Axoneme preparation Bovine sperm Frozen bovine sperm was obtained from the Utrecht University Veterinary Faculty and was prepared for cryo-EM as previously described2. Briefly, sperm straws were thawed by immersion in a 37 °C water bath for about 30 s. Sperm were then washed twice with Dulbecco’s PBS (Sigma), counted and diluted to concentrations of approximately 0.1–0.2 × 106 […]