FIGURE 9-50 The Xist long noncoding RNA encoded in the X-inactivation center coats the inactive X chromosome in cells of mammalian females, repressing transcription of most genes on the inactive X. (a) The region of the human X-inactivation center encoding the noncoding RNAs Xist (transcribed from the inactive X), and Tsix (transcribed from the active X). Numbers are base pairs from the left end of the X chromosome. (b) A cultured fibroblast from a human female was analyzed by in situ hybridization with a probe complementary to Xist RNA labeled with a red fluorescent dye (left), a chromosome paint set of probes for the X chromosome labeled with a green fluorescent dye (center), and an overlay of the two fluorescent micrographs. The condensed inactive X chromosome is associated with Xist RNA. (c) Model for the spreading of the Xist lncRNA-protein complex on the inactive X chromosome during early differentiation of female embryonic stem cells. See E. Heard and A.-V. Gendrel, 2014, Annu. Rev. Cell Dev. Biol. 30:561. (d) Proteins associated with Xist lncRNA. Question marks indicate that it is not yet known how PRC2 complexes associate with HDAC3 and the RNA-binding protein SHARP. See C. A. McHugh et al., 2015, Nature 521:232.