The long-term objective of the proposed research is to understand the molecular and cellular events that give rise to the senses of touch and vibration. These and other mechanical senses are critical for standing and walking as well as the control of bladder function and blood pressure. Mechanotransduction is the first step in each of these senses, but remains poorly understood. It is widely believed to rely on ion channels (so-called mechano-eletrical transduction or MeT channels) that open in response to the mechanical energy carried in a touch. The proteins that form MeT channels in mammals remain unknown. Recently, we demonstrated that MEC-4 and MEC-10 are pore-forming subunits of the MeT channel responsible for sensitivity to low-intensity touch in C. elegans (O'Hagan et al, 2005, Nat Neurosci 8: 43.). Now that the molecular identity of the MeT channel in C. elegans touch receptor neurons is known, we seek answers to the key questions of 1) how force is transferred from the body surface to MeT channels and 2) how such forces lead to channel opening. We are particularly interested in understanding how touch receptor neurons detect forces as small as 100nm, are tuned to respond primarily to changes in force (vibration) and respond to stimulation in less than 1 millisecond.
Three aims are proposed. First, we will determine whether or not membrane deformation is sufficient to activate recombinant C. elegans MeT channels (Aim 1) and explore the possibility that such sensitivity, if present, might rely on a conserved sequence motif present in the 2nd transmembrane domain of MEC-4 and MEC-10 (Aim 2). Next, we will determine if in vivo activation of MeT channels involves visco-elastic elements that could act as energy storage devices during compression (Aim 3). Finally, we will investigate the role of microtubules and the microtubule bundle in force transfer and amplification (Aim 4A), pairing in vivo electrical recording with ultrastructural analysis of the microtubule bundle and investigate the contribution of microtubule- and actin- binding proteins to force transfer. We also propose to develop and deploy new devices for controlled application of mechanical stimuli (both force and displacement) and for measuring forces generated by freely moving C. elegans worms. The proposed research combines our unique expertise in sensory biophysics, in vivo electrical recording from identified C. elegans neurons, genetic analysis, and ultrastructural studies to derive a profound understanding of the sense of touch. What is learned from these studies has the potential to improve understanding of touch sensation and dysfunction in disease and normal aging.
The senses of touch and vibration are compromised in normal aging and by chronic diseases such as diabetes. Recent estimates suggest that the health costs due to diabetes- and age-related dysfunction of touch and vibration sensation are more than $28 billion annually. This proposal seeks to improve understanding of touch sensation by studying the roundworm C. elegans, a simple animal whose sense of touch is better studied than our own. What is learned from this research has the potential to provide new insight into possible diagnostic tools and treatments for the degradation of touch sensation.
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