Component of the nexin-dynein regulatory complex (N-DRC), a key regulator of ciliary/flagellar motility which maintains the alignment and integrity of the distal axoneme and regulates microtubule sliding in motile axonemes. Plays an important role in the assembly of the N-DRC linker (By similarity). Plays dual roles at both the primary (or non-motile) cilia to regulate hedgehog signaling and in motile cilia to coordinate cilia movement. Required for proper motile cilia functioning. Positively regulates ciliary smoothened (SMO)-dependent Hedgehog (Hh) signaling pathway by facilitating the trafficking of SMO into the cilium and the stimulation of SMO activity in a GRK2-dependent manner (PubMed:17366626, PubMed:21659505, PubMed:27472056). May play a role in the spermatozoa motility (PubMed:11751847). Component of the nexin-dynein regulatory complex (N-DRC) (By similarity). Interacts with microtubules (PubMed:17366626). Interacts with SMO (PubMed:21659505). Interacts (via coiled-coil domains) with RAB3B (in GTP-bound form) (PubMed:18396146). Interacts with DRC7 (PubMed:31961863). Associates with microtubules (PubMed:17366626). Localized to the cytoplasm of round spermatids, the tails of elongating spermatids, and mature spermatid tail bundles protruding into the lumen, and in the flagellum of epididymal spermatozoa (PubMed:11751847). Highly expressed in adult testes and lung. Weakly or not expressed in other tested tissues. Weakly or not expressed in neonates and young adolescents. Then, it is strongly expressed postmeiotically. Accumulates in gametocytes as they approach the lumen of seminiferous tubules and thereafter. Expressed during serum starvation or contact inhibition of cells grown in murine fibroblasts. Mice show primary ciliary dyskinesia (PCD) like symptoms including situs inversus and hydrocephalus. Hydrocephalus starts at postnatal day 5 (P5) and becomes more pronounced as the mice mature, eventually leading to mortality between P14-P21. Development of hydrocephalus is associated with severe impairment of cilia motility on ependymal cells lining the ventricles of the brain. Belongs to the DRC4 family.