Myosin Va and Endoplasmic Reticulum Calcium Channel Complex Regulates Membrane Export during Axon Guidance

During axon guidance, growth cones navigate toward attractive cues by inserting new membrane on the cue side. This process depends on Ca(2+) release from endoplasmic reticulum (ER) Ca(2+) channels, but the Ca(2+) sensor and effector governing this asymmetric vesicle export remain unknown. We identified a protein complex that controls asymmetric ER Ca(2+)-dependent membrane vesicle export. The Ca(2+)-dependent motor protein myosin Va (MyoVa) tethers membrane vesicles to the ER via a common binding site on the two major ER Ca(2+) channels, inositol 1,4,5-trisphosphate and ryanodine receptors. In response to attractive cues, micromolar Ca(2+) from ER channels triggers MyoVa-channel dissociation and the movement of freed vesicles to the cue side, enabling growth cone turning. MyoVa-Ca(2+) channel interactions are required for proper long-range axon growth in developing spinal cord in vivo. These findings reveal a peri-ER membrane export pathway for Ca(2+)-dependent attraction in axon guidance.