The response to gentle body touch in C. elegans is mediated by a set of six mechanosensory neurons. On the basis of genetic interactions, electrophysiology, and molecular studies of the mec genes and their products, we have proposed that a mechanosensory complex converts mechanical stimuli into electrical signals. Two degenerins, MEC-4 and MEC-10, which produce amiloride-senstive ionic currents in Xenopus oocytes, are believed to conduct the mechanosensitive currents in vivo. MEC-2, which interacts and regulates the MEC-4/10 channels in oocytes, forms a complex with them. Whole-mount immunohistochemistry using rabbit polyclonal antibodies against MEC-2 reveals that MEC-2 is localized to regular puncta along the entire length of the touch cell processes. Indirect immunofluorescence of MEC-2 is colocalized with full-length MEC-4::GFP, also suggesting that MEC-2 and the degenerins form a complex. To study further the punctate pattern of MEC-2, we stained different mec mutants with the MEC-2 antibodies. Normally touch cells are distinguished by their bundle of 15-protofilament microtubules and their prominent extracellular matrix.
mec-7 and
mec-12, which encode beta- and alpha-tubulins, respectively, are required for these microtubules;
mec-1 is needed for the extracellular matrix. The axonal distribution of MEC-2 is almost completely abolished in
mec-7 and
mec-12 mutants. Cell body staining of MEC-2, however, is noticeably elevated. Therefore, the touch cell-specific microtubules are involved in the axonal distribution of MEC-2. In contrast, the
mec-1-dependent extracellular matrix is not required to localize MEC-2, since the MEC-2 punctate pattern is unchanged in
mec-1 mutants. MEC-4, MEC-10 and MEC-6, as well as MEC-2, are essential components of the mechanosensory channel complex. MEC-2 staining becomes diffuse in
mec-4,
mec-10 and
mec-6 mutants, suggesting that the integrity of the channel complex is important for the localization of MEC-2. MEC-4::GFP expression, however, remains punctate in
mec-2 animals. Therefore, MEC-2 is not required for the localization of mechanosensory complexes. MEC-2 interacts with the cytoplasmic N-terminus of MEC-4 in GST pull-down experiments. By deleting various regions, we find that the stomatin-like region of MEC-2 is needed for this binding. MEC-2 antibody staining becomes diffuse in alleles that have missense mutations in stomatin-like region but remains punctate in alleles that have missense mutations outside this region. Therefore, the stomatin-like region is required for MEC-2 to interact with the mechanosensory channel complexes in vivo.