This family includes the radial spoke head proteins RSP4 and RSP6 from Chlamydomonas reinhardtii, and several eukaryotic homologues, including mammalian RSHL1, the protein product of a familial ciliary dyskinesia candidate gene []. The radial spoke head proteins are important in maintaining normal movement in motile, "9+2"-structure cilia and flagella. Mutations of the human RSPH9 and RSPH4A genes have been linked to primary ciliary dyskinesia, a genetically heterogeneous inherited disorder arising from dysmotility of motile cilia and sperm []. RSPH6A has also been shown to be required for sperm flagellum formation and male fertility in mice [].
