News Finding: They then found that the loss of SMCHD1 prevented the spreading of Xist across the chromosome and kept the two large domains, which the team named S1 and S2 compartments, from being merged into the typical compartment-less inactive X structure.
Paper Finding: Such a stepwise mechanism is consistent with how Xist RNA spreads.
News Context: The team's experiments in mouse cells first confirmed that the presence of SMCHD1 was necessary for the silencing of a large subset of genes on the inactive X chromosome. They then found that the loss of SMCHD1 prevented the spreading of Xist across the chromosome and kept the two large domains, which the team named S1 and S2 compartments, from being merged into the typical compartment-less inactive X structure. By bridging the S1 and S2 compartments, SMCHD1 was found to induce their merging into the conformation that prevents gene expression.
Paper Context: When SMCHD1 is recruited at a later stage , S1/S2 compartments are merged together to create a ''compartment-less'' structure (Figures 4 and 7). Such a stepwise mechanism is consistent with how Xist RNA spreads. In this way, Xist could co-segregate with gene-rich regions located in other A compartments.