May play a role in the control of meiotic division and germ cell differentiation through regulation of pairing and recombination during meiosis. Required for sperm flagella assembly (PubMed:22396656). May play a role in the assembly and function of the outer dynein arm-docking complex (ODA-DC). ODA-DC mediates outer dynein arms (ODA) binding onto the axonemal doublet microtubules (By similarity). Able to form oligomers (PubMed:22396656). Interacts with ODAD1 (By similarity). Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme. High expression in testis (PubMed:22396656). Expressed in pachytene spermatocytes and post-meiotic spermatids (PubMed:8032679, PubMed:22396656). Expressed in the ventral embryonic node at developmental stage 8 dpc. MNS1-deficient mice display situs inversus and hydrocephalus. They are sterile, exhibit a sharp reduction in sperm production, and remnant spermatozoa are immotile with abnormal short tails. Belongs to the MNS1 family.