Receptor for Slit proteins, at least for SLIT2, and seems to be involved in angiogenesis and vascular patterning. May mediate the inhibition of primary endothelial cell migration by Slit proteins. Involved in the maintenance of endothelial barrier organization and function (By similarity). Interacts with SLIT2 and ENAH. Expressed specifically in embryo and adult vascular endothelium. In embryonic development of vascular endothelium, it shows a dynamic expression pattern within vessels, with expression starting in the larger axial vessels and intersomitic vessels at earlier ages, and changing to intersomitic vessel and capillary expression at later stages. At 9.0 dpc, is expressed in the central vessels, the dorsal aorta, and intersomitic vessels. At 9.5 dpc, is highly expressed in intersomitic vessels with little expression remaining in dorsal aortae. By 10.0 dpc, is detected in capillary vessels, the capillary plexus of the limb buds, and throughout the endothelium as microvessels sprout from the dorsal aortae. No expression was detected in the neural tube at 9.0 dpc and 9.5 dpc. However, it is detected within the capillaries sprouting into the neural tube, as well as in the adjacent perineural capillary plexus at 10.0 dpc. At 11.5 dpc, it is expressed in the endocardial layer of the cushions and delamination zones. By 17 dpc, it is detected in both the endothelial and interstitial cells of the developing aortic valve and endothelial cells of the proximal aorta. At 5 weeks after birth, it is localized to the endothelial layer of the ascending aorta and persists throughout postnatal development (PubMed:30455415). Homozygous knockout mice exhibit a complex cardiovascular phenotype that includes a combination of aortic valve thickening with or without bicuspid aortic valve, aortic valve stenosis, regurgitation and/or ascending aortic aneurysm. In general, these phenotypes are observed with low penetrance and male predominance. Belongs to the immunoglobulin superfamily. ROBO family. Extended N-terminus. Truncated N-terminus. Extended N-terminus.