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). Self-associates (via the Ig-like domains). Also interacts (via the Ig-like domains) with KIRREL1/NEPH1 and KIRREL2; the interaction with KIRREL1 is dependent on KIRREL1 glycosylation. Interacts with KIRREL3 (By similarity). Interacts with MAGI1 (via PDZ 2 and 3 domains) forming a tripartite complex with IGSF5/JAM4. Interacts with DDN; the interaction is direct. Forms a complex with ACTN4, CASK, IQGAP1, MAGI2, SPTAN1 and SPTBN1. Located at podocyte slit diaphragm between podocyte foot processes. Experimental confirmation may be lacking for some isoforms. Strongly expressed in the podocytes of kidney glomeruli (at protein level) and at lower levels in the spleen. Following injection with puromycin which induces nephrosis, down-regulated by 40% 3 days post-injection and by 80% at day 10. Also down-regulated by HgCl2 with rapid decrease at day 3. Phosphorylated at Tyr-1204 by FYN, leading to the recruitment and activation of phospholipase C-gamma-1/PLCG1. Belongs to the immunoglobulin superfamily.