| In C. 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. The gene lin-10 acts in LET-23 RTK basolateral localization, as lin-10 mutations result in mislocalization of LET-23 to the apical membrane domain and cause a signaling defective (vulvaless) phenotype. This result places lin-10 in a class of genes, including lin-2 and lin-7, that encode important trans-acting factors in basolateral LET-23 localization. lin-10 encodes a protein with regions of similarity to mammalian X11/mint proteins, containing a phosphotyrosine-binding and two PDZ domains. Immunocytochemical experiments show that LIN-10 is expressed in epithelial cells and in neurons. LIN-10 is present at low levels in the cytoplasm and at the plasma membrane and high levels at or near the Golgi, suggesting a possible role in secretion of LET-23 to the basolateral membrane domain or tethering LET-23 at the basolateral membrane. Genetic screens to identify additional genes that act in LET-23 localization are described. Additionally, LET-23 localization is extensively characterized in a second cell type, the intestinal epithelia. LET-23 is localized to the basolateral and lateral membrane in embryonic and larval intestinal epithelia, respectively. This localization is dependent on LIN-2, LIN-7 and LIN-10. Additional mechanisms also may act in parallel with the LIN-2/LIN-7/LIN-10 complex in larva. Lastly, reverse genetics using dsRNA mediated gene interference is shown to be effective in intestinal epithelia, and a function for the C. elegans homolog of Dlg in cell polarity is demonstrated. |
