A new AURKC mutation causing macrozoospermia: implications for human spermatogenesis and clinical diagnosis

Genetic Causes of Qualitative Sperm Defects: A Narrative Review of Clinical Evidence

Several genes are implicated in spermatogenesis and fertility regulation, and these genes are presently being analysed in clinical practice due to their involvement in male factor infertility (MFI). However, there are