The mammalian sperm midpiece has a unique double-helical structure called the mitochondrial sheath that wraps tightly around the axoneme. Despite the remarkable organization of the mitochondrial sheath, the molecular mechanisms involved in mitochondrial sheath formation are unclear. In the process of screening testis-enriched genes for functions in mice, we identified armadillo repeat-containing 12 (ARMC12) as an essential protein for mitochondrial sheath formation. Here, we engineered Armc12-null mice, FLAG-tagged Armc12 knock-in mice, and TBC1 domain family member 21 (Tbc1d21)-null mice to define the functions of ARMC12 in mitochondrial sheath formation in vivo. We discovered that absence of ARMC12 causes abnormal mitochondrial coiling along the flagellum, resulting in reduced sperm motility and male sterility. During spermiogenesis, sperm mitochondria in Armc12-null mice cannot elongate properly at the mitochondrial interlocking step which disrupts abnormal mitochondrial coiling. ARMC12 is a mitochondrial peripheral membrane protein and functions as an adherence factor between mitochondria in cultured cells. ARMC12 in testicular germ cells interacts with mitochondrial proteins MIC60, VDAC2, and VDAC3 as well as TBC1D21 and GK2, which are required for mitochondrial sheath formation. We also observed that TBC1D21 is essential for the interaction between ARMC12 and VDAC proteins in vivo. These results indicate that ARMC12 uses integral mitochondrial membrane proteins VDAC2 and VDAC3 as scaffolds to link mitochondria and works cooperatively with TBC1D21. Thus, our studies have revealed that ARMC12 regulates spatiotemporal mitochondrial dynamics to form the mitochondrial sheath through cooperative interactions with several proteins on the sperm mitochondrial surface.

As the world population continues to increase to unsustainable levels, the importance of birth control and the development of new contraceptives are emerging. To date, male contraceptive options have been lagging behind those available to women, and those few options available are not satisfactory to everyone. To solve this problem, we have been searching for new candidate target proteins for non-hormonal contraceptives. Testis-specific proteins are appealing targets for male contraceptives because they are more likely to be involved in male reproduction and their targeting by small molecules is predicted to have no on-target harmful effects on other organs. Using in silico analysis, we identified Erich2, Glt6d1, Prss58, Slfnl1, Sppl2c, Stpg3, Tex33, and Tex36 as testis-abundant genes in both mouse and human. The genes, 4930402F06Rik and 4930568D16Rik, are testis-abundant paralogs of Glt6d1 that we also discovered in mice but not in human, and were also included in our studies to eliminate the potential compensation. We generated knockout (KO) mouse lines of all listed genes using the CRISPR/Cas9 system. Analysis of all of the individual KO mouse lines as well as Glt6d1/4930402F06Rik/4930568D16Rik TKO mouse lines revealed that they are male fertile with no observable defects in reproductive organs, suggesting that these 10 genes are not required for male fertility nor play redundant roles in the case of the 3 Glt6D1 paralogs. Further studies are needed to uncover protein function(s), but in vivo functional screening using the CRISPR/Cas9 system is a fast and accurate way to find genes essential for male fertility, which may apply to studies of genes expressed elsewhere. In this study, although we could not find any potential protein targets for non-hormonal male contraceptives, our findings help to streamline efforts to find and focus on only the essential genes.

Gamete fusion is a critical event of mammalian fertilization. A random one-bead one-compound combinatorial peptide library represented synthetic human egg mimics and identified a previously unidentified ligand as Fc receptor–like 3, named MAIA after the mythological goddess intertwined with JUNO. This immunoglobulin super family receptor was expressed on human oolemma and played a major role during sperm-egg adhesion and fusion. MAIA forms a highly stable interaction with the known IZUMO1/JUNO sperm-egg complex, permitting specific gamete fusion. The complexity of the MAIA isotype may offer a cryptic sexual selection mechanism to avoid genetic incompatibility and achieve favorable fitness outcomes.

The main pathological hallmark of Alzheimer's disease is the deposition of amyloid-beta (Aβ) peptides in the brain. Aβ has been widely used to mimic several aspects of Alzheimer's disease. However, several characteristics of amyloid-induced Alzheimer's disease pathology are not well established, especially in mice. The present study aimed to develop a new Alzheimer's disease model by investigating how Aβ can be effectively aggregated using prokaryotes and eukaryotes. To express the Aβ42 complex in HEK293 cells, we cloned the Aβ42 region in a tandem repeat and incorporated the resulting construct into a eukaryotic expression vector. Following transfection into HEK293 cells via lipofection, cell viability assay and western blotting analysis revealed that exogenous Aβ42 can induce cell death and apoptosis. In addition, recombinant His-tagged Aβ42 was successfully expressed in BL21 (DE3) and not only readily formed Aβ complexes, but also inhibited the proliferation of SH-SY5Y cells and. For in vivo testing, recombinant His-tagged Aβ42 solution (3 μg/μl in 1× PBS containing 1 mM Ni²⁺) was injected stereotaxically into the left and right lateral ventricles of the brains of C57BL/6J mice ( = 8). Control mice were injected with 1× PBS containing 1 mM Ni²⁺ following the same procedure. Ten days after the sample injection, the Morris water maze test confirmed that exogenous Aβ caused an increase in memory loss. These findings demonstrated that Ni²⁺ is capable of complexing the 50-kDa amyloid and that intracerebroventricular injection of Aβ42 can lead to cognitive impairment, thereby providing improved Alzheimer's disease models.

Glycosylphosphatidylinositol-anchored sperm hyaluronidases (HYAL) assist sperm penetration through the cumulus–oocyte complex (COC), but their role in mammalian fertilization remains unclear. Previously, we demonstrated that sperm from HYAL 5 and 7 double-knockout (dKO) mice produced significantly less offspring than sperm from wild-type mice due to defective COC dispersal. However, the HYAL6 gene remained active in the sperm from the dKO mice, indicating that they were not entirely infertile. This study explored the role of HYAL6 in fertilization by analyzing HYAL6-mutant mice. In this mouse model, HYAL5 and HYAL7 were present in the HYAL6-knockout sperm, and they could disperse hyaluronic acid. We found that HYAL6 was present on the surface of sperm. However, male mice lacking the HYAL6 gene had normal fertility, testicular integrity, and sperm characteristics. Furthermore, in vitro fertilization assays demonstrated that HYAL6-deficient epididymal sperm functioned normally. Therefore, HYAL6 is dispensable for fertilization.