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Characterization of XIST (inactive X chromosome specific transcripts) in the ovarian carcinoma cell line SKOV3. Cytogenetic studies by spectral karyotyping (top panel) and X chromosome painting (middle panel, green) demonstrated that this cell line has five copies of X chromosomes. RNA FISH showed that the cell line consists of two populations of cells with one or two X chromosomes expressing XIST, respectively (bottom panel, green). Identified in an expression profiling between primary and recurrent ovarian tumors from the same patient, XIST expression was found to be significantly related to the taxol sensitivity in ovarian cancer cell lines and to the disease-free periods of ovarian cancer patients after chemotherapy. For details, see Huang et al. in this issue.