BCL9 and neoplasm: In the co-submitted article, Mieszczanek et al. recapitulate the increase in proximal intestinal tumour initiation following Bcl9/9l deletion in the SI of ApcMin/+ mice—an allele which lacks β-catenin binding activity42, while demonstrating that deletion almost completely blocks tumour formation in Apc1322T/+ mice—an allele which retains some β-catenin binding activity.