Mapping the Signaling Network of Muscle-Specific Kinase

The neuromuscular junction (NMJ) represents the central node of communication between motor neurons, skeletal muscle and Schwann cells. Every voluntary movement such as breathing, walking, talking and eating relies on the appropriate function of the NMJ, and as such, much of our behavior, wellbeing and productivity are governed by this essential structure. Disorders affecting the neuromuscular system are a large group of diverse diseases includingmotor neurondiseases, musculardystrophies, autoimmune diseases and congenital myasthenic syndromes. NMJs form when a motor axon reaches a muscle fiber. Acetylcholine receptors become concentrated at the site of innervation and processes at the molecular and cellular level lead to the development of a mature and functional NMJ. The receptor tyrosine kinase MuSK is the key signaling molecule at the NMJ whose activity is required for the formation of a mature and functional NMJ. It is well established that MuSK kinase activity is tightly regulated to ensure proper NMJ development and that mutations that affect MuSK kinase activity are causally involved in congenital myasthenic syndromes. Signal transduction downstream of MuSK regulates acetylcholine receptor clustering but despite recent advances, signaling induced by MuSK activation is still largely unresolved. Consequently, understanding all the events of the signaling cascade(s) and their spatial-temporal organization remains a great knowledge gap. Therefore, we will perform a proteomics approach in combination with proximity labelling in muscle cells to decipher proteins within this signaling network and their temporal interactions. Further, we will use in vitro and in vivo approaches including loss-of-function and gain-of-function in muscle cells as well as in muscle fibers to establish the role of the identified proteins during MuSK signaling and NMJ formation. The proposed study tackles so far poorly understood aspects of MuSK function and will therefor provide valuable novel insights into the molecular mechanisms, which control the formation of a functional neuromuscular junction. We also expect to increase our knowledge about the molecular basis of pathology in patients carrying MuSK mutations thereby aiding to the diagnosis and treatment of congenital myasthenic syndromes.