Mer

Axl (Ufo, Ark), Dtk (Sky, Tyro3, Rse, Brt) and Mer (human and mouse homologues of chicken c-Eyk) constitute a receptor tyrosine kinase subfamily. The extracellular domains of these proteins contain two Ig-like motifs and two fibronectin type III motifs. This characteristic topology is also found in neural cell adhesion molecules and in receptor tyrosine phosphatases. These receptors bind the vitamin K-dependent protein growth-arrest-specific gene 6 (Gas6) which is structurally related to the anti-coagulation factor protein S. Binding of Gas6 induces receptor autophosphorylation and downstream signaling pathways that can lead to cell proliferation, migration or the prevention of apoptosis. Recent studies suggest that this family of tyrosine kinase receptors may be involved in hematopoiesis, embryonic development, tumorigenesis and regulation of testicular functions.