Required for sperm development. Only expressed in the brain and developing sperm. Expression in the testes appears at approximately ten days of age and is maintained into adulthood, corresponding with the onset of meiosis. Expression in the testes appears limited to adluminal spermatids that are engaged in the assembly of flagella. Strong expression is observed in the spermatids within the lumen of the seminiferous tubules in testes from 8-week-old mice, but not in cells adjacent to the basement membrane of the tubule, including Sertoli cells, spermatogonia and spermatocytes. Not expressed in ovaries. Mice develop normally without obvious somatic defects but males are sterile due to malformation of the sperm flagella. Sperm cells display defects in the number and location of the head-tail coupling apparatus and lack flagellated sperm. Belongs to the CFAP73 family.