Seems to play a role in the development or function of the kidney glomerular filtration barrier. Regulates glomerular vascular permeability. May anchor the podocyte slit diaphragm to the actin cytoskeleton. Plays a role in skeletal muscle formation through regulation of myoblast fusion. Interacts with NPHS2 and with CD2AP (via C-terminal domain). Interacts with MAGI1 (via PDZ 2 and 3 domains) forming a tripartite complex with IGSF5/JAM4. Forms a complex with ACTN4, CASK, IQGAP1, MAGI2, SPTAN1 and SPTBN1 (By similarity). Interacts with DDN; the interaction is direct. Self-associates (via the Ig-like domains). Also interacts (via the Ig-like domains) with KIRREL1 and KIRREL2; the interaction with KIRREL1 is dependent on KIRREL1 glycosylation. Interacts with KIRREL3 (PubMed:15843475, PubMed:18752272). Located at podocyte slit diaphragm between podocyte foot processes. Expressed in kidney glomeruli. In the embryo, expressed in the mesonephric kidney at 11 dpc with strong expression in cranial tubules with podocyte-like structures. Expression is observed in the podocytes of the developing kidney from 13 dpc. High expression is also detected in the developing cerebellum, hindbrain, spinal cord, retina and hypothalamus. Expressed in skeletal muscle during myoblast fusion such as in the adult following acute injury and in the embryo but not detected in uninjured adult skeletal muscle. Isoform 1 and isoform 2 are expressed in the newborn brain and developing cerebellum. Isoform 1 is the predominant isoform in adult kidney. Phosphorylated at Tyr-1208 by FYN, leading to the recruitment and activation of phospholipase C-gamma-1/PLCG1. Death by postnatal day 2 associated with proteinuria, edema and massive glomerular vascular leak. Kidneys display enlarged Bowman's spaces, dilated tubuli, effacement of podocyte foot processes and an absence of the glomerular epithelial slit diaphragm. Impaired skeletal muscle development characterized by incomplete myoblast fusion. Belongs to the immunoglobulin superfamily.