CRISPR/Cas mediated genome editing has been successfully demonstrated in mammalian cells and further applications for generating mutant mice were reported by injecting humanized Cas9 (hCas) mRNA and ...single guide RNA into fertilized eggs. Here we inject the circular plasmids expressing hCas9 and sgRNA into mouse zygotes and obtained mutant mice within a month. When we targeted the Cetn1 locus, 58.8% (10/17) of the pups carried the mutations and six of them were homozygously mutated. Co-injection of the plasmids targeting different loci resulted in the successful removal of the flanked region in two out of three mutant pups. The efficient mutagenesis was also observed at the Prm1 locus. Among the 46 offspring carrying CRISPR/Cas plasmid mediated mutations, only two of them carried the hCas9 transgene. The pronuclear injection of circular plasmid expressing hCas9/sgRNA complex is a rapid, simple, and reproducible method for targeted mutagenesis.
The mitochondrial sheath is composed of mitochondria that coil tightly around the midpiece of sperm flagellum. These mitochondria are recruited from the cytoplasm to the flagellum late in ...spermatogenesis. Initially, recruited mitochondria are spherical-shaped but then elongate laterally to become crescent-like in shape. Subsequently, crescent-like mitochondria elongate continuously to coil tightly around the flagellum. Recently, disorganization of the mitochondrial sheath was reported in Glycerol kinase 2 (Gk2) disrupted mice. To analyze the disorganization of the mitochondrial sheath further, we generated Gk2-deficient mice using the CRISPR/Cas9 system and observed sperm mitochondria in testis using a freeze-fracture method with scanning electron microscopy. Gk2-disrupted spermatids show abnormal localization of crescent-like mitochondria, in spite of the initial proper alignment of spherical mitochondria around the flagellum, which causes abnormal mitochondrial sheath formation leading to exposure of the outer dense fibers. These results indicate that GK2 is essential for proper arrangement of crescent-like mitochondria to form the mitochondrial sheath during mouse spermatogenesis.
The PIWI (P-element-induced wimpy testis)-interacting-RNA (piRNA) pathway plays a crucial role in the repression of TE (transposable element) expression via de novo DNA methylation in mouse embryonic ...male germ cells. Various proteins, including MIWI2 are involved in the process. TE silencing is ensured by piRNA-guided MIWI2 that recruits some effector proteins of the DNA methylation machinery to TE regions. However, the molecular mechanism underlying the methylation is complex and has not been fully elucidated. Here, we identified MORC3 as a novel associating partner of MIWI2 and also a nuclear effector of retrotransposon silencing via piRNA-dependent de novo DNA methylation in embryonic testis. Moreover, we show that MORC3 is important for transcription of piRNA precursors and subsequently affects piRNA production. Thus, we provide the first mechanistic insights into the role of this effector protein in the first stage of piRNA biogenesis in embryonic TE silencing mechanism.
Sperm malformation is a direct factor for male infertility. Multiple morphological abnormalities of the flagella (MMAF), a severe form of asthenoteratozoospermia, are characterized by immotile ...spermatozoa with malformed and/or absent flagella in the ejaculate. Previous studies indicated genetic heterogeneity in MMAF. To further define genetic factors underlying MMAF, we performed whole-exome sequencing in a cohort of 90 Chinese MMAF-affected men. Two cases (2.2%) were identified as carrying bi-allelic missense DNAH8 variants, variants which were either absent or rare in the control human population and were predicted to be deleterious by multiple bioinformatic tools. Re-analysis of exome data from a second cohort of 167 MMAF-affected men from France, Iran, and North Africa permitted the identification of an additional male carrying a DNAH8 homozygous frameshift variant. DNAH8 encodes a dynein axonemal heavy-chain component that is expressed preferentially in the testis. Hematoxylin-eosin staining and electron microscopy analyses of the spermatozoa from men harboring bi-allelic DNAH8 variants showed a highly aberrant morphology and ultrastructure of the sperm flagella. Immunofluorescence assays performed on the spermatozoa from men harboring bi-allelic DNAH8 variants revealed the absent or markedly reduced staining of DNAH8 and its associated protein DNAH17. Dnah8-knockout male mice also presented typical MMAF phenotypes and sterility. Interestingly, intracytoplasmic sperm injections using the spermatozoa from Dnah8-knockout male mice resulted in good pregnancy outcomes. Collectively, our experimental observations from humans and mice demonstrate that DNAH8 is essential for sperm flagellar formation and that bi-allelic deleterious DNAH8 variants lead to male infertility with MMAF.
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
-null mice, FLAG-tagged
knock-in mice, and TBC1 domain family member 21 (
)-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
-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.
