X-chromosome activity in preimplantation mouse embryos from XX and XO mothers

J Embryol Exp Morphol. 1978 Aug;46:53-64.


Embryos from XO female mice begin development with half the activity levels of an enzyme (HPRT) coded for by a gene on the X chromosome, compared with embryos from XX females. Groups of unfertilized eggs and individual embryos at the 8-cell, morula and blastocyst stages were assayed for HPRT activity. An autosomally coded enzyme (APRT) was assayed simultaneously in the same reaction mix as a control. There is a substantial increase in HPRT activity by the 8-cell stage. However, the mean activity of HPRT in embryos of XO mothers remains half that in embryos of XX mothers. This suggests a significant maternally inherited component of HPRT activity in 8-cell embryos. By the 9- to 16-cell morula stage the HPRT activities in the two groups of embryos become similar due, presumably, to a transition to embryo-coded activity; HPRT activities in individual morulae from XX mothers show a bimodal distribution consistent with the hypothesis that both X-chromosomes are active in XX embryos at this stage.

Publication types

  • Comparative Study

MeSH terms

  • Adenine Phosphoribosyltransferase / metabolism
  • Animals
  • Blastocyst / enzymology
  • Embryo, Mammalian / enzymology*
  • Female
  • Hypoxanthine Phosphoribosyltransferase / metabolism*
  • Karyotyping
  • Mice
  • Sex Chromosomes / physiology*
  • Time Factors
  • X Chromosome / physiology*


  • Adenine Phosphoribosyltransferase
  • Hypoxanthine Phosphoribosyltransferase