Abstract
Considerable evidence suggests that the X inactive transcript gene,XIST/Xist, has a role in the initial steps of X chromosome inactivation in the female mammalian embryo. It is transcribed exclusively from inactive X chromosomes, and its noncoding transcript seems to be essential forcis inactivation. Unexpected for a developmental gene,XIST continues to be expressed in adult somatic cells. To determine the effect of reversal of inactivation on the expression ofXIST, we studied human X chromosomes that had been induced to reverse X inactivation by hybridization of chorionic villi cells from term placentas with mouse A9 cells. In nine hybrids with a reactivated X chromosome,XIST was either not expressed or expressed much less than the locus on the inactive X chromosome in the chorionic villi cells from which they were derived. The repressibility ofXIST by reversal of inactivation in these placental cells mirrors events that occur during the ontogeny of oocytes and indicates that the locus is subject to regulation in somatic cells long after inactivation is established in the embryo. The small residualXIST activity from these active chromosomes suggests that low levels ofXIST expression do not interfere with chromosome activity and raises the possibility that the induction ofcis inactivation requires a certain level ofXIST transcription. The chorionic villi hybrids provide an experimental system to study the developmental regulation ofXIST.
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Luo, S., Torchia, B.S. & Migeon, B.R. XIST expression is repressed when X inactivation is reversed in human placental cells: A model for study ofXIST regulation. Somat Cell Mol Genet 21, 51–60 (1995). https://doi.org/10.1007/BF02255822
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DOI: https://doi.org/10.1007/BF02255822