Induces expression of a number of neural crest marker genes as part of a heterodimer with isoform b of pbx1, to specify neural crest cell fate. Binds to a highly conserved region in the promoter of the neural crest marker gene zic3. Interacts with pbx1 isoform b. Relocation from the cytoplasm to the nucleus is dependent on interaction with pbx1 isoform b. Additional isoforms seem to exist. In the embryo, displays a broad expression pattern with high levels observed in tissues of neural cell fate such as midbrain, hindbrain, dorsal portion of the neural tube, and neural crest-derived branchial arches. Widely expressed in the adult with highest levels in brain and spleen. Levels of isoform 1 decrease slightly during gastrulation but show a marked increase during neurulation and throughout embryogenesis. Expression of isoform 2 is low during early embryogenesis but increases after tailbud stages. Belongs to the TALE/MEIS homeobox family.