Mutations in a Novel Locus on Mouse Chromosome 11 Resulting in Male Infertility Associated with Defects in Microtubule Assembly and Sperm Tail Function1

SETDB1 Links the Meiotic DNA Damage Response to Sex Chromosome Silencing in Mice

Meiotic synapsis and recombination ensure correct homologous segregation and genetic diversity. Asynapsed homologs are transcriptionally inactivated by meiotic silencing, which serves a surveillance function and in males drives meiotic sex chromosome inactivation. Silencing depends on the DNA damage response (DDR) network, but how DDR proteins engage repressive chromatin marks is unknown. We identify the histone H3-lysine-9 methyltransferase SETDB1 as the bridge linking the DDR to silencing in male mice. At the onset of silencing, X chromosome H3K9 trimethylation (H3K9me3) enrichment is downstream of DDR factors. Without Setdb1, the X chromosome accrues DDR proteins but not H3K9me3. Consequently, sex chromosome remodeling and silencing fail, causing germ cell apoptosis. Our data implicate TRIM28 in linking the DDR to SETDB1 and uncover additional factors with putative meiotic XY-silencing functions. Furthermore, we show that SETDB1 imposes timely expression of meiotic and post-meiotic genes. Setdb1 thus unites the DDR network, asynapsis, and meiotic chromosome silencing.

Ggnbp2-Null Mutation in Mice Leads to Male Infertility due to a Defect at the Spermiogenesis Stage

Gametogenetin binding protein 2 (GGNBP2) is an evolutionarily conserved zinc finger protein. Although Ggnbp2-null embryos in the B6 background died because of a defective placenta, 6.8% of Ggnbp2-null mice in the B6/129 mixed background were viable and continued to adulthood. Adult Ggnbp2-null males were sterile, with smaller testes and an azoospermic phenotype, whereas mutant females were fertile. Histopathological analysis of 2-month-old Ggnbp2-null testes revealed absence of mature spermatozoa in the seminiferous tubules and epididymides and reduction of the number of spermatids. Ultrastructural analysis indicated dramatic morphological defects of developing spermatids in the Ggnbp2-null testes, including irregularly shaped acrosomes, acrosome detachment, cytoplasmic remnant, ectopic manchette, and ill-formed head shape in both elongating and elongated spermatids. However, the numbers of spermatogonia, spermatocytes, Leydig cells, and Sertoli cells in Ggnbp2-null testes did not significantly differ from the wild-type siblings. Gonadotropins, testosterone, and the blood-testis barrier were essentially unaffected. Western blot analyses showed increases in α-E-catenin, β-catenin, and N-cadherin, decreases in E-cadherin, afadin, and nectin-3, and no changes in vinculin, nectin-2, focal adhesion kinase, and integrin-β1 protein levels in Ggnbp2-null testes compared to wild-type siblings. Together, this study demonstrates that GGNBP2 is critically required for maintenance of the adhesion integrity of the adlumenal germ epithelium and is indispensable for normal spermatid transformation into mature spermatozoa in mice.

Microtubules and spermatogenesis

Microtubules are dynamic polymers of tubulin subunits that underpin many essential cellular processes, such as cell division and migration. Spermatogenesis is the process by which spermatogenic stem cells undergo mitotic and meiotic division and differentiation to produce streamlined spermatozoa capable of motility and fertilization. This review summarizes the current knowledge of microtubule-based processes in spermatogenesis. We describe the involvement of microtubule dynamics in Sertoli cell shape and function, as well as in the mitotic and meiotic division of germ cells. The roles of microtubules in sperm head shaping, via the development and function of the manchette, and in sperm flagella development are also discussed. The review brings together data from microscopy studies and genetically modified mouse models, and reveals that the regulation of microtubule dynamics is essential for male fertility.

