Chromosomal basis of X chromosome inactivation: identification of a multigene domain in Xp11.21-p11.22 that escapes X inactivation.
A number of genes have been identified that escape mammalian X chromosome inactivation and are expressed from both active and inactive X chromosomes. The basis for escape from inactivation is unknown and, a priori, could be a result of local factors that act in a gene-specific manner or of chromosomal control elements that act regionally. Models invoking the latter predict that such genes should be clustered in specific domains on the X chromosome, rather than distributed at random along the length of the X. To distinguish between these possibilities, we have constructed a transcription map composed of at least 23 distinct expressed sequences in an approximately 5.5-megabase region on the human X chromosome spanning Xp11.21-p11.22. The inactivation status of these transcribed sequences has been determined in a somatic cell hybrid system and correlated with the position of the genes on the physical map. Although the majority of transcribed sequences in this region are subject to X inactivation, eight expressed sequences (representing at least six different genes) escape inactivation, and all are localized to within a region of less than 370 kb. Genes located both distal and proximal to this cluster are subject to inactivation, thereby defining a unique multigene domain on the proximal short arm that is transcriptionally active on the inactive X chromosome.
Department of Genetics and Center for Human Genetics, Case Western Reserve University School of Medicine and University Hospitals of Cleveland, Cleveland, OH 44106, USA. andrew_miller@sequana.com
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Miller
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Willard
D000818:Animals; D002874:Chromosome Mapping; D004303:Dosage Compensation, Genetic; D006801:Humans; D006822:Hybrid Cells; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D014158:Transcription, Genetic; D014960:X Chromosome