Acts in a planar cell polarity (PCP) complex; polarization along the apical/basal axis of epithelial cells. Regulates the polarized assembly of fibronectrin on the surface of the mesoderm during gastrulation. Essential for gastrulation cell movements, cooperating with dvl2/dsh to activate jnk. Acts together with tes to control axial elongation (By similarity). Interacts with dvl2/dsh and mapk8/jnk1. Belongs to the prickle / espinas / testin family.