X-chromosome inactivation in XX androgenetic mouse embryos surviving implantation.
Using genetic and cytogenetic markers, we assessed early development and X-chromosome inactivation (X-inactivation) in XX mouse androgenones produced by pronuclear transfer. Contrary to the current view, XX androgenones are capable of surviving to embryonic day 7.5, achieving basically random X-inactivation in all tissues including those derived from the trophectoderm and primitive endoderm that are characterized by paternal X-activation in fertilized embryos. This finding supports the hypothesis that in fertilized female embryos, the maternal X chromosome remains active until the blastocyst stage because of a rigid imprint that prevents inactivation, whereas the paternal X chromosome is preferentially inactivated in extra-embryonic tissues owing to lack of such imprint. In spite of random X-inactivation in XX androgenones, FISH analyses revealed expression of stable Xist RNA from every X chromosome in XX and XY androgenonetic embryos from the four-cell to morula stage. Although the occurrence of inappropriate X-inactivation was further suggested by the finding that Xist continues ectopic expression in a proportion of cells from XX and XY androgenones at the blastocyst and the early egg cylinder stage, a replication banding study failed to provide positive evidence for inappropriate X-inactivation at E6. 5.
Okamoto
I
I
Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 0600810, Japan.
Tan
S
S
Takagi
N
N
D000818:Animals; D004303:Dosage Compensation, Genetic; D047108:Embryonic Development; D005260:Female; D018392:Genomic Imprinting; D008297:Male; D051379:Mice; D009030:Mosaicism; D053652:Nuclear Transfer Techniques; D011247:Pregnancy; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000302:isolation & purification; D012729:Sex Chromosome Aberrations; D012733:Sex Differentiation; D014157:Transcription Factors / Q000302:isolation & purification; D014960:X Chromosome
D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D014157:Transcription Factors; C077885:XIST non-coding RNA