ELK-L3, A NOVEL TRANSMEMBRANE LIGAND FOR THE EPH FAMILY OF RECEPTOR TYROSINE KINASES, EXPRESSED IN EMBRYONIC FLOOR PLATE, ROOF PLATE AND HINDBRAIN SEGMENTS

The Eph family of receptor tyrosine kinases has 13 distinct members an d seven ligands for these receptors have been described to date, These receptors and their ligands have been implicated in regulating neuron al axon guidance and in patterning of the developing nervous system an d may also serve a patterning and compartmentalization role outside of the nervous system as well, The ligands are all membrane-attached, an d this attachment appears to be crucial for their normal function; fiv e of the known ligands are linked to the membrane,ia a glycosyl phosph otidylinositol (GPI) linkage, while tate of the ligands are transmembr ane proteins, Despite the large number of Eph family receptors and lig ands, they can be divided into just two major subclasses based on thei r binding specificities. All the GPI-anchored ligands bind and activat e one subclass of the Eph receptors (that represented by Eck) while th e two transmembrane ligands bind and activate the other major subclass of receptors (represented by Elk), Here we report the identification and characterization of the third, and most divergent, member of the t ransmembrane group of Eph ligands, which we term Elk-L3 (ElK-related r eceptor ligand number 3), Elk-L3 is notable for its remarkably restric ted and prominent expression in the Boor plate and roof plate of the d eveloping neural tube and its rhombomere-specific expression in the de veloping hindbrain, The Elk-L3 gene has been localized to mouse chromo some 11 and human chromosome 17.