Primary non-random X-inactivation caused by controlling elements in the mouse demonstrated at the cellular level

Abstract

Previous studies have shown that different alleles of the mouse X chromosomal controlling element locus, Xce, cause non-random X-chromosome inactivation as judged by variegation in the coats of female mice heterozygous for X-linked coat colour/structure genes, or Cattanach's translocation (Is (X; 7) Ct), or the relative activity of biochemical variants of the X-linked enzyme PGK. This paper presents evidence using the Kanda differential staining method on 6½ d.p.c. and 13½ d.p.c. female mouse embryos heterozygous for the marker X chromosome Is (X; 7) Ct and carrying different Xce alleles, that the Xce locus affects the randomness of X chromosome inactivation. Furthermore the fact that a marked Xce effect is demonstrable in female embryos as early as 6½ d.p.c. (i.e. very soon after the initial time of X-inactivation) is strong evidence that the Xce locus exerts its effect by causing primary non-random X-inactivation rather than by cell selection after initial random X-inactivation. © 1982, Cambridge University Press. All rights reserved.