New point mutation in Golga3 causes multiple defects in spermatogenesis

Mice with repro27 exhibit fully penetrant male-specific infertility associated with a nonsense mutation in the golgin subfamily A member 3 gene (Golga3). GOLGA3 is a Golgi complex-associated protein implicated in protein trafficking, apoptosis, positioning of the Golgi and spermatogenesis. In repro27 mutant mice, a point mutation in exon 18 of the Golga3 gene that inserts a pre-mature termination codon leads to an absence of GOLGA3 protein expression. GOLGA3 protein was undetectable in the brain, heart and liver in both mutant and control mice. Although spermatogenesis in Golga3(repro27) mutant mice appears to initiate normally, development is disrupted in late meiosis during the first wave of spermatogenesis, leading to significant germ cell loss between 15 and 18 days post-partum (dpp). Terminal Deoxynucleotidyl Transferase dUTP-mediated Nick End Labeling analysis showed elevated DNA fragmentation in meiotic germ cells by 12 dpp, suggesting apoptosis as a mechanism of germ cell loss. The few surviving post-meiotic round spermatids exhibited abnormal spermiogenesis with defects in acrosome formation, head and tail development and extensive vacuolization in the seminiferous epithelium. Analysis of epididymal spermatozoa showed significantly low sperm concentration and motility and in vitro fertilization with mutant spermatozoa was unsuccessful. Golga3(repro27) mice lack GOLGA3 protein and thus provide an in vivo tool to aid in deciphering the role of GOLGA3 in Golgi complex positioning, cargo trafficking and apoptosis signalling in male germ cells.

Genome-wide ENU mutagenesis in combination with high density SNP analysis and exome sequencing provides rapid identification of novel mouse models of developmental disease

BACKGROUND

Mice harbouring gene mutations that cause phenotypic abnormalities during organogenesis are invaluable tools for linking gene function to normal development and human disorders. To generate mouse models harbouring novel alleles that are involved in organogenesis we conducted a phenotype-driven, genome-wide mutagenesis screen in mice using the mutagen N-ethyl-N-nitrosourea (ENU).

METHODOLOGY/PRINCIPAL FINDINGS

ENU was injected into male C57BL/6 mice and the mutations transmitted through the germ-line. ENU-induced mutations were bred to homozygosity and G3 embryos screened at embryonic day (E) 13.5 and E18.5 for abnormalities in limb and craniofacial structures, skin, blood, vasculature, lungs, gut, kidneys, ureters and gonads. From 52 pedigrees screened 15 were detected with anomalies in one or more of the structures/organs screened. Using single nucleotide polymorphism (SNP)-based linkage analysis in conjunction with candidate gene or next-generation sequencing (NGS) we identified novel recessive alleles for Fras1, Ift140 and Lig1.

CONCLUSIONS/SIGNIFICANCE

In this study we have generated mouse models in which the anomalies closely mimic those seen in human disorders. The association between novel mutant alleles and phenotypes will lead to a better understanding of gene function in normal development and establish how their dysfunction causes human anomalies and disease.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Discovery of candidate disease genes in ENU-induced mouse mutants by large-scale sequencing, including a splice-site mutation in nucleoredoxin

An accurate and precisely annotated genome assembly is a fundamental requirement for functional genomic analysis. Here, the complete DNA sequence and gene annotation of mouse Chromosome 11 was used to test the efficacy of large-scale sequencing for mutation identification. We re-sequenced the 14,000 annotated exons and boundaries from over 900 genes in 41 recessive mutant mouse lines that were isolated in an N-ethyl-N-nitrosourea (ENU) mutation screen targeted to mouse Chromosome 11. Fifty-nine sequence variants were identified in 55 genes from 31 mutant lines. 39% of the lesions lie in coding sequences and create primarily missense mutations. The other 61% lie in noncoding regions, many of them in highly conserved sequences. A lesion in the perinatal lethal line l11Jus13 alters a consensus splice site of nucleoredoxin (Nxn), inserting 10 amino acids into the resulting protein. We conclude that point mutations can be accurately and sensitively recovered by large-scale sequencing, and that conserved noncoding regions should be included for disease mutation identification. Only seven of the candidate genes we report have been previously targeted by mutation in mice or rats, showing that despite ongoing efforts to functionally annotate genes in the mammalian genome, an enormous gap remains between phenotype and function. Our data show that the classical positional mapping approach of disease mutation identification can be extended to large target regions using high-throughput sequencing.

