Expression of X-linked phosphoglycerate kinase in early mouse embryos homozygous at the Xce locus

The expression of maternally derived X-chromosomal Pgk-1 alleles was investigated in oocytes and early embryos of mice carrying different alleles (Xcea, Xcec) of the X-chromosome controlling element (Xce) locus. Pgk-1 allelic expression was determined by measuring their gene products using Cellogel electrophoresis and a sensitive fluorimetric enzyme assay. In addition to the already existing mouse strain of the genotypes Pgk-1a Xcec and Pgk-1b Xcea, a new line was bred carrying the combination Pgk-1b Xcec. The X chromosomes carrying the combinations Pgk-1a Xcec and Pgk-1b Xcec were of feral origin, whereas Pgk-1b Xcea was derived from a laboratory line. Our results using Xcec homozygous females confirm that maternal Pgk-1 is already expressed on day 4 of embryogenesis, thus substantiating data previously obtained using Xcea/Xcec heterozygous females. This finding also demonstrates that the timing of reactivation of maternal Pgk-1 is not influenced by the Xce locus. Furthermore, we found that oocytes from Xcec homozygous females have a balanced PGK-1 A/PGK-1 B allozyme ratio (50:50), whereas in oocytes obtained from Xcea/Xcec heterozygotes, the PGK-1 allozyme ratio is about 60:40. In tissues of adult Xce homozygous females, the PGK-1 allozymes are also balanced, whereas in Xcea/Xcec heterozygous females, the ratio is about 35:65. In addition to the relative activity of the PGK-1 allozymes, we also measured the absolute activity of PGK-1 in oocytes obtained from three types of Xce homozygous females.(ABSTRACT TRUNCATED AT 250 WORDS)