Microtubule Inner Protein CFAP77 Contributes to Sperm Motility and Male Fertility in Mice

Background Sperm motility is essential for male fertility, and its regulation is dependent on the structural integrity of the axoneme. The axoneme consists of a conserved “9+2” microtubule arrangement and is supported by microtubule inner proteins. However, the functional significance of many microtubule inner proteins remains unclear. Cilia‐ and flagella‐associated protein 77 (CFAP77) has been identified as a microtubule inner protein in various species, but its role in mammalian sperm function has not been fully elucidated. Objectives This study aims to investigate the function of CFAP77 in sperm motility and male fertility using a Cfap77 knockout mouse model. Materials and Methods Cfap77 knockout mice were generated using the CRISPR‐Cas9 system. Male fertility was assessed by mating tests, and sperm motility was analyzed using computer‐assisted sperm analysis. Immunoblotting and immunoprecipitation‐mass spectrometry were performed to determine CFAP77's localization and interaction with other microtubule inner proteins. Results We found that CFAP77 localized to the sperm flagella in mice. Moreover, Cfap77 knockout males exhibited significantly reduced fertility, with impaired sperm motility despite normal morphology. Immunoprecipitation‐mass spectrometry analysis revealed that CFAP77 interacts with TEKTL1, and CFAP77 loss leads to a reduced amount of TEKTL1 in spermatozoa. Discussion and Conclusion We demonstrate that CFAP77 is crucial for sperm motility and male fertility. The interaction between CFAP77 and other microtubule inner proteins suggests a role in stabilizing other microtubule inner proteins and regulating flagellar function. These results provide insights into the molecular mechanisms of sperm motility regulation.