LRRC23 is a conserved component of the radial spoke that is necessary for sperm motility and male fertility in mice.

Cilia and flagella are ancient structures that achieve controlled motor functions through the coordinated interaction based on microtubules, and some attached projections. Radial spokes (RSs) facilitate the beating motion of these organelles by mediating signal transduction between dyneins and a central pair (CP) of singlet microtubules. RS complex isolation from Chlamydomonas axonemes enabled the detection of 23 radial spoke proteins (RSP1-23), with the roles of some radial spoke proteins remained unknown. Recently, RSP15 has been reported to be located to the stalk of RS2, but its homolog in mammals has not been explored. Herein, we show that Lrrc23 is an evolutionarily conserved testis-enriched gene encoding an RSP15 homolog in mice. We found that LRRC23 localizes to the RS complex within murine sperm flagella and interacts with RSPH3A/B. The knockout of Lrrc23 resulted in male infertility due to RS disorganization and impaired motility in murine spermatozoa, whereas the ciliary beating was unaffected significantly. These data indicate that LRRC23 is a key regulator underpinning the integrity of RS complex within the flagella of mammalian spermatozoa, whereas it is dispensable in cilia.