Differences in binding preferences for XIST partners are observed in mammals with different early pregnancy morphologies

In comparison to protein-coding genes, long non-coding RNAs (lncRNAs) are poorly conserved between species at the sequence level yet they often perform conserved and essential regulatory roles. The lncRNA XIST mediates X chromosome inactivation (XCI) through the interaction of numerous proteins, most of which bind to its repeat regions. Whilst XIST is present across placental mammals, its sequence is divergent. In addition, the timing and mechanistic details of the process of XCI also vary across placental mammals. Here, we sought to determine whether XIST interactor proteins previously identified in a model mammalian species (mouse) also bind in other mammals which exhibit divergent timing of XCI (human and bovine) and differing pre-implantation embryo morphology. We show that XIST and its putative protein partners are coordinately expressed in the endometria of mammals with different pre-implantation embryo morphologies. RNA immunoprecipitations revealed that human WTAP, SPEN, hnRNPK and CIZ1 proteins bind human XIST. CIZ1-XIST binding was also detected in bovine. In both human and cow, we found CIZ1 binds to the repeat E element of XIST. However, human CIZ1 protein is not able to bind bovine repeat E, indicating a species-specific binding interaction. Together these data indicate that several of the key RNA-protein interactions with XIST are common across placental mammals, even though we observe divergence in both the RNA sequence of XIST, and early embryo morphologies. This work sheds light upon the evolution of RNA-protein binding interactions, revealing that the binding events can be conserved even when the precise mechanism of binding has changed. Statements and DeclarationsAuthors have no financial or non-financial interests that are directly or indirectly related to the work submitted for publication.