ESX1, A NOVEL X-CHROMOSOME-LINKED HOMEOBOX GENE EXPRESSED IN MOUSE EXTRAEMBRYONIC TISSUES AND MALE GERM-CELLS

A novel paired-like homeobox gene, designated Esx1, was isolated in a screen for homeobox genes that regulate mouse embryogenesis. Analysis of a mouse interspecific backcross panel demonstrated that Esx1 mapped to the distal arm of the X chromosome. During embryogenesis, Esx1 exp ression was restricted to extraembryonic tissues, including the endode rm of the visceral yolk sac, the ectoderm of the chorion, and subseque ntly the labyrinthine trophoblast of the chorioallantoic placenta. In adult tissues, Esx1 expression was detected only in testes. However, E sx1 transcripts were not detected in the testes of sterile W/W-v mice, suggesting that Esx1 expression is restricted to male germ cells. In situ hybridization experiments of testes indicated that Esx1 transcrip ts were most abundant in pre- and postmeiotic germ cells. Hybridizatio n experiments suggested that Esx1 was conserved among vertebrates, inc luding amphibians, birds, and mammals. During mouse development, the p aternally derived X chromosome is preferentially inactivated in extrae mbryonic tissues of XX embryos, including the trophoblast, visceral en doderm, and parietal endoderm. In addition, the X chromosome is transi ently inactivated during the meiotic stages of spermatogenesis. Thus, the identification of Esx1: provides a molecular entry point into a ge netic pathway to understand X chromosome-regulated fetal-maternal inte ractions and male germ cell development. (C) 1997 Academic Press.