Studies on Metatherian Sex Chromosomes VII. Glucose-6-phosphate Dehydrogenase Expression in Tissues and Cultured Fibroblasts of Kangaroos

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Abstract
Expression of the sex-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) was examined electrophoretically in tissues and cultured fibroblasts of female kangaroo heterozygotes ranging in age from 26 days to adult. All tissues expressed only the maternally derived allele irrespective of which allele was maternal or paternal in origin. Cultured fibroblasts derived from these same heterozygotes displayed unique G6PD phenotypes not found in the living animal. These phenotypes consist of a broad band which either completely or partially overlaps the allozymes produced by the maternally and paternally derived alleles. In vitro hybridization of G6PD from species showing greater differences in electrophoretic mobility indicate that G6PD is a dimer in marsupials. The cultured fibroblast G6PD phenotypes are consistent with different proportions of homodimer and heterodimer formation. The appearance of the heterodimer indicates that both alleles are active within 1 cell. This is reinforced by the finding that clones from cultured fibroblasts of 1 of the heterozygotes had an identical phenotype to that of the mass culture from which the clones were derived. Some heterozygotes apparently express both Gpd alleles equally in each cultured fibroblast while other heterozygotes show normal activity of the maternally derived allele and partial expression of the paternally derived allele.