CCDC183 is essential for cytoplasmic invagination around the flagellum during spermiogenesis and male fertility

Sperm flagellum plays a crucial role in male fertility. Here, we generated Ccdc183 knockout mice using the CRISPR/Cas9 system to reveal the protein function of the testis-specific protein CCDC183 in spermiogenesis. We demonstrated that the absence of CCDC183 causes male infertility with morphological and motility defects in spermatozoa. Owing to the lack of CCDC183, centrioles after elongation of axonemal microtubules do not connect the cell surface and nucleus during spermiogenesis, which causes subsequent loss of cytoplasmic invagination around the flagellum. As a result, the flagellar compartment does not form properly and cytosol-exposed axonemal microtubules collapse during spermiogenesis. In addition, ectopic localization of accessory structures, such as the fibrous sheath and outer dense fibers, and abnormal head shape as a result of abnormal sculpting by the manchette are observed in Ccdc183 knockout spermatids. Our results indicate that CCDC183 plays an essential role in cytoplasmic invagination around the flagellum to form functional spermatozoa during spermiogenesis.

Exposure of spermatozoa to dibutyl phthalate induces abnormal embryonic development in a marine invertebrate Galeolaria caespitosa (Polychaeta: Serpulidae)

In this study, we have investigated the impact of dibutyl phthalate (DBP) on early embryogenesis in a sessile marine invertebrate, Galeolaria caespitosa. DBP was found to induce sperm dysfunction as well as impaired and defective embryogenesis characterised by a particular pattern of abnormality. Thus, after the first cleavage, one blastomere in these abnormal embryos was able to carry out further mitoses, while the other arrested. Analysis of microtubules, chromosomes and actin filaments demonstrated that the mitotic spindles in the abnormal embryos were irregularly bent, shortened and unable to anchor to the cortex, resulting in the defective segregation of chromosomes. Within the non-dividing blastomeres, karyokinesis was found to continue at a slow pace as indicated by the presence of multiple sets of abnormal mitotic spindles. However, cytokinesis had been disrupted in these arrested cells due to a failure to assemble the contractile actin ring, as a result of which one pole of the embryos remained as one large, undivided cell. DBP was found to suppress the activity of superoxide dismutase in spermatozoa and, in association with this change, DBP-treated cells experienced oxidative stress as indicated by the presence of lipid aldehydes, such as 4-hydroxynonenal (4-HNE) in the sperm acrosome and neck. Adduction of lipid aldehydes at the level of the acrosome would be expected to impede the acrosome reaction and account for the significant decrease in fertilisation rates. 4-HNE generated as a consequence of lipid peroxidation in the sperm neck resulted in alkylation of the sperm centrioles. Such paternally damaged centrioles were inherited by the embryos and disrupted cytoskeletal protein organisation during early cleavage, generating the observed abnormalities in embryonic development. This research emphasises the vulnerability of spermatozoa to oxidative damage and highlights novel potential mechanisms for reproductive toxicity involving the alkylation of subcellular structures in spermatozoa by lipid aldehydes.