Pluto Bioinformatics

GSE80810: Paternal X inactivation is fully Xist-dependent with strain-specific kinetics revealed by single cell embryo profiling

Bulk RNA sequencing

In Mammals, the difference in sex-chromosome constitution between males (XY) and females (XX) has led to the evolution of dosage compensation strategies, including silencing of an entire X chromosome in females. In mice, X chromosome inactivation (XCI) first occurs in the pre-implantation embryo. Here the non-coding Xist RNA is expressed only from the paternal allele and the paternal X (Xp) becomes inactivated. The Xp is reactivated in the inner cell mass and this is followed by random XCI in the embryo proper, while in extra-embryonic tissues the Xp remains inactive. Although random XCI initiation is thought to be fully Xist-dependent in the mouse, initiation of imprinted XCI was reported to be Xist-independent. Furthermore, the chromosome-wide dynamics of XCI in early embryos of reciprocal inter-specific crosses, which better reflect a natural situation, have never been investigated. Here we report that the expression dynamics of X-linked genes depends both on strain and parent of origin, as well as on X chromosome location, using single-cell RNA-sequencing (scRNAseq) of early mouse embryos. We also demonstrate that initiation of imprinted XCI absolutely requires Xist and that its absence leads to genome-wide transcriptional misregulation in the early blastocyst, with massive over-expression of specific genes such as Rhox5 and failure to activate the extra-embryonic pathway essential for early post-implantation development. This study provides important insights into the transcriptional and allelic dynamics of the X chromosome and the first evidence of dosage compensation failure as early as the blastocyst stage. SOURCE: Nicolas Servant (Nicolas.Servant@curie.fr) - Institut Curie