DXZ4 is a variable number tandemly repeated

DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...

. In humans it is composed of 3kb monomers containing a highly conserved CTCF binding site. CTCF is a

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

and the main insulator responsible for partitioning of

chromatin Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in r ...

domains in the vertebrate

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

. In addition to being enriched in

CpG-island The CpG sites or CG sites are regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases along its 5' → 3' direction. CpG sites occur with high frequency in genomic regions called CpG isl ...

s, ''DXZ4'' transcribes long non-coding

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

s ( lncRNAs) and

small RNA Small RNA (sRNA) are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA ...

s 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

macrosatellite Macrosatellites are the largest of the tandem DNA repeats. Each macrosatellite repeat typically is several kilobases in length, and the entire repeat array often spans hundreds of kilobases. Reduced number of repeats on chromosome 4 (D4Z4 repeats) ...

s. 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 The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex-d ...

(Xi) in female

somatic cell A somatic cell (from Ancient Greek σῶμα ''sôma'', meaning "body"), or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. Such cells compo ...

s 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.

References

{{reflist Gene expression Repetitive DNA sequences Transcription factors