Enables beta-catenin binding activity. Acts upstream of or within several processes, including canonical Wnt signaling pathway; skeletal muscle cell differentiation; and somatic stem cell population maintenance. Located in nucleus. Is expressed in several structures, including respiratory system cartilage; sensory organ; skeleton; trunk unsegmented mesenchyme; and vibrissa. Orthologous to human BCL9L (BCL9 like). [provided by Alliance of Genome Resources, Apr 2022]