Escape from X chromosome inactivation is an intrinsic property of the Jarid1c locus.
Although most genes on one X chromosome in mammalian females are silenced by X inactivation, some "escape" X inactivation and are expressed from both active and inactive Xs. How these escape genes are transcribed from a largely inactivated chromosome is not fully understood, but underlying genomic sequences are likely involved. We developed a transgene approach to ask whether an escape locus is autonomous or is instead influenced by X chromosome location. Two BACs carrying the mouse Jarid1c gene and adjacent X-inactivated transcripts were randomly integrated into mouse XX embryonic stem cells. Four lines with single-copy, X-linked transgenes were identified, and each was inserted into regions that are normally X-inactivated. As expected for genes that are normally subject to X inactivation, transgene transcripts Tspyl2 and Iqsec2 were X-inactivated. However, allelic expression and RNA/DNA FISH indicate that transgenic Jarid1c escapes X inactivation. Therefore, transgenes at 4 different X locations recapitulate endogenous inactive X expression patterns. We conclude that escape from X inactivation is an intrinsic feature of the Jarid1c locus and functionally delimit this escape domain to the 112-kb maximum overlap of the BACs tested. Additionally, although extensive chromatin differences normally distinguish active and inactive loci, unmodified BACs direct proper inactive X expression patterns, establishing that primary DNA sequence alone, in a chromosome position-independent manner, is sufficient to determine X chromosome inactivation status. This transgene approach will enable further dissection of key elements of escape domains and allow rigorous testing of specific genomic sequences on inactive X expression.
Li
Nan
N
Department of Biochemistry and Molecular Biology and Intercollege Graduate Program in Genetics, Pennsylvania State College of Medicine, Hershey, PA 17033, USA.
Carrel
Laura
L
D000818:Animals; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D053595:Embryonic Stem Cells / Q000378:metabolism; D005260:Female; D056466:Histone Demethylases; D017404:In Situ Hybridization, Fluorescence; D051379:Mice; D008822:Mice, Transgenic; D010089:Oxidoreductases, N-Demethylating; D011506:Proteins / Q000235:genetics*; D019076:Transgenes; D014960:X Chromosome / Q000235:genetics*; D049951:X Chromosome Inactivation
D011506:Proteins; D056466:Histone Demethylases; C490173:Kdm5c protein, mouse; D010089:Oxidoreductases, N-Demethylating