Probable coreceptor of Wnt proteins. Involved in neuronal pathway recognition and ventral muscle attachment site selection. Non-vital for development. May be part of a signal transduction cascade involved in learning and possibly memory. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] In the embryonic abdominal hemisegment, expression is restricted to cell body, axon and growth cone of a cluster of 20 ventral nerve cord interneurons. During muscle growth and attachment events in the embryonic abdominal hemisegment, expression is in somatic muscle fibers 21-23 at 10-13 hours and 2 patches of approximately 15 neighboring epidermal cells (dorsal and ventral attachment sites) at 6-13 hours. The extracellular WIF domain is responsible for Wnt binding. Belongs to the protein kinase superfamily. Tyr protein kinase family.