The function of SPEF2 (sperm flagellar and cilia associated 2, ENSG00000152582) is as follows. Required for correct axoneme development in spermatozoa. Important for normal development of the manchette and sperm head morphology. Essential for male fertility. Plays a role in localization of the intraflagellar transport protein IFT20 to the manchette, suggesting function as an adapter for dynein-mediated protein transport during spermatogenesis (PubMed:31048344, PubMed:31151990, PubMed:31278745). Plays a role in bone growth where it seems to be required for normal osteoblast differentiation (By similarity). Required for normal beat frequency of tracheal epithelial cilia and oviduct cilia (By similarity). {ECO:0000250|UniProtKB:Q8C9J3, ECO:0000269|PubMed:31048344, ECO:0000269|PubMed:31151990, ECO:0000269|PubMed:31278745}.