Roundabout, Axon Guidance Receptor, Homolog 4 (ROBO4)

ROBO4 has only 3 immunoglobulin and 2 fibronectin domains in its extracellular domain. ROBO4 also contains an N-terminal signal peptide, 4 putative N-glycosylation sites within the extracellular domain, a transmembrane region, and a proline-rich region within its intracellular domain. PCR detected ROBO4 in cDNA libraries from heart, adult and fetal brain, liver, lung, kidney, muscle, placenta, and small intestine, but not in those from peripheral blood leukocytes, spleen, and testis. Highest expression was in the placenta library. RT-PCR and ribonuclease protection analysis detected ROBO4 expression in endothelial cells, but not in fibroblasts, carcinoma, and neuronal cells. In situ hybridization and immunolocalization revealed ROBO4 mRNA and protein expressed in the endothelium of several tumors and placenta.