ANKRD5: a key component of the axoneme required for sperm motility and male fertility
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Sperm motility is crucial for male reproduction and relies on the structural integrity of the sperm axoneme, which has a “9+2” microtubule configuration. This structure includes nine outer microtubule doublets that house various macromolecular complexes. The nexin-dynein regulatory complex (N-DRC) forms a crossbridge between the outer microtubule doublets, stabilizing them and facilitates sperm tail bending. Our investigation of ANKRD5, which is highly expressed in the sperm axoneme, reveals its interaction with TCTE1 and DRC4/GAS8, both key components of the N-DRC. The components of the N-DRC are often vital for sperm motility. ANKRD5 -/- mice exhibited reduced sperm motility and male infertility; however transmission electron microscopy and cryoelectron tomography showed no significant alterations in microtubule doublets. Moreover, ANKRD5 deficiency did not affect ATP levels, and its interactions with TCTE1 and DRC4/GAS8 were found to be independent of calcium regulation. These findings establish that ANKRD5 is critical for maintaining axoneme stability, which is important for sperm motility.
Significance Statement
Male infertility affects 8%-12% of men globally, with defects in sperm motility accounting for 40%-50% of these cases. The axoneme, serving as the sperm’s motor apparatus, features a 9+2 microtubule arrangement, with the nexin-dynein regulatory complex (N-DRC) providing essential structural support between outer microtubule doublets. Understanding the synergistic relationship between the N-DRC’s structure and its protein composition is crucial for advancing male reproductive biology. In this study, we identify the protein ANKRD5 as a component of the axoneme that can interact with N-DRC components, which is crucial for sperm motility. This discovery enhances our understanding of sperm motility mechanisms and suggests potential targets for male contraceptive development.
