Relationship between the parental origin of theXchromosomes, embryonic cell lineage andXchromosome expression in mice

Abstract

SUMMARYThe electrophoretic variants of theX-chromosome-linked enzyme phosphoglycerate kinase (PGK-1) have been used to investigate the randomness ofXchromosome expression in the fetus and various extra-embryonic membranes of the mouse conceptus. The amnion shows essentially random expression of the maternally derivedXchromosome (Xm) and the paternally derivedXchromosome (Xp). The parietal endoderm, however, shows exclusive or preferential expression ofXm. The results support the idea that the randomness ofXchromosome expression is correlated with embryonic cell lineage such thatXmis preferentially (perhaps exclusively) expressed in derivatives of the primitive endoderm and trophectoderm but thatXmandXpare randomly expressed in the derivatives of the primitive ectoderm.Experiments involving ovary transplants, embryo transfers or crosses with heterozygous mothers confirm previous findings thatXmis preferentially expressed regardless of theXchromosome expressed in the reproductive tract. Additional experiments show that the preferentially expressedXchromosome in the parietal endoderm and visceral yolk sac endoderm of a normalXmXpconceptus is alwaysXmregardless of grand-parental origin ofXmand regardless of whether the mother is a normalXXfemale or anXOfemale.Xpis, however, expressed in these tissues hiXpOfemale conceptuses. It is argued that a form of chromosome imprinting occurs at each generation to markXmandXpas different and that this difference influences the choice of whichXchromosomes are expressed in each cell lineage.