FIGURE 1.

Spatial organization of single copy loci by ncRNAs. (A) Transcription of snRNA genes and interaction between intron-encoded snoRNA/snRNAs with coilin mediate Cajal body formation. Cajal bodies associate with sn/snoRNA and histone gene loci and regulate their gene expression. (B) Transcription of an enhancer can produce eRNAs, which associate with the mediator complex and enable chromatin looping, thereby driving enhancer-promoter interaction. (C) In the absence of the ThymoD ncRNA, the enhancer for the BCL11B locus is at nuclear periphery. ThymoD ncRNA mediates enhancer repositioning away from the nuclear periphery and drives chromatin looping of the enhancer bringing it in close proximity to the BCL11B locus, thereby allowing for the transcriptional activation of this locus. (D) In the somatic tissues of placental mammals, Xist lncRNA tethers the inactive X chromosome to the nuclear lamina by interacting with lamin B receptor. Xist interacts with polycomb proteins to establish the heterochromatin state of the inactive X chromosome. Xist also mediates relocation of active genes from the surface of the X chromosome to its interior.