Essential for normal retinal maturation and development (By similarity). Acts as a retinal cell surface receptor for NXNL1 and plays an important role in NXNL1-mediated survival of retinal cone photoreceptors (By similarity). In association with glucose transporter SLC16A1/GLUT1 and NXNL1, promotes retinal cone survival by enhancing aerobic glycolysis and accelerating the entry of glucose into photoreceptors (By similarity). Signaling receptor for cyclophilins, essential for PPIA/CYPA and PPIB/CYPB-dependent signaling related to chemotaxis and adhesion of immune cells (By similarity). Plays an important role in targeting the monocarboxylate transporters SLC16A1/GLUT1 and SLC16A3 to the plasma membrane (PubMed:10921872). Acts as a coreceptor for vascular endothelial growth factor receptor 2 (KDR/VEGFR2) in endothelial cells enhancing its VEGFA-mediated activation and downstream signaling (By similarity). Promotes angiogenesis through EPAS1/HIF2A-mediated up-regulation of VEGFA and KDR/VEGFR2 in endothelial cells (By similarity). Plays an important role in spermatogenesis; mediates interactions between germ cells and Sertoli cell and is essential for the development/differentiation of germ cells to round spermatids (By similarity). Homooligomer (By similarity). Interacts with NXNL1, SLC2A1 and SLC16A1/GLUT1 (By similarity). Interacts with XKR8; promoting its localization at the cell membrane (By similarity). Homooligomer (Probable). Interacts with SLC16A1/GLUT1 (PubMed:10921872). Interacts with SLC16A3; interaction mediates SLC16A3 targeting to the plasma membrane (PubMed:11719518). Interacts with VEGFA, KDR/VEGFR2, PPIA/CYPA, SLC16A12, SLC16A11, ATP1B2, MAG, L1CAM and AJAP1 (By similarity). Interacts with PPIL2; regulates BSG transport to the cell membrane (By similarity). Expressed in the skeletal muscle, liver, small intestine, kidney, testis, brain, heart and spleen (PubMed:8425897). Also present in various immature cells and endothelia (PubMed:2009910). In uterus during peri-implantation period strongly expressed in the luminal epithelium on day 1 of pregnancy and gradually decreased to a basal concentration from day 3 to day 5 of pregnancy. Strongly expressed in the implanting blastocyst and primary decidua on day 6 of pregnancy. By activation of lymphocytes by mitogens. By estrogen in the uterine epithelium of ovariectomized animals.