DXZ4

DXZ4 is a variable number tandemly repeated DNA sequence. In humans it is composed of 3kb monomers containing a highly conserved CTCF binding site. CTCF is a transcription factor protein and the main insulator responsible for partitioning of chromatin domains in the vertebrate genome.
In addition to being enriched in CpG-islands, "DXZ4" transcribes long non-coding RNAs (lncRNAs) and small RNAs of unknown function. Repeat copy number of "DXZ4" is highly polymorphic in human populations (varying between 50 and 100 copies). "DXZ4" is one of many large tandem repeat loci defined as macrosatellites. Several macrosatellites have been described in humans and share similar features, such as high GC content, large repeat monomers, and high variability for repeat copy number within populations. "DXZ4" plays an important role in the unique structural conformation of the inactive X chromosome (Xi) in female somatic cells by acting as a hinge point between two large “super domains”.
In addition to acting as the primary division between domains, "DXZ4" forms long-range interactions with a number of other repeat rich regions along the inactive X chromosome. Knockout of the "DXZ4" locus revealed loss of this structural conformation on the Xi with chromosome wide silencing being maintained.