title: Fragile (X) expression: relationship to the cell cycle.
abstract: The fragile (X) chromosome demonstrable in individuals with one type of X-linked mental retardation is seldom, if ever, seen in more than 50% of cells of affected individuals. We have devised a model to explain this apparent 50% maximum, one essential feature of which is that the fragile (X) will not be seen in cells in their first division in thymidine-depleted media. The validity of our model was tested on lymphoblastoid cell lines from affected males by treating the cells with fluorodeoxyuridine (FUdR) to induce the marker and/or bromodeoxyuridine (BrdU) to determine the cell cycle. We have evidence that the fragile (X) is present in cells in the first and subsequent cell divisions in thymidine-depleted media. In light of these observations our model is not valid and the 50% expression of the fragile site at Xq(28) and other unusual properties of this region of the X chromosome remain unexplained.
mesh_terms: D001483:Base Sequence; D001973:Bromodeoxyuridine; D002453:Cell Cycle; D002871:Chromosome Banding; D005467:Floxuridine; D005600:Fragile X Syndrome / Q000235:genetics* / Q000473:pathology; D006801:Humans; D007621:Karyotyping; D008214:Lymphocytes / Q000166:cytology; D008297:Male; D008957:Models, Genetic; D012729:Sex Chromosome Aberrations / Q000235:genetics*
chemical_list: D005467:Floxuridine; D001973:Bromodeoxyuridine