In mice carrying the autosomal recessive mutation ‘abnormal spermatozoon head shape’ ( azh ) all spermatozoa display a highly abnormal head morphology that differs drastically from the compact and hook-shaped head of the normal murine sperm. Moreover, the azh mutation causes tail abnormalities often resulting in coiled sperm tails or in the decapitation of the sperm head from the flagellum. We have isolated and characterized murine Hook1 cDNA and analyzed the corresponding genomic structure. Furthermore, the Hook1 gene was mapped to the same region on chromosome 4 to which the azh locus was previously linked. The Hook1 gene is predominantly expressed in haploid male germ cells, and immunohistochemical analysis revealed that Hook1 is responsible for the linkage of the microtubular manchette and the flagellum to cellular structures. Here, we report that the azh mutation is due to a deletion of exons 10 and 11 in the murine Hook1 gene leading to a non-functional protein. Our results indicate that loss of Hook1 function results in ectopic positioning of microtubular structures within the spermatid and causes the azh phenotype. Therefore, the human HOOK1 gene could serve as a candidate gene for male infertility due to teratozoospermia or decapitation defects.

Impaired ciliary and flagellar functions resulting in male infertility and recurrent respiratory tract infections are found in patients suffering from primary ciliary dyskinesia (PCD). In most cases, axonemal defects are present, i.e. PCD patients often lack inner and/or outer dynein arms in their sperm tails and cilia, supporting the hypothesis that mutations in dynein genes may cause PCD. However, to date it is unclear whether mutations in dynein heavy chain genes are responsible for impaired flagellar and ciliary motility in mammals. To elucidate the role of the mouse dynein heavy chain 7 (MDHC7) gene, which encodes a component of the inner dynein arm, we have generated mice lacking this dynein heavy chain isoform. Both MDHC7^+/– and MDHC7^–/– mice are viable and show no malformations; however, homozygous males produce no offspring. In comparison to MDHC7^+/– and wild-type mice the spermatozoa of MDHC7^–/– mice revealed a dramatic reduced straight line velocity and progressive movement, resulting in the inability of MDHC7-deficient sperm to move from the uterus into the oviduct. Additionally, we measured the beat frequency of tracheal cilia and observed a decrease in the beat frequency of ∼50% in MDHC7^–/– mice. The reduction in both ciliary and flagellar motility is not correlated with any gross defects in the axonemal structure. The phenotype of MDHC7^–/– mice is similar to that observed in some patients suffering from PCD, and our data strongly suggest that in some patients this disease could be due to mutations in the homologous human gene DNAH1 (HDHC7).

In recent years, optical genome mapping (OGM) has developed into a highly promising method of detecting large-scale structural variants in human genomes. It is capable of detecting structural variants considered difficult to detect by other current methods. Hence, it promises to be feasible as a first-line diagnostic tool, permitting insight into a new realm of previously unknown variants. However, due to its novelty, little experience with OGM is available to infer best practices for its application or to clarify which features cannot be detected. In this study, we used the Saphyr system (Bionano Genomics, San Diego, CA, USA), to explore its capabilities in human genetic diagnostics. To this end, we tested 14 DNA samples to confirm a total of 14 different structural or numerical chromosomal variants originally detected by other means, namely, deletions, duplications, inversions, trisomies, and a translocation. Overall, 12 variants could be confirmed; one deletion and one inversion could not. The prerequisites for detection of similar variants were explored by reviewing the OGM data of 54 samples analyzed in our laboratory. Limitations, some owing to the novelty of the method and some inherent to it, were described. Finally, we tested the successful application of OGM in routine diagnostics and described some of the challenges that merit consideration when utilizing OGM as a diagnostic tool.

The sperm mitochondria-associated cysteine-rich protein (SMCP) is a cysteine- and proline-rich structural protein that is closely associated with the keratinous capsules of sperm mitochondria in the mitochondrial sheath surrounding the outer dense fibers and axoneme. To investigate the function of SMCP, we generated mice with a targeted disruption of the gene Smcp by homologous recombination. Homozygous mutant males on a mixed genetic background (C57BL/6J × 129/Sv) are fully fertile, while they are infertile on the 129/Sv background, although spermatogenesis and mating are normal. Homozygous Smcp^−/− female mice are fertile on both genetic backgrounds. Electron microscopical examination demonstrated normal structures of sperm head, mitochondria, and tail. In vivo experiments with sperm of Smcp^−/− 129/Sv mice revealed that the migration of spermatozoa from the uterus into the oviduct is reduced. This result is supported by the observation that sperm motility as determined by the computer-assisted semen analysis system (CASA) is significantly affected as compared to wild-type spermatozoa. In vitro fertilization assays showed that Smcp-deficient spermatozoa are able to bind to the oocyte but that the number of fertilized eggs is reduced by more than threefold relative to the wild-type control. However, removal of the zona pellucida resulted in an unaffected sperm-egg fusion which was monitored by the presence of pronuclei and generation of blastocyts. These results indicate that the infertility of the male Smcp^−/− mice on the 129/Sv background is due to reduced motility of the spermatozoa and decreased capability of the spermatozoa to penetrate oocytes.