Basolateral Localization of the Caenorhabditis elegansEpidermal Growth Factor Receptor in Epithelial Cells by the PDZ Protein LIN-10

In Caenorhabditis elegans, the EGF receptor (encoded by let-23) is localized to the basolateral membrane domain of the epithelial vulval precursor cells, where it acts through a conserved Ras/MAP kinase signaling pathway to induce vulval differentiation. lin-10acts in LET-23 receptor tyrosine kinase basolateral localization, because lin-10mutations result in mislocalization of LET-23 to the apical membrane domain and cause a signaling defective (vulvaless) phenotype. We demonstrate that the previous molecular identification oflin-10was incorrect, and we identify a new gene corresponding to the lin-10genetic locus.lin-10encodes a protein with regions of similarity to mammalian X11/mint proteins, containing a phosphotyrosine-binding and two PDZ domains. A nonsense lin-10allele that truncates both PDZ domains only partially reduces lin-10gene activity, suggesting that these protein interaction domains are not essential for LIN-10 function in vulval induction. Immunocytochemical experiments show that LIN-10 is expressed in vulval epithelial cells and in neurons. LIN-10 is present at low levels in the cytoplasm and at the plasma membrane and at high levels at or near the Golgi. LIN-10 may function in secretion of LET-23 to the basolateral membrane domain, or it may be involved in tethering LET-23 at the basolateral plasma membrane once it is secreted.