Résumé
A novelpaired-like homeobox gene, designatedEsx1,was isolated in a screen for homeobox genes that regulate mouse embryogenesis. Analysis of a mouse interspecific backcross panel demonstrated thatEsx1mapped to the distal arm of the X chromosome. During embryogenesis,Esx1expression was restricted to extraembryonic tissues, including the endoderm of the visceral yolk sac, the ectoderm of the chorion, and subsequently the labyrinthine trophoblast of the chorioallantoic placenta. In adult tissues,Esx1expression was detected only in testes. However,Esx1transcripts were not detected in the testes of sterileW/Wvmice, suggesting thatEsx1expression is restricted to male germ cells.In situhybridization experiments of testes indicated thatEsx1transcripts were most abundant in pre- and postmeiotic germ cells. Hybridization experiments suggested thatEsx1was conserved among vertebrates, including amphibians, birds, and mammals. During mouse development, the paternally derived X chromosome is preferentially inactivated in extraembryonic tissues of XX embryos, including the trophoblast, visceral endoderm, and parietal endoderm. In addition, the X chromosome is transiently inactivated during the meiotic stages of spermatogenesis. Thus, the identification ofEsx1provides a molecular entry point into a genetic pathway to understand X chromosome-regulated fetal–maternal interactions and male germ cell development.