Integrated kinetics of X chromosome inactivation in differentiating embryonic stem cells.
Inactivation of the X chromosome during early female development and the subsequent maintenance of this transcriptionally inert state through countless cell divisions remain a paradigm for epigenetic regulation in mammals. Nevertheless, the exact mechanisms underlying this chromosome-wide silencing process remain unclear. Using differentiating female embryonic stem (ES) cells as a model system, we recently found that histone H3 tail modifications are among the earliest known chromatin changes in the X inactivation process, appearing as soon as Xist RNA accumulates on the X chromosome, but prior to transcriptional silencing of X-linked genes (Heard et al., 2001). In this report we present an integrated analysis of the sequence of early events and chromatin modifications underlying X inactivation in differentiating female ES cells. We have extended our previous analysis concerning changes in histone tail modification states. We find that the hypomethylation of Arg-17 and that of Lys-36 on histone H3 also characterize the inactive X chromosome, and that these profiles show a similarly early onset during the initiation of X inactivation. In addition, we have investigated the kinetics of the shift in replication timing of the X chromosome undergoing inactivation. This event occurs slightly later than Xist RNA coating and the chromatin modifications. Finally, from an early stage in the X inactivation process, characteristic histone modification patterns can be found on the X chromosome at mitosis, suggesting that they represent true epigenetic marks of the inactive state.
Chaumeil
J
J
Mammalian Developmental Epigenetics Group, CNRS UMR 218, Curie Institute, Paris, France.
Okamoto
I
I
Guggiari
M
M
Heard
E
E
D000107:Acetylation; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D004303:Dosage Compensation, Genetic; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism*; D005260:Female; D006657:Histones / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D007399:Interphase / Q000235:genetics; D007700:Kinetics; D051379:Mice; D008938:Mitosis / Q000235:genetics; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors; D014960:X Chromosome / Q000235:genetics* / Q000378:metabolism
D006657:Histones; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C077885:XIST non-coding RNA