Together with BCAR1 it may play a role in the control of epithelial cell polarity. Involved in the organization of apical junctions in kidney cells, together with NPHP4 and RPGRIP1L/NPHP8 (PubMed:21565611). Does not seem to be strictly required for ciliogenesis (PubMed:19208653). Seems to help to recruit PTK2B/PYK2 to cell matrix adhesions, thereby initiating phosphorylation of PTK2B/PYK2 and PTK2B/PYK2-dependent signaling (PubMed:11493697). May play a role in the regulation of intraflagellar transport (IFT) during cilia assembly (PubMed:19208653). Required for normal retina development (PubMed:19208653). In connecting photoreceptor cilia influences the movement of some IFT proteins such as IFT88 and WDR19 (PubMed:19208653). Involved in spermatogenesis; required for the differentiation of early elongating spermatids into spermatozoa (PubMed:18684731). Interacts with INVS and NPHP3 (By similarity). Interacts with Crk-associated substrate BCAR1 (PubMed:10739664, PubMed:11493697). Interacts with NPHP4 (By similarity). Interacts with PTK2B/PYK2 and tensin (PubMed:11493697). Interacts with AHI1 and TNK2 (By similarity). Interacts with NPHP4 in a complex containing NPHP1, NPHP4 and RPGRIP1L/NPHP8 (By similarity). Interacts with IQCB1; the interaction likely requires additional interactors (By similarity). Interacts (via SH3 domain) with PKD1 (PubMed:20856870). Interacts with KIF7 (By similarity). Interacts with ANKS3 (PubMed:25671767). Interacts with SPATA7 (PubMed:29899041). Interacts with FLNA (PubMed:12006559). In the retinal photoreceptor cell layer, localizes at the connecting cilium (PubMed:19208653, PubMed:29899041). Colocalizes with E-cadherin and BCAR1 at or near the cell-cell adherens junctions (PubMed:10739664). Localizes to respiratory cilia axoneme (PubMed:16885411). Localized to the transition zone of respiratory cilia (PubMed:16885411). Localized to the transition zone of photoreceptor-connecting cilia and renal monocilia (PubMed:16885411). In cultured renal cells, it localizes diffusely in the cytoplasm but, as cells approach confluence, it accumulates at basolateral tight junctions (PubMed:21565611). Expressed in the retina (at protein level) (PubMed:16885411, PubMed:19208653, PubMed:29899041). Expressed in the testis (at protein level) (PubMed:10665934). Widespread expression, with weak expression in skeletal muscle, kidney, thyroid, ovary, lung, prostate, thymus, uterus, heart, and liver (PubMed:10665934). Lowest levels in brain and spleen (PubMed:10665934). Widespread and uniform expression in whole embryo at all development stages (PubMed:10665934). Expressed in cell stages of the first meiotic division and thereafter (PubMed:10665934). Initially expressed at day 14 with consistent expression thereafter to day 365 (PubMed:18684731). The SH3 domain mediates the stable interaction with Cas and is involved in establishing tight junctions in epithelial cells. Mice are viable without renal manifestations of nephronophthisis (PubMed:18684731). Male mice are infertile with oligoteratozoospermia (PubMed:18684731). Spermatogenesis is blocked at the early stages of spermatid elongation, with degenerating spermatids sloughing off into the lumen (PubMed:18684731). Early elongating spermatids are detached from Sertoli cells and show a failure of sperm head and tail morphogenesis and an abnormal F-actin distribution (PubMed:18684731). Severe retinal degradation with mislocalized rhodopsin, disorganized outer segments, restricted expression of transducin to the inner segment and abnormal intraflagellar transport (IFT) of IFT57 (PubMed:19208653). Belongs to the nephrocystin-1 family.