FIGURE 22-32 The MEC-4 touch-receptor complex in C. elegans. Mutations in any of the MEC genes can reduce or inactivate normal responses of the worm to a gentle body touch. The MEC-4 and MEC-10 proteins are the pore-forming subunits of the Na⁺ channel; MEC-2 and MEC-6 are accessory subunits that enable channel activity. Mechanotransduction also requires a specialized extracellular matrix, consisting of MEC-5, a collagen isoform, and MEC-1 and MEC-9, both proteins with multiple EGF repeats. MEC-7 and MEC-12 are tubulin monomers that form novel 15-protofilament microtubules that are somehow also required for touch sensitivity. See E. Lumpkin, K. Marshall, and A. Nelson, 2010, J. Cell Biol. 191:237.