In animals, locomotion is mediated by highly coordinated sensorimotor feedback system. C. elegans generates sinusoidal locomotion via periodic bending of its head and body. The SMD motor neurons, that innervate to head muscles and project posterior processes to the tail, have been proposed to sense the muscle stretch and regulate head locomotion (White et al., 1986; Hendricks et al., 2012; Shen et al., 2016). However, the molecular mechanisms by which SMD mediates proprioceptive signals to modulate locomotion are still unclear. To identify factors that regulate SMD-mediated head bending, we performed candidate gene search and found that TRPC channels,
trp-1 and
trp-2, are co-expressed in SMD (Feng et al., 2006). Since we did not observed altered locomotion defects in single mutants of either
trp-1 or
trp-2, we generated
trp-1 trp-2 double mutants and found that these animals exhibit ventral-directed circles during forward movement; we name this phenotype as ventral circling. Expression of either TRP-1 or TRP-2 by using a SMDD specific promoter rescued ventral circling phenotype of
trp-1 trp-2 mutants, and SMDD ablated worms also exhibited ventral circling. These results indicate that the ventral circling phenotype of
trp-1 trp-2 mutants is due to the functional defects of SMDD. Ca2+ activity of SMD is correlated with head bending direction in wild-type animals, whereas Ca2+ activity SMDD but not SMDV is not correlated with head bending in
trp-1 trp-2 mutants. These impaired correlation Ca2+ dynamic of SMDD with head bending in
trp-1 trp-2 double mutants was restored by expressing
trp-1 cDNA using the SMDD specific promoter. Furthermore, ectopic expression of the known stretch receptors, C. elegans
trp-4 or Drosophila TRP? in SMDD were sufficient to rescue ventral circling locomotion of
trp-1 trp-2 double mutants. Currently, we are investigating whether activations of TRP-1 or TRP-2 are induced by membrane stretch using electrophysiology in heterologous systems. Taken together, we propose that
trp-1 and
trp-2 act as proprioceptive receptors in the SMD motor neurons to sense the dorsal head movement and correlate SMDD motor neuronal activity with head bending.