CCDC89 is required for optimal sperm motility and male fertility in mammals

STUDY QUESTION: What is the role of coiled-coil domain-containing protein 89 (CCDC89) in mammalian male fertility?

SUMMARY ANSWER: The presence of CCDC89 is required for normal sperm motility and therefore optimal male fertility in mice, while CCDC89 variants affected spermatogenesis in both mice and humans.

WHAT IS KNOWN ALREADY: Coiled-coiled domain-containing proteins play a variety of roles in biological processes, including cell division, the production of motile sperm, and the regulation of their motility.

STUDY DESIGN, SIZE, DURATION: DNA from infertile men with azoospermia was sequenced to identify genetic variants as per the Genetics of Male Infertility Initiative (GEMINI) study. Genetic variants were identified in CCDC89 in three men, by whole exome sequencing. A testis biopsy from infertile Patient 1 (CCDC89 variant c. G903T) was available and used to inspect tissue pathology. Ccdc89 knockout (Ccdc89-/-) and Ccdc89E297D/E297D mutant mouse models were generated to define the role of CCDC89 in male fertility and the role of the specific CCDC89 genetic variant, c. G903T, in the pathogenesis of infertility.

PARTICIPANTS/MATERIALS, SETTING, METHODS: CCDC89 RNA expression and protein localization were investigated in a testis biopsy from a control male with normal spermatogenesis. Male fertility of the mutant mouse lines was assessed via breeding, histology, daily sperm production, electron microscopy, computer-assisted and high-speed sperm motility analysis, and in vitro fertilization.

MAIN RESULTS AND THE ROLE OF CHANCE: Ccdc89-/- male mice were sub-fertile, with impaired progressive sperm motility and curvilinear velocity due to a rigid sperm tail midpiece without any overt structural defects. While Ccdc89E297D/E297D males were fertile, their testis weights and germ cell content were reduced, suggesting a potential role of the c. G903T variant, observed in each of the two men, in the pathogenesis of their spermatogenic impairment. We also identified a new genetic variant in CCDC89 (c.G1024A) in another infertile man, that was in trans with the c. G903T genetic variant.

LARGE SCALE DATA: N/A.

LIMITATIONS, REASONS FOR CAUTION: The identification of additional infertile men with genetic variants in CCDC89, and quality clinical data, are required to determine prognostic reliability regarding CCDC89 variants. There are likely to be species-specific differences in gene function.

WIDER IMPLICATIONS OF THE FINDINGS: Our data highlight a role for CCDC89, in regulating the sperm tail waveform, that is required for optimal sperm fertilization capacity and male fertility. We highlight CCDC89 as a regulator of male fertility in mammals, where variants in CCDC89 can affect spermatogenesis and may be a risk factor for human male infertility. This study underscores the importance of validating clinical genetic findings.

STUDY FUNDING/COMPETING INTEREST(S): This work was supported by a National Health and Medical Research Council grant (APP1120356), National Institutes of Health grants (R01HD078641 and P50HD096723), the Novo Nordisk Foundation (grant numbers NNF210C0069913 and NNF21C0069969), the Capital Region of Denmark, the Independent Research Fund (grant number: 1030-00381B), and the Svend Andersen Foundation (grant number: 84-A.08), and the Christian and Ottilia Brorsons (No. 12038-1) and Frimodt-Heineke Foundation travel grants for research exchange. The authors have no conflicts of interest.