title: Stability of the "two active X" phenotype in triploid somatic cells.
abstract: We examined triploid cells of XXY karyotype heterozygous for glucose 6 phosphate dehydrogenase (G6PD) electrophoretic variants with regard to the stability of their X chromosome phenotype. Clonal populations of cells derived from these human fibroblasts maintained a precise 1:2:1 ratio of A:heteropolymer:B isozymes throughout their life span, indicating stability of the two active X chromosomes in these cells. To determine the influence of the autosomal complement on X chromosome expression, we attempted to perturb the relationship. Fusion of these triploid cells with human diploid fibroblasts carrying a novel G6PD variant (B') resulted in heterokaryons exprssing a novel heteropolymer, presumably indicating that all three parental X chromosomes were active. However, no derepression of the inactive X chromosome was observed. Analysis of interspecific hybrids derived from triploid cells and mouse fibroblasts confirmed that activity of parental X chromosomes is maintained. Some human mouse hybrid clones, however, expressed only a single human G6PD isozyme, probably attributable to segregation of the pertinent X chromosome, but elimination of a relevant autosome cannot be excluded. The triploid cells transformed by SV40 showed alterations in LDH pattern and an approximately 10-20% decrease in chromosome number, but maintained the precise G6PD phenotype of the untransformed cell. These studies provide evidence for the stability of the X chromosome phenotype in triploid cells.
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic; D002869:Chromosome Aberrations; D002999:Clone Cells / Q000648:ultrastructure; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics; D006579:Heterozygote; D006801:Humans; D006822:Hybrid Cells / Q000648:ultrastructure; D007527:Isoenzymes / Q000235:genetics; D008297:Male; D051379:Mice; D010641:Phenotype; D011123:Polyploidy; D012728:Sex Chromatin / Q000648:ultrastructure; D012730:Sex Chromosomes; D013539:Simian virus 40; D014960:X Chromosome
chemical_list: D007527:Isoenzymes; D005954:Glucosephosphate Dehydrogenase