The XIST locus is expressed only from the inactive X chromosome, resides at the putative X inactivation center, and is considered a prime player in the initiation of mammalian X dosage compensation. The severe phenotype of human females whose karyotype includes tiny ring X chromosomes has been attributed to the inability of the small ring X chromosome to inactivate. Many of the ring chromosomes lack the XIST locus, consistent with XIST being necessary for cis inactivation. The XIST specific FISH probe is optimized to detect copy numbers of the XIST region at Xq13. The chromosome X Satellite Enumeration (SE X) FISH probe at DXZ1 is added to facilitate chromosome identification.
Migeon et al, 1993, PNAS, 90; 12025-12029.
Jani et al, 1995, Genomics, 27; 182-188.