Random X-chromosome inactivation in female primordial germ cells in the mouse.
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.
D000818:Animals; D005260:Female; D005786:Gene Expression Regulation; D006579:Heterozygote; D007527:Isoenzymes / Q000235:genetics*; D051379:Mice; D010063:Ovum / Q000648:ultrastructure*; D010735:Phosphoglycerate Kinase / Q000235:genetics*; D012730:Sex Chromosomes / Q000201:enzymology*; D014960:X Chromosome / Q000201:enzymology*; D015017:Yolk Sac / Q000201:enzymology
D007527:Isoenzymes; D010735:Phosphoglycerate Kinase