Vital for larval development (PubMed:1339334). During salivary tube elongation, possibly modulates cellular adhesion between the apical surface and apical extracellular matrix, and acts as an apical membrane determinant that functions in apical membrane expansion independently of crb and Cad99C (PubMed:24718992). Expressed in most, if not all, ectodermal tissues which produce a cuticle. Throughout development. The extracellular domain is sufficent for conferring apical characteristics on the salivary gland membrane.