A direct interaction between IP3 receptors and myosin II regulates IP3 signaling in C-elegans

Molecular and physiological studies of cells implicate interactions between the cytoskeleton and the intracellular calcium signalling machinery as an important mechanism for the regulation of calcium signalling [1-11]. However, little is known about the functions of such mechanisms in animals. A key component of the calcium signalling network is the intracellular release of calcium in response to the production of the second messenger inositol 1,4,5-trisphosphate (IP3), mediated by the IP3 receptor (IP3R) [12-14]. We show that C. elegans IP(3)Rs, encoded by the gene itr-1, interact directly with myosin II. The interactions between two myosin proteins, UNC-54 and MYO-1, and ITR-1 were identified in a yeast two-hybrid screen and subsequently confirmed in vivo and in vitro. We defined the interaction sites on both the IP3R and MYO-1. To test the effect of disrupting the interaction in vivo we over-expressed interacting fragments of both proteins in C. elegans. This decreased the animal's ability to upregulate pharyngeal pumping in response to food. This is a known IP3-mediated process [15]. Other IP3-mediated processes, e.g., defecation [16], were unaffected. Thus it appears that interactions between IP(3)Rs and myosin are required for maintaining the specificity of IP3 signalling in C. elegans and probably more generally.