Required for locomotion and mechanical sensing in proprioceptive neurons by transducing dendrite stretching into cellular responses. Required for transduction of mechanical stimuli in a specific subpopulation of proprioceptive neurons that sense joint angles. Probably does not constitute the mechanically activated channel and may rather serve as an accessory module required for the proper localization or function of the transduction channels. Specifically localizes to the distal part of the sensory dendrite. Does not accumulate in any other part of the cell. Expressed in limited populations of proprioceptive neurons that sense a mechanical property of specific joints. In the legs, localizes to 3 labeled neurons: one at the femur-tibia joint, the second at the tibia-tarsus joint, and the third spanning the second tarsal segment. Dendrites of stum-expressing neurons in legs are stretched by both flexion and extension of corresponding joints. Impaired walking characterized by walking uncoordination and reduced climbing speed. Type I neurons are apparently unaffected. Abolition of responses to stretching: although the dendritic stretching is not significantly affected, the Ca(2+) responses to both acute and obtuse joint angles are abolished in the mutant. Axons and cell bodies are indistinguishable from controls, while the sensory dendrite exhibit abnormalities: in some of the stum-expressing neurons the tip of the dendrite is overgrown and extended into the distal segment of the joint. Expression of the mouse ortholog (AC Q0VBF8) in mutant flies rescues the phenotype. Was named stumble because of the walking impairment phenotype. Belongs to the SPEC3 family. Stum subfamily.