Activity is required in presynaptic neurons, in a dose-dependent manner, for normal presynaptic development and morphology (PubMed:15707898). Plays a role in the formation of muscle connections, also called muscle arm extensions, between the body wall and the motor axons in the dorsal and ventral cord (PubMed:27123983). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Expressed in the pharynx, including the corpus, isthmus and terminal bulb. Defective extension of body wall muscle connections or arms towards the ventral nerve cord. Double knockout with madd-3 results in severe muscle arm extension defects. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.