Ectopically expressed Airn lncRNA deposits Polycomb with a potency that rivals Xist

We report that when expressed at similar levels from an isogenic locus, the Airn lncRNA induces Polycomb deposition with a potency that rivals Xist. However, when subject to the same degree of promoter activation, Xist is more abundant and more potent than Airn. Our data definitively demonstrate that the Airn lncRNA is functional and suggest that Xist achieved extreme potency in part by evolving mechanisms to promote its own abundance.