Segment polarity protein. Functions together with arm to transduce the Wingless (Wg) signal in embryos and in developing adult tissues. Acts as a transcriptional activator, but in the absence of arm, it binds to gro and acts as a transcriptional repressor of wg-responsive genes. Binds to the beta-catenin homolog arm or to gro. Flies exhibit a segment polarity phenotype and altered expression of the wg target genes en and Ubx. Belongs to the TCF/LEF family.