Mutations in AK9 impair male fertility by altering sperm motility in mice and cattle.
Despite passing routine laboratory tests for semen quality, bulls used in artificial insemination (AI) can exhibit a significant variation in fertility. During fertility analysis, a subfertile bull with a low pregnancy rate of 10% was identified. To fully characterize the phenotype, a range of in vitro, in vivo and molecular assays were carried out. Additionally, knockout mice were generated to investigate the function of the identified mutated gene. Sperm from the subfertile bull exhibited reduced motility and severely reduced caffeine-induced hyperactivation compared to control bulls of proven fertility. Ability to penetrate the zona pellucida, cleavage rate, cleavage kinetics, and blastocyst yield after IVF or AI were significantly lower than in control bulls. Whole-genome sequencing and RNA sequencing of testis revealed a critical mutation in AK9 that affect splicing, shaping the majority of AK9 transcripts that leads to a premature termination codon and a severely truncated protein. Transgenic mice deficient in AK9 were generated, resulting in the production of immotile sperm that were unable to fertilize the oocyte. These sperm exhibited abnormalities, including a low ATP concentration. RNA-seq analysis of testis revealed differential gene expression of components of the axoneme and sperm flagella, as well as steroid metabolic processes. Sperm ultrastructural analysis showed a higher percentage of sperm with abnormal flagella. The infertility produced by AK9 mutant bull and in AK9 deficient mice indicates the essential metabolic role of AK9 in sperm motility and/or hyperactivation, which in turn affects sperm binding and penetration of the zona pellucida. Overall design: Differential gene expression analysis in mice Ak9 knockout testis compared to wild-type testis.