The many roles of PTK7: A versatile regulator of cell–cell communication

PTK7 (protein tyrosine kinase 7) is an evolutionarily conserved transmembrane receptor with functions in various processes ranging from embryonic morphogenesis to epidermal wound repair. Here, we review recent findings indicating that PTK7 is a versatile co-receptor that functions as a molecular switch in Wnt, Semaphorin/Plexin and VEGF signaling pathways. We focus in particular on the role of PTK7 in Wnt signaling, as recent data indicate that PTK7 acts as a Wnt co-receptor, which activates the planar cell polarity pathway, but inhibits canonical Wnt signaling.