Fig. 4

A speculative model of Xist function. The central part of the diagram shows a nucleus, with the active (Xa) and the inactive (Xi) chromosomal territories highlighted in green and yellow, respectively (gray indicates the chromosomal territories of other chromosomes). Magnified views of the Xi (right) and the Xa (left) territories are shown. The following model is based on the observations of Smeets and colleagues [25]. Coating with Xist RNA might cause a collapse of open chromatin channels, and this, in turn, might block the access of transcription factors and RNA polymerase II (RNA Pol II) to gene-regulatory elements. Alternatively, Xist might compete with C0t-1 RNA, and removal of this class of RNA could, in turn, lead to chromosome compaction [68]