CHE-14, a protein with a sterol-sensing domain, is required for apical sorting in C-elegans ectodermal epithelial cells

Background: Polarised trafficking of proteins is critical for normal expres sion of the epithelial phenotype, but its genetic control is not understood . The regulatory gene lin-26 is essential for normal epithelial differentia tion in the nematode Caenorhabditis elegans. To identify potential effecter s of lin-26, we characterised mutations that result in lin-26-like phenotyp es. Here, we report the phenotypic and molecular analysis of one such mutan t line, che-14. Results: Mutations in che-14 resulted in several partially penetrant phenot ypes affecting the function of most epithelial or epithelial-like cells of the ectoderm, including the hypodermis, excretory canal, vulva, rectum and several support cells. The defects were generally linked to the accumulatio n of vesicles or amorphous material near the apical surface, suggesting tha t secretion was defective. The CHE-14 protein showed similarity to proteins containing sterol-sensing domains, including Dispatched, Patched and NPC1. A fusion protein between full-length CHE-14 and the green fluorescent prot ein became localised to the apical surface of epithelial cells that require che-14 function. Deletions that removed the predicted transmembrane domain s or extracellular loops of CHE-14 abolished apical localisation and functi on of the protein. Conclusions: We propose that CHE-14 is involved in a novel secretory pathwa y dedicated to the exocytosis of lipid-modified proteins at the apical surf ace of certain epithelial cells. Our data raise the possibility that the pr imordial function of proteins containing a sterol-sensing domain is to cont rol vesicle trafficking: CHE-14 and Dispatched in exocytosis, Patched and N PC1 in endocytosis.