Roundabout homolog 4(ROBO4) contains 2 fibronectin type-III domains, 2 Ig-like C2-type (immunoglobulin-like) domains and belongs to the immunoglobulin superfamily.The protein is a receptor for slit proteins, at least for SLIT2, and seems to be involved in angiogenesis and vascular patterning. ROBO4 may mediate the inhibition of primary endothelial cell migration by Slit proteins.