BCL9 and B-cell non-Hodgkin lymphoma: This bridge protein, and its two vertebrate homologs BCL9 and BCL9L (referred to as BCL9/9L; the name derives from their causative role in B‐cell lymphoma, Willis et al., 1998), were thought to have the sole function of tethering the NPF‐containing, NHD transactivation domain of Pygo to the β‐catenin‐dependent complex.