Axl (Ufo, Ark), Dtk (Sky, Tyro3, Rse, Brt) and Mer (human and mouse orthologs of chicken c-Eyk) constitute the TAM receptor tyrosine kinase subfamily. This RTK subfamily is characterized by an extracellular domain that consists of two Ig-like motifs and two fibronectin type III motifs. These receptors bind the vitamin K-dependent protein Growth Arrest Specific Gene 6 (Gas6). Receptor activation leads to cell proliferation, migration, or the prevention of apoptosis. Cellular signaling through this family of RTKs is involved in hematopoiesis, embryonic development, tumorigenesis, and spermatogenesis.