Random X-chromosome inactivation in female primordial germ cells in the mouse

J Embryol Exp Morphol. 1981 Aug;64:251-8.


The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from 12 1/2-day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1). If such germ cells carry the preferentially active Searle's translocated X chromosome (Lyon, Searle, Ford & Ohno, 1964), then only the Pgk-1 allele on this chromosome is expressed. This confirms Johnston's evidence (1979, 1981) that Pgk-1 expression reflects a single active X chromosome at this time. Extracts of 12 1/2-day germ cells from heterozygous females carrying two normal X chromosomes show both the A and the B forms of PGK; since only one X chromosome in each cell is active, different alleles must be expressed in different cells, suggesting that X-chromosome inactivation is normally random in the germ line. This result makes it unlikely that germ cells are derived from the yolk-sac endoderm where the paternally derived X chromosome is preferentially inactivated. In their pattern of X-chromosome inactivation, germ cells evidently resemble other tissues derived from the epiblast.

MeSH terms

  • Animals
  • Female
  • Gene Expression Regulation*
  • Heterozygote
  • Isoenzymes / genetics*
  • Mice
  • Ovum / ultrastructure*
  • Phosphoglycerate Kinase / genetics*
  • Sex Chromosomes / enzymology*
  • X Chromosome / enzymology*
  • Yolk Sac / enzymology


  • Isoenzymes
  • Phosphoglycerate Kinase