Journal Article

<i>XIST</i> Expression from the Maternal X Chromosome in Human Male Preimplantation Embryos at the Blastocyst Stage

Pierre F. Ray, Robert M. L. Winston and Alan H. Handyside

in Human Molecular Genetics

Volume 6, issue 8, pages 1323-1327
Published in print August 1997 | ISSN: 0964-6906
Published online August 1997 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/6.8.1323
XIST Expression from the Maternal X Chromosome in Human Male Preimplantation Embryos at the Blastocyst Stage

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In the somatic cells of female mammals, either the maternally or paternally derived X chromosome (XM or XP) is randomly inactivated to achieve dosage compensation for X-linked genes. In early mouse development, however, selective inactivation of XP occurs first in extraembryonic lineages at the blastocyst stage around the time of implantation before later random inactivation in the embryonic ectoderm from which the fetus is derived. Xist, a gene mapping to the X-inactivation centre (Xic), is exclusively expressed from the inactive X-chromosome and is thought to be involved in the initiation of X-inactivation. Consistent with this, Xist is first expressed at the 4-to 8-cell stages, prior to functional inactivation at the blastocyst stage, exclusively from XP in female embryos. This also suggests that genomic imprinting may influence the earliest expression of Xist resulting in selective inactivation of XP and a candidate methylation site in the promoter region has recently been described. Here we report the expression of the human homologue, XIST, in human preimplantation embryos from the 5- to 10-cell stage onwards consistent with its role in the initiation of inactivation. In contrast to the mouse, however, transcripts were detected in both male and female embryos demonstrating XIST expression from the XM in male embryos (XMY).

Journal Article.  3274 words.  Illustrated.

Subjects: Genetics and Genomics

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