X-chromosome activity in preimplantation mouse embryos from XX and XO mothers.
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.
D000228:Adenine Phosphoribosyltransferase / Q000378:metabolism; D000818:Animals; D001755:Blastocyst / Q000201:enzymology; D004622:Embryo, Mammalian / Q000201:enzymology*; D005260:Female; D007041:Hypoxanthine Phosphoribosyltransferase / Q000378:metabolism*; D007621:Karyotyping; D051379:Mice; D012730:Sex Chromosomes / Q000502:physiology*; D013997:Time Factors; D014960:X Chromosome / Q000502:physiology*
D000228:Adenine Phosphoribosyltransferase; D007041:Hypoxanthine Phosphoribosyltransferase