A proximal conserved repeat in the Xist gene is essential as a genomic element for X-inactivation in mouse.
X-inactivation in female mammals is triggered by the association of non-coding Xist RNA in cis with the X chromosome. Although it has been suggested that the A-repeat located in the proximal part of the Xist RNA is required for chromosomal silencing in ES cells, its role in mouse has not yet been addressed. Here, we deleted the A-repeat in mouse and studied its effects on X-inactivation during embryogenesis. The deletion, when paternally transmitted, caused a failure of imprinted X-inactivation in the extraembryonic tissues, demonstrating the essential role of the A-repeat in X-inactivation in the mouse embryo. Unexpectedly, the failure of X-inactivation was caused by a lack of Xist RNA rather than by a defect in the silencing function of the mutated RNA, which we expected to be expressed from the mutated X. Interestingly, the normally silent paternal copy of Tsix, which is an antisense negative regulator of Xist, was ectopically activated in the preimplantation embryo. Furthermore, CpG sites in the promoter region of paternal Xist, which are essentially unmethylated in the extraembryonic tissues of the wild-type female embryo, acquire a significant level of methylation on the mutated paternal X. These findings demonstrate that the DNA sequence deleted on the mutated X, most probably the A-repeat, is essential as a genomic element for the appropriate transcriptional regulation of the Xist/Tsix loci and subsequent X-inactivation in the mouse embryo.
Hoki
Yuko
Y
Division of Human Genetics, National Institute of Genetics, Research Organization of Information and Systems, 1111 Yata, Mishima 411-8540, Japan.
Kimura
Naomi
N
Kanbayashi
Minako
M
Amakawa
Yuko
Y
Ohhata
Tatsuya
T
Sasaki
Hiroyuki
H
Sado
Takashi
T
D000483:Alleles; D000818:Animals; D001755:Blastocyst / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation; D017124:Conserved Sequence; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D020964:Embryo Loss; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism; D005321:Extraembryonic Membranes / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D016678:Genome / Q000235:genetics*; D040582:Inheritance Patterns / Q000235:genetics; D008297:Male; D051379:Mice; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics* / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D017384:Sequence Deletion; D013094:Spermatozoa / Q000378:metabolism; D014158:Transcription, Genetic; D014960:X Chromosome / Q000235:genetics; D049951:X Chromosome Inactivation / Q000235:genetics*
D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C465658:Tsix transcript, mouse; C077885:XIST non-coding RNA