Differential testicular gene expression in seasonal fertility

Spermatogenesis is an essential precursor for successful sexual reproduction. Recently, there has been an expansion in the knowledge of the genes associated with particular stages of normal, physiological testicular development and pubertal activation. What has been lacking, however, is an understanding of those genes that are involved in specifically regulating sperm production, rather than in maturation and elaboration of the testis as an organ. By using the reversible (seasonal) fertility of the Syrian hamster as a model system, the authors sought to discover genes that are specifically involved in turning off sperm production and not involved in tissue specification and/or maturation. Using gene expression microarrays and in situ hybridization in hamsters and genetically infertile mice, the authors have identified a variety of known and novel factors involved in reversible, transcriptional, translational, and posttranslational control of testicular function, as well those involved in cell division and macromolecular metabolism. The novel genes uncovered could be potential targets for therapies against fertility disorders.

Fresh and frozen-thawed sperm quality, nuclear DNA integrity, invitro fertility, embryo development, and live-born offspring of N-ethyl-N-nitrosourea (ENU) mice

Efficient collection, freezing, reliable archiving of sperm, and re-derivation of mutant mice are essential components for large-scale mutagenesis programs in the mouse. Induced mutations (i.e. transgenes, targeted mutations, chemically induced mutations) in mice may cause inherited or temporary sterility, increase abnormal sperm values, or decrease fertility. One purpose of this study was to compare the effect(s) on fresh and frozen-thawed sperm quality, spermatozoa DNA integrity, unassisted in vitro fertility (IVF) rate, in vitro embryo development rate to blastocysts, and live-born offspring rates in non-ENU (control) animals and the F1-generation of N-ethyl-N-nitrosourea (ENU)-treated male mice (765mg/kg C57BL6/J or 600mg/kg 129S1/SvImJ total dose). The second purpose was to determine the effect(s) of parental oocyte donor strain on in vitro fertilization, in vitro embryo development to blastocysts, and live-born offspring rates using sperm and unassisted IVF to re-derive animals from non-ENU control and ENU mice. Sperm assessment parameters included progressive motility, concentration, plasma membrane integrity, membrane function integrity, acrosome integrity, and DNA integrity. There were no significant differences in fresh sperm assessment parameters, DNA integrity, unassisted in vitro fertility rate, in vitro embryo development rate to blastocysts, and live-born offspring rates between non-ENU and C3B6F1/J or B6129S1F1/J ENU mice. In addition, there were no significant differences in frozen-thawed sperm assessment parameters and DNA integrity rates for non-ENU control and ENU C3B6F1/J or B6129SF1/J mice. In vitro fertilization and in vitro embryo development to blastocysts were effected from strain genetic variability (P<0.05). However, the cryopreservation process caused an increase of DNA fragmentation in non-ENU control and ENU C3B6F1/J or B6129S1F1/J hybrid mice compared to fresh control sperm (P<0.01). Unlike the combinations of hybrid sperm and hybrid oocyte, increasing frozen-thawed sperm DNA fragmentation decreased the embryo development rate to blastocyst compared to fresh sperm when C57BL6, C3H, or 129S inbred mice were used as oocyte donors (P<0.05).

Structure of mammalian spermatozoa in respect to viability, fertility and cryopreservation

Morphological assessment of spermatozoa has a long history and it is generally accepted that specific morphologic structural deviations correlate with male sub- and infertility. Although many different and also new methods are used in semen analysis, light microscopy is still used for routine morphological evaluation. This paper gives an overview about the detailed structure of physiological mammalian spermatozoa as well as the most common morphological deviations in correlation to fertility. This should be the basis for explanation of problems resulting from semen cryopreservation. General aspects of semen cryopreservation should be regarded before to facilitate the understanding of methods and mechanisms.

