Flagellar protein involved in sperm flagellum axoneme organization and function. Expressed in testis. Mice are viable and show no malformations. However, homozygous males exhibit complete male sterility due to severe defects in sperm mobility. Sperm from mutant mice is characterized by normal flagellum length, but most of them showed abnormal forms and irregular caliber of the midpiece. Females are fertile and give litters of normal size. Belongs to the CFAP44 family.