cell development. To determine whether these processes are autonomously programmed in fetal germ cells or are dependent upon ongoing instructive interactions with surrounding gonadal somatic cells, we isolated male and female germ cells at 13.5 dpc and maintained them in culture for 6 days either alone, or in the presence of feeder cells or gonadal somatic cells. We examined allele-specific DNA methylation in the imprinted H19 and Snrpn genes, and also determined if these cells remained mitotic or entered meiosis. Our results show that isolated male germ cells are able to establish a characteristic "paternal" methylation pattern at imprinted genes in the absence of any support from somatic cells. On the other hand, cultured female germ cells maintain a hypomethylated status at these loci, characteristic of the normal "maternal" methylation pattern in endogenous female germ cells before birth. Further, the surviving female germ cells entered first meiotic prophase and reached the pachytene stage, whereas male germ cells remained mitotic. These results indicate that mechanisms controlling both epigenetic programming and replication state are autonomously regulated in fetal germ cells that have been exposed to the genital ridge prior to 13.5 dpc.
Key words:
Meiosis •
De novo methylation •
Genomic imprinting •
Germ cells •
Sex differentiation