Fast forward to new genes in mammalian reproduction

The study of reproductive genetics in mammals has lagged behind that of simpler and more tractable model organisms, such as D. melanogaster, C. elegans and various yeast models. Although much valuable information has been generated using these organisms, they do not model the genetic and biological complexity of mammalian reproduction. Thus, the majority of genes required for gametogenesis in mammals remain unidentified. To expand on the existing knowledge of mammalian reproductive genetics, we have carried out forward genetic screens in mice to identify infertility mutants and the underlying mutant genes. Two different approaches were used: mutagenesis of the germline in whole mice, and mutagenesis of embryonic stem cells. This was followed by two- or three-generation breeding schemes to identify pedigrees segregating infertility mutations, which were then phenotypically characterized, genetically mapped, and in some cases, positionally cloned. This whole-genome approach has generated a wide collection of mutants with defects ranging from problems with germ cell development to abnormal sperm morphology. These models have allowed us to study the genetics, as well as the physiology, of reproduction in mammals. This review focuses on describing some of the genes identified in these screens and the ongoing effort to characterize additional mutants.

Mutagenesis-generated mouse models of human infertility with abnormal sperm

BACKGROUND

The aetiology of human male fertility, with impairment of sperm number, motility and morphology (oligoasthenoteratozoospermia), has been difficult to understand, partly for lack of animal models.

METHODS

An ethylnitrosourea (ENU) mutagenesis strategy has been successful in producing heritable gene mutations with phenotypes similar to human male infertility, and here, we describe three independent ENU-induced mutations that cause a phenotype of oligoasthenoteratozoospermia in mice.

RESULTS

The loci identified by these three mutations are designated swm2, repro2 and repro3. All mutant males were characterized by low sperm concentration, poor sperm morphology and negligible motility, but the infertile males were apparently normal in other respects. Sperm from mutant males failed to fertilize oocytes in vitro. Ultrastructural analyses revealed varied abnormalities apparent in both testicular spermatids and epididymal sperm. Genetic mapping placed the swm2 gene on chromosome 7, the repro2 gene on chromosome 5 and the repro3 gene on chromosome 10.

CONCLUSION

The single-gene mutations caused complex and non-specific sperm pathologies, a point with important implications for managing cases of human male infertility. The ultimate identification of the loci for the mutations causing these phenotypes will clarify aetiology of complex syndromes of infertility with sperm abnormalities consistent with oligoasthenoteratozoospermia.

Mutagenesis as an unbiased approach to identify novel contraceptive targets

To accommodate diverse personal needs in family planning, diverse contraceptive approaches are desirable. This goal requires identification of new contraceptive targets. Phenotype-driven mutagenesis is an unbiased approach to identify novel genes and functions in reproductive processes. The ReproGenomics Program at The Jackson Laboratory is a United States National Institutes of Health resource for production, identification and distribution of mutant mouse models of infertility that can be used for identification of potential targets for contraception. The strategy of this program is whole genome, random ENU mutagenesis, coupled with a phenotype screen for breeding failure as the only phenotype. A three-generation breeding scheme selects recessive mutations affecting reproductive functions. G3 males and females that fail to reproduce by natural mating to wild-type animals undergo secondary phenotype screens to assess gonad and accessory organ histology, hormone production, gamete production and gamete function in fertilization. The genetic transmission of the infertility trait in each family is confirmed and each mutation is genetically mapped to a defined chromosome region, facilitating identification of candidate genes from sequence and expression databases. Genes essential for fertility in both males and females and acting both meiotically and post-meiotically have been identified by this strategy. Phenotypes include male infertility with normal sperm count, but failure in fertilization of oocytes. Phenotype descriptions of each mutation are posted on the program website, . These unique reproductive mutant mouse resources will lead to new discoveries in andrology (and gynecology) research, as well as reproductive medicine. Dissection of gene function in known and newly discovered reproductive pathways will expand our focus to reveal novel targets for contraception.

Mouse models for genes involved in impaired spermatogenesis

Since the introduction of molecular biology and gene ablation technologies there have been substantial advances in our understanding of how sperm are made and fertilization occurs. There have been at least 150 different models of specifically altered gene function produced that have resulted in male infertility spanning virtually all aspects of the spermatogenic, sperm maturation and fertilization processes. While each has, or potentially will reveal, novel aspects of these processes, there is still much of which we have little knowledge. The current review is by no means a comprehensive list of these mouse models, rather it gives an overview of the potential for such models which up to this point have generally been 'knockouts'; it presents alternative strategies for the production of new models and emphasizes the importance of thorough phenotypic analysis in order to extract a maximum amount of information from each model.

