Essential for normal retinal maturation and development (PubMed:10967074, PubMed:11273674, PubMed:11853760). Acts as a retinal cell surface receptor for NXNL1 and plays an important role in NXNL1-mediated survival of retinal cone photoreceptors (PubMed:25957687). 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 (PubMed:25957687). 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, SLC16A3 and SLC16A8 to the plasma membrane (PubMed:12601063). 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 (PubMed:23727514, PubMed:11882021). Interacts with NXNL1 (PubMed:25957687). Interacts with SLC2A1 and SLC16A1/GLUT1 (By similarity). Interacts with XKR8; promoting its localization at the cell membrane (PubMed:27503893). Interacts with ATP1B2, MAG and L1CAM (PubMed:12558975). Interacts with SLC16A1/GLUT1 and SLC16A7 (PubMed:21792931). Interacts with VEGFA, KDR/VEGFR2, PPIA/CYPA, SLC1A3, SLC16A11 and SLC16A12 (By similarity). Interacts with PPIL2; regulates BSG transport to the cell membrane (By similarity). Interacts with SLC16A3; interaction mediates SLC16A3 targeting to the plasma membrane (By similarity). Retina-specific (PubMed:12939332, PubMed:11273674, PubMed:11853760, PubMed:25957687). Expressed in both rods and cones (at protein level) (PubMed:25957687). Testis and caput, corpus and cauda epididymides (at protein level) (PubMed:11882021, PubMed:23727514, PubMed:21792931). Expressed in the brain, lung, liver, kidney, heart, spleen, uterus, retina and skeletal muscle (PubMed:2361961, PubMed:12939332, PubMed:12601063). In developing eye expressed at embryonic days 12 dpc, 15 dpc and 18 dpc, and at postnatal days P1, P7, P14, and P21. Expression progressed from a more generalized distribution throughout the undifferentiated neural retina to specific staining of retina-pigmented epithilia, the MCs, photoreceptor cells and the ciliary apparatus. Expression is highest at P21. Isoform 1 and isoform 2 are expressed at equivalent levels at P7, isoform 1 is more abundant at P14, P21 and P28. In uterus during the peri-implantation period strongly expressed in luminal and glandular epithelium on day 1 of pregnancy and gradually decreased to a basal level from day 2-4 of pregnancy. Expression in the sub-luminal stroma was first detected on day 3 of pregnancy and increased on day 4 of pregnancy. On day 5 of pregnancy, the expression of basigin protein and mRNA was only detected in the implanting embryos, and the luminal epithelium and sub-luminal stroma surrounding the embryos. In ovary during sexual maturation expressed in the granulosa cells of preantral follicles at days 20 and 25 after birth. Expressed during corpus luteum formation. By estrogen in the uterine epithelium of ovariectomized animals. By eCG in ovary. N-glycosylated. N-glycosylated (PubMed:12558975, PubMed:23727514). During spermatogenesis, probably deglycosylated during epididymal transit (PubMed:11882021). Male mice are sterile, testis lack elongated spermatids and mature spermatozoa, spermatogenesis is arrested at the early round spermatid stages before any spermatid differentiation occurrs and a large increase in the number of germ cells undergoing apoptosis is seen in the testis (PubMed:23727514). Mice are visually impaired at the time of eye opening (2 weeks of age), despite normal retina architecture at that age (PubMed:10967074, PubMed:11273674, PubMed:11853760). At visual maturity (3 weeks of age), the photoreceptor outer segments appear less dense and shorter than those of control animals, and at 8 weeks, retinal degeneration is observed (PubMed:10967074, PubMed:11273674, PubMed:11853760).