The Multipurpose 15-Protofilament Microtubules in C. elegans Have Specific Roles in Mechanosensation

Because microtubules perform many essential functions in neurons, delineating unique roles attributable to these organelles presents a formidable challenge. Microtubules endow neurons with shape and structure and are required for developmental processes including neurite outgrowth [1], intracellular transport [2], and synapse formation and plasticity [3, 4]; microtubules in sensory neurons may be required for the above processes in addition to a specific sensory function. In Caenorhabditis elegans, six touch receptor neurons (TRNs) sense gentle touch [5] and uniquely contain 15-protofilament microtubules [6]. Disruption of these microtubules by loss of either the MEC-7 beta-tubulin [7] or MEC-12 alpha-tubulin [8) or by growth in 1 mM colchicine causes touch insensitivity [5, 6], altered distribution of the touch transduction channel, and a general reduction in protein levels. We show that the effect on touch sensitivity can be separated from the others; microtubule depolymerization in mature TRNs causes touch insensitivity but does not result in protein distribution and production defects. In addition, the mec-12(61605) mutation selectively causes touch insensitivity without affecting microtubule formation and other cellular processes. Touching e1605 animals produces a reduced mechanoreceptor current that inactivates more rapidly than in wild-type, suggesting a specific role of the microtubules in mechanotransduction.