N-ethyl-N-nitrosourea (ENU) mutagenesis and male fertility research

Male infertility affects about 1 in 25 men in the western world. Conversely, there is an urgent requirement for additional male-based contraceptives, yet progress in both areas has been severely hampered by a lack of knowledge of the biochemistry and physiology of male reproductive function. It is only through a thorough knowledge of these processes that we can hope to insightfully regulate male reproductive function. Without doubt, mouse models will form an important foundation in any future process. In recent years, the chemical mutagen N-ethyl-N-nitrosourea (ENU) has been used widely to identify genes essential for a range of biological systems including male infertility. These studies have shown random mutagenesis is an attractive means of identifying key genes for male fertility. This technique has distinct, but complementary advantages compared to knockout technologies. Specifically, it allows the removal of researcher bias whereby only pre-conceived genes are tested for function; it produces mice with a guaranteed phenotype and allows for the production of allelic series of mice to dissect all aspects of gene function. ENU mouse mutagenesis programs will enable advances in the diagnosis and treatment of human male infertility and ultimately aid in the development of novel male-based contraceptives.

A repository of ENU mutant mouse lines and their potential for male fertility research

Many of the proteins and their encoding genes involved in spermatogenesis are unknown, making the specific diagnosis and treatment of infertility in males difficult and highlighting the importance of identifying new genes that are involved in spermatogenesis. Through genome-wide chemical mutagenesis using N-ethyl-N-nitrosourea (ENU) and a three-generation breeding scheme to isolate recessive mutations, we have identified mouse lines with a range of abnormalities relevant to human male fertility. Abnormal phenotypes included hypospermatogenesis, Sertoli cell-only (SCO) seminiferous tubules, germ-cell arrest and abnormal spermiogenesis and were accompanied, in some, with abnormal serum levels of reproductive hormones. In total, from 65 mouse lines, 14 showed a reproductive phenotype consistent with a recessive mutation. This study shows that it is feasible to use ENU mutagenesis as an effective and rapid means of generating mouse models relevant to furthering our understanding of human male infertility. Spermatozoa and genomic DNA from all mouse lines, including those with abnormal reproductive tract parameters, have been cryopreserved for the regeneration of lines as required. This repository will form a valuable resource for the identification and analysis of key regulators of multiple aspects of male fertility.

Deletion of the Parkin coregulated gene causes male sterility in the quaking(viable) mouse mutant

Quaking(viable) (qk(v)) is a recessive neurological mouse mutation with severe dysmyelination of the CNS and spermiogenesis failure. The molecular lesion in the qk(v) mutant is a deletion of approximately 1 Mb on mouse chromosome 17 that alters the expression of the qk gene in oligodendrocytes. Complementation analysis between the qk(v) mutation and qk mutant alleles generated through chemical mutagenesis showed that the male sterility is a distinctive feature of the qk(v) allele. This observation suggested that the sperm differentiation defect in qk(v) is due to the deletion of a gene(s) distinct from qk. Here, we demonstrate that the deletion of Pacrg is the cause of male sterility in the qk(v) mutant. Pacrg is the mouse homologue of the human PARKIN-coregulated gene (PACRG), which encodes for a protein whose biochemical function remains unclear. We show that Pacrg is highly expressed in the testes in both mice and humans. In addition, the expression pattern of Pacrg during spermiogenesis suggests that it plays a role in sperm differentiation. In support of this hypothesis, we show that transgenic expression of Pacrg in testes restores spermiogenesis and fertility in qk(v) males. This finding provides the first in vivo evidence, to our knowledge, for the function of Pacrg in a model organism. Immunolocalization experiments on isolated spermatozoa show that the Pacrg protein is present in mature sperm. Remarkably, the mammalian Pacrg protein shares significant sequence similarities with gene products from flagellated protozoans, suggesting that Pacrg may be necessary for proper flagellar formation in many organisms.