The acrosome is a cap-shaped, Golgi-derived membranous organelle that is located over the anterior of the sperm nucleus and highly conserved throughout evolution. Although morphological changes ...during acrosome biogenesis in spermatogenesis have been well described, the molecular mechanism underlying this process is still largely unknown. Family with sequence similarity 71, member F1 and F2 (FAM71F1 and FAM71F2) are testis-enriched proteins that contain a RAB2B-binding domain, a small GTPase involved in vesicle transport and membrane trafficking. Here, by generating mutant mice for each gene, we found that Fam71f1 is essential for male fertility. In Fam71f1-mutant mice, the acrosome was abnormally expanded at the round spermatid stage, likely because of enhanced vesicle trafficking. Mass spectrometry analysis after immunoprecipitation indicated that, in testes, FAM71F1 binds not only RAB2B, but also RAB2A. Further study suggested that FAM71F1 binds to the GTP-bound active form of RAB2A/B, but not the inactive form. These results indicate that a complex of FAM71F1 and active RAB2A/B suppresses excessive vesicle trafficking during acrosome formation.
Transmembrane protein 16E (TMEM16E) belongs to the TMEM16 family of proteins that have 10 transmembrane regions and appears to localize intracellularly. Although TMEM16E mutations cause bone ...fragility and muscular dystrophy in humans, its biochemical function is unknown. In the TMEM16 family, TMEM16A and -16B serve as Ca
2+
-dependent Cl
−
channels, while TMEM16C, -16D, -16F, -16G, and -16J support Ca
2+
-dependent phospholipid scrambling. Here, we show that TMEM16E carries a segment composed of 35 amino acids homologous to the scrambling domain in TMEM16F. When the corresponding segment of TMEM16A was replaced by this 35-amino-acid segment of TMEM16E, the chimeric molecule localized to the plasma membrane and supported Ca
2+
-dependent scrambling. We next established TMEM16E-deficient mice, which appeared to have normal skeletal muscle. However, fertility was decreased in the males. We found that TMEM16E was expressed in germ cells in early spermatogenesis and thereafter and localized to sperm tail. TMEM16E
−/−
sperm showed no apparent defect in morphology, beating, mitochondrial function, capacitation, or binding to zona pellucida. However, they showed reduced motility and inefficient fertilization of cumulus-free but zona-intact eggs in vitro. Our results suggest that TMEM16E may function as a phospholipid scramblase at inner membranes and that its defect affects sperm motility.
Infertility is a global health issue that affects 1 in 6 couples, with male factors contributing to 50% of cases. The flagellar axoneme is a motility apparatus of spermatozoa, and disruption of its ...structure or function could lead to male infertility. The axoneme consists of a “9+2” structure that contains a central pair of two singlet microtubules surrounded by nine doublet microtubules, in addition to several macromolecular complexes such as dynein arms, radial spokes, and nexin-dynein regulatory complexes. Molecular components of the flagellar axoneme are evolutionally conserved from unicellular flagellates to mammals, including mice. Although knockout (KO) mice have been generated to understand their function in the formation and motility regulation of sperm flagella, the majority of KO mice die before sexual maturation due to impaired ciliary motility, which makes it challenging to analyze mature spermatozoa. In this review, we introduce methods that have been used to overcome premature lethality, focusing on KO mouse lines of central pair components.
Although several long noncoding RNAs (lncRNAs) have recently been shown to encode small polypeptides, those in testis remain largely uncharacterized. Here we identify two sperm-specific polypeptides, ...Kastor and Polluks, encoded by a single mouse locus (Gm9999) previously annotated as encoding a lncRNA. Both Kastor and Polluks are inserted in the outer mitochondrial membrane and directly interact with voltage-dependent anion channel (VDAC), despite their different amino acid sequences. Male VDAC3-deficient mice are infertile as a result of reduced sperm motility due to an abnormal mitochondrial sheath in spermatozoa, and deficiency of both Kastor and Polluks also severely impaired male fertility in association with formation of a similarly abnormal mitochondrial sheath. Spermatozoa lacking either Kastor or Polluks partially recapitulate the phenotype of those lacking both. Cooperative function of Kastor and Polluks in regulation of VDAC3 may thus be essential for mitochondrial sheath formation in spermatozoa and for male fertility.
Immunity-related GTPases (IRGs), also known as p47 GTPases, are a family of interferon-inducible proteins that play roles in immunity defense against intracellular pathogens. Although the molecular ...functions of IRGs have been well studied, the function of the family member, IRGC1, remains unclear. IRGC1 is unique among IRGs because its expression is not induced by interferon and it is expressed predominantly in the testis. Further, IRGC1 is well conserved in mammals unlike other IRGs. Here, we knocked out (KO) Irgc1 in mice using the CRISPR/Cas9 system and found that the fertility of Irgc1 KO males was severely impaired because of abnormal sperm motility. Further analyses with a transmission electron microscope revealed that the fibrous sheath (FS), an accessory structure of the sperm tail, was disorganized in Irgc1 KO mice. In addition, IRGC1 was detected in the sperm tail and fractionated with FS proteins. These results suggest that IRGC1 is a component of the FS and is involved in the correct formation of the FS.
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•IRGC1, a testis-enriched immunity related GTPase, is important for male fertility in mice.•Irgc1 KO mice exhibited impaired sperm motility.•Fibrous sheath structures were disrupted in Irgc1 KO spermatozoa.•IRGC1 fractionates with fibrous sheath proteins, suggesting that IRGC1 is a component of the fibrous sheath.
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