Functions in cell-cell adhesion, cell migration and axon guidance, exerting an attractive or repulsive role depending on its interaction partners (PubMed:19056886, PubMed:25374360). Plays a role in the spatial organization of brain neurons (PubMed:25374360). Plays a role in vascular development in the retina (PubMed:25374360). Plays a role in cell-cell adhesion via its interaction with ADGRL3 and probably also other latrophilins that are expressed at the surface of adjacent cells (PubMed:22405201, PubMed:25374360). Interaction with the intracellular domain of ROBO1 mediates axon attraction towards cells expressing NTN1 (PubMed:24560577). Mediates axon growth cone collapse and plays a repulsive role in neuron guidance via its interaction with UNC5B, and possibly also other UNC-5 family members (PubMed:21673655, PubMed:25374360). Promotes neurite outgrowth (in vitro) (By similarity). Mediates cell-cell contacts that promote an increase both in neurite number and in neurite length (By similarity). Plays a role in the regulation of the density of glutamaergic synapses (PubMed:22405201). Plays a role in fibroblast growth factor-mediated signaling cascades (PubMed:16872596). Required for normal morphogenesis during embryonic development, but not for normal embryonic patterning (PubMed:19056886). Required for normal ventral closure, headfold fusion and definitive endoderm migration during embryonic development (PubMed:18448090). Required for the formation of a normal basement membrane and the maintenance of a normal anterior visceral endoderm during embryonic development (PubMed:19056886). Monomer and homodimer (By similarity). Self-associates (via leucine-rich repeats), giving rise to homooligomers (PubMed:25374360). Interacts with FGFR1 (PubMed:16872596). Interacts (via extracellular domain) with ADGRL1/LPHN1 and LPHN2 (via olfactomedin-like domain) (PubMed:22405201). Interacts (via extracellular domain) with ADGRL3 (via olfactomedin-like domain) (PubMed:24739570, PubMed:22405201, PubMed:26235031). Interacts (via extracellular domain) with UNC5B (via Ig domain) (PubMed:19492039, PubMed:21673655, PubMed:22405201, PubMed:25374360). May also interact (via extracellular domain) with UNC5A and UNC5C (PubMed:22405201). Interacts (via extracellular domain) with UNC5D (via extracellular domain) (PubMed:19492039). Identified in complexes composed of FLRT3, ADGRL3 and UNC5B, respectively FLRT3, ADGRL3 and UNC5D (By similarity). Interacts (via cytoplasmic domain) with ROBO1 (PubMed:24560577). Detected on dendritic punctae that colocalize in part with glutamaergic synapses, but not with GABAergic synapses. Proteolytic cleavage in the juxtamembrane region gives rise to a shedded ectodomain (PubMed:21673655). Detected in adult brain (PubMed:21350012). Detected in embryonic rostral thalamus neurons (at protein level) (PubMed:24560577). Detected in embryonic rostral thalamus neurons (PubMed:24560577). Detected in neonate eye, in the inner plexiform layer and the outer nuclear layer (PubMed:25374360). Detected in embryonic brain at 13 dpc. Levels in brain decrease gradually after 15 dpc, but expression continues after birth (PubMed:21673655). Detected in embryonic myocardium, body wall and pro-epicardial organ at 9.5 dpc. Detected throughout the myocardium at 10.5 dpc, but levels in the epicardial cell layer are strongly decreased. Almost exclusively detected in the neural tube at 14.5 dpc (at protein level) (PubMed:21350012). Detected in the chorion and visceral endoderm between 6 and 8 dpc (PubMed:19056886). Detected in the visceral endoderm at 7 dpc, with a gradient from high expression in the anterior part to low expression at the posterior part (PubMed:19056886). At 8 dpc, detected in definitve endoderm, parts of the neuroectoderm, the headfold and posterior mesoderm (PubMed:19056886). Detected in the developing brain, the proepicardial organ and in somites at 8.5 dpc (PubMed:16872596, PubMed:18448090). At 9.5 and 10.5 dpc, detected in telencephalic vesicles, at the midbrain boundaries with forebrain and hindbrain, the hypothalamic region, in the apical ectodermal ridge, pharyngeal arches, the developing eye, the epithelial structures surrounding the lower region of the developing heart, limb buds and somites (PubMed:16872596, PubMed:18448090). At 10.5 dpc, detected at interlimb somites with loss of expression at limb somites and anterior trunk somites. At 11 dpc, detected in mesoderm in head and branchial arches, migrating germ cells and limbs (PubMed:16872596). Up-regulated by FGF2. N-glycosylated. Proteolytic cleavage in the juxtamembrane region gives rise to a soluble ectodomain. Cleavage is probably effected by a metalloprotease. Heterozygous mice are viable and fertile, but homozygous mice display nearly complete embryonic lethality. Most embryos die at about 10.5 dpc (PubMed:18448090, PubMed:19056886). A majority present disruption of the basement membrane and ruptures of the anterior visceral endoderm (PubMed:19056886). About one third display a pronounced defect in the fusion of the lateral edges of the body wall, resulting in cardia bifida. Mutant mice display also a defect in proepicardial cell migration. About one third of the mutants display abnormal morphogenesis of the neuroepithelium and headfold fusion defects. Besides, mutant embryos display defects in definitive endoderm migration, resulting in anterior axis truncations. Each of these phenotypes has partial penetrance, and many mutant embryos present a spectrum of defects. About 3% of the mutants develop into viable and fertile adults (PubMed:18448090, PubMed:19056886). Extended N-terminus.