IMMUNOLOCALIZATION OF THE NUK RECEPTOR TYROSINE KINASE SUGGESTS ROLESIN SEGMENTAL PATTERNING OF THE BRAIN AND AXONOGENESIS

Neural kinase (Nuk) encodes a murine receptor-like tyrosine kinase bel onging to the Eph/Elk/Eck family. Protein localization studies indicat e that during early embryogenesis Nuk is confined to the developing ne rvous system, where it marks segments along the axis of the neural tub e in the hindbrain (rhombomeres r2, r3 and r5) and specific morphologi cal bulges of the midbrain and forebrain. Subcellular localization of Nuk indicates that this receptor is concentrated at sites of cell-cell contact, often involving migrating neuronal cells or their extensions . Most notably, high levels of Nuk protein are found within initial ax on outgrowths and associated nerve fibers. The axonal localization of Nuk is transient and is not detected after migrations have ceased, sug gesting a role for this tyrosine kinase during the early pathfinding a nd/or fasciculation stages of axonogenesis. The subcellular localizati on of Nuk, as well as the presence of fibronectin type III and immunog lobulin-like adhesive domains on the extracellular region, suggest thi s receptor tyrosine kinase may function to regulate specific cell-cell interactions during early development of the murine nervous system.