title: Studies of the temporal relationship between the cytogenetic and biochemical manifestations of X-chromosome inactivation during the differentiation of LT-1 teratocarcinoma stem cells.
abstract: Previous biochemical studies have suggested that both X chromosomes produce gene products when cells of the LT-1 teratocarcinoma stem cell line are maintained in the undifferentiated state, and that dosage compensation, the biochemical manifestation of X inactivation, occurs when the cells are induced to differentiate in vitro (Martin et al., 1978). In this study the differentiation of LT-1 cells in vitro is described in detail, and data from cytogenetic studies of the time of X-chromosome replication in LT-1 cells are presented. They show that as long as the cells are maintained in the undifferentiated state both X chromosomes in each cell show the isocyclic replication pattern typical of a genetically active chromosome. However, when the LT-1 cells are induced to differentiate under appropriate conditions, one of the two X chromosomes in each cell of a large proportion of the population displays the allocyclic (either early or late) replication pattern typical of an inactive X chromosome. These data thus confirm that undifferentiated LT-1 cells contain two active X chromosomes and that X inactivation occurs in differentiating cultures of LT-1 cells. It is further demonstrated that there is a close temporal correlation between the biochemical and cytogenetic manifestations of the X-inactivation process. In addition, we observed that although X inactivation does not occur in the absence of morphological differentiation, it does not always occur when the cells differentiate in vitro.
mesh_terms: D000818:Animals; D001973:Bromodeoxyuridine; D002454:Cell Differentiation; D002460:Cell Line; D002871:Chromosome Banding; D004261:DNA Replication; D004303:Dosage Compensation, Genetic; D004707:Endoderm / Q000166:cytology; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D008677:Metaphase; D051379:Mice; D008856:Microscopy, Fluorescence; D010734:Phosphogluconate Dehydrogenase / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology; D013724:Teratoma / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D013997:Time Factors; D014960:X Chromosome / Q000378:metabolism
chemical_list: D010734:Phosphogluconate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D001973:Bromodeoxyuridine