X chromosome choice occurs independently of asynchronous replication timing.
In mammals, dosage compensation is achieved by X chromosome inactivation in female cells. Xist is required and sufficient for X inactivation, and Xist gene deletions result in completely skewed X inactivation. In this work, we analyzed skewing of X inactivation in mice with an Xist deletion encompassing sequence 5 KB upstream of the promoter through exon 3. We found that this mutation results in primary nonrandom X inactivation in which the wild-type X chromosome is always chosen for inactivation. To understand the molecular mechanisms that affect choice, we analyzed the role of replication timing in X inactivation choice. We found that the two Xist alleles and all regions tested on the X chromosome replicate asynchronously before the start of X inactivation. However, analysis of replication timing in cell lines with skewed X inactivation showed no preference for one of the two Xist alleles to replicate early in S-phase before the onset of X inactivation, indicating that asynchronous replication timing does not play a role in skewing of X inactivation.
Gribnau
Joost
J
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Luikenhuis
Sandra
S
Hochedlinger
Konrad
K
Monkhorst
Kim
K
Jaenisch
Rudolf
R
D000483:Alleles; D000818:Animals; D002460:Cell Line; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics; D042522:DNA Replication Timing / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D004303:Dosage Compensation, Genetic; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D047108:Embryonic Development / Q000235:genetics; D005091:Exons / Q000235:genetics; D005260:Female; D005434:Flow Cytometry; D017353:Gene Deletion; D005838:Genotype; D049452:Green Fluorescent Proteins / Q000235:genetics; D056466:Histone Demethylases; D017404:In Situ Hybridization, Fluorescence; D053592:Interleukin-1 Receptor-Associated Kinases; D008297:Male; D051783:Methyl-CpG-Binding Protein 2; D051379:Mice; D008822:Mice, Transgenic; D010089:Oxidoreductases, N-Demethylating; D011494:Protein Kinases / Q000235:genetics; D011506:Proteins / Q000235:genetics; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics; D016196:S Phase / Q000235:genetics; D013234:Stem Cells / Q000502:physiology; D014960:X Chromosome / Q000235:genetics*
D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C497393:Mecp2 protein, mouse; D051783:Methyl-CpG-Binding Protein 2; D011506:Proteins; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D012097:Repressor Proteins; C077885:XIST non-coding RNA; D049452:Green Fluorescent Proteins; D056466:Histone Demethylases; C490173:Kdm5c protein, mouse; D010089:Oxidoreductases, N-Demethylating; D011494:Protein Kinases; D053592:Interleukin-1 Receptor-Associated Kinases