X Chromosome Inactivation, XIST, and Pursuit of the X-Inactivation Center

摘要: In addition to defining the murine XIC, current study provides intriguing glimpses into mode of action Xist RNA itself. The authors describe an apparent third state expression in ES cells. Two states were observed previously: one, completely repressed differentiated male cells and on active X female or, two, expressed at high levels from inactive chromosome cells, with coating close association DNA (Clemson et al. 1996xClemson, C.M, McNeil, J.A, Willard, H, Lawrence, J.B. J. Cell Biol. 1996; 132: 1–17Crossref | PubMed Scopus (453)See all ReferencesClemson 1996). these two states, Jaenisch's group reports here a promised future manuscript that is low undifferentiated chromosomes forming local site over but not spreading along X. This suggests that, both prior time inactivation while genetically active, are “preinactivation” distinguishable after (Figure 1Figure 1).This finding, which will require confirmation early mouse embryos, has important implications for inactivation, since it XIC X-inactivation process itself have effect chromosomes. One proposed functions been count number by interacting autosomal factor “blocks” be prevents occurring (11xLyon, M.F. Nature. 379: 116–117Crossref (37)See References, 14xRastan, S. Embryol. Exp. Morphol. 1983; 78: 1–22PubMedSee References). While paper does directly support or refute this widely quoted model, possible function blocking as trans-acting repressor Xist, down-regulating detected differentiation “preactive” preventing dramatic up-regulation precedes “preinactive” X.The finding Lee their transgenes, cell differentiation, express coat autosome transgenes inserted integral part process. availability system evaluate its impact gene either endogenous reporter genes should hasten screening informative mutants do spread (or both).The pursuit detailed understanding followed long arduous path. Hopefully, new approaches manipulate XIST/Xist culture transgenic knockout mice, wait answers end path long. As such become available, possible, fullness time, dissect different components process, understand molecular interactions, determine genetic developmental control.