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We have analysed Xist expression patterns in parthenogenetic and control fertilised preimplantation embryos by using RNA FISH. In normal XX embryos, maternally derived Xist alleles are repressed throughout preimplantation development. Paternal alleles are expressed as early as the 2-cell stage. In parthenogenetic embryos, we observed Xist RNA expression and accumulation from the morula stage onwards, indicating loss of maternal imprinting. In the majority of cells, expression was from a single allele, indicating that X chromosome counting occurs to establish appropriate monoallelic Xist expression. We discuss these data in the context of models for regulation of imprinted and random X inactivation.

Original publication




Journal article


Dev Biol

Publication Date





343 - 350


Alleles, Animals, Blastocyst, DNA, Fathers, Female, Genomic Imprinting, In Situ Hybridization, Fluorescence, Male, Mice, Mice, Inbred C57BL, Mice, Inbred CBA, Models, Genetic, Mothers, Phenotype, RNA, Time Factors, X Chromosome