Non‐random X‐chromosome expression early in mouse development

Abstract

AbstractWe have used a sensitive electrophoretic technique for estimating the activity, or ratio, of two allozymes of the X‐chromosome‐linked enzyme phosphoglycerate kinase (PGK‐1), in order to investigate the randomness of X‐chromosome expression in the derivatives of the three primary cell lineages of the early mouse conceptus. The maternally derived Pgk‐1 allele is preferentially expressed in the derivatives of the primitive endoderm and trophectoderm lineages at 6 1/2 days post coitum in Pgk‐1a/Pgk‐1b heterozygous conceptuses, and in the one informative 5 1/2‐day heterozygous conceptus analysed. This evidence for preferential expression of the maternally derived X chromosome (Xm), so soon after the time of X‐chromosome inactivation, favors the possibility that the preferential expression of Xm is a consequence of primary non‐random X‐chromosome inactivation, rather than a secondary selection phenomenon. The majority of embryos analysed at 4 1/2 and 5 1/2 days pc produced only a single PGK‐1 band, corresponding to the allozyme produced by the Pgk‐1 allele on Xm, although 50% of these embryos should have been heterozygous females. Possible explanations are discussed.