Cfap97d1 is important for flagellar axoneme maintenance and male mouse fertility

The flagellum is essential for sperm motility and fertilization in vivo. The axoneme is the main component of the flagella, extending through its entire length. An axoneme is comprised of two central microtubules surrounded by nine doublets, the nexin-dynein regulatory complex, radial spokes, and dynein arms. Failure to properly assemble components of the axoneme in a sperm flagellum, leads to fertility alterations. To understand this process in detail, we have defined the function of an uncharacterized gene, Cfap97 domain containing 1 (Cfap97d1). This gene is evolutionarily conserved in mammals and multiple other species, including Chlamydomonas. We have used two independently generated Cfap97d1 knockout mouse models to study the gene function in vivo. Cfap97d1 is exclusively expressed in testes starting from post-natal day 20 and continuing throughout adulthood. Deletion of the Cfap97d1 gene in both mouse models leads to sperm motility defects (asthenozoospermia) and male subfertility. In vitro fertilization (IVF) of cumulus-intact oocytes with Cfap97d1 deficient sperm yielded few embryos whereas IVF with zona pellucida-free oocytes resulted in embryo numbers comparable to that of the control. Knockout spermatozoa showed abnormal motility characterized by frequent stalling in the anti-hook position. Uniquely, Cfap97d1 loss caused a phenotype associated with axonemal doublet heterogeneity linked with frequent loss of the fourth doublet in the sperm stored in the epididymis. This study demonstrates that Cfap97d1 is required for sperm flagellum ultra-structure maintenance, thereby playing a critical role in sperm function and male fertility in mice.
Author summary Infertility is a growing issue in modern society, affecting about 15% of reproductive age couples. About 1 in 20 men of reproductive age has fertility issues. The causes of male infertility remain undefined in more than half of the cases. Approximately one-fourth of male infertility cases can be attributed to genetic factors. Currently, only a few genes involved in testis development and sperm formation have been well studied and shown to have clinical significance. A better understanding of male fertility mechanisms will help to advance infertility treatments and the development of additional contraceptive alternatives, including those targeting male sex cells. Testes uniquely express several hundreds of genes and the functions of numerous testis-specific genes are yet uncharacterized. We have identified the evolutionarily conserved Cfap97d1 gene as a testis-specific gene in a public database screen. We used two knockout mouse models to demonstrate that the absence of the Cfap97d1 gene causes reduced sperm motility (asthenozoospermia) due to destabilization of outer microtubule doublet in sperm flagellum. This research shows that Cfap97d1 is an important regulator of male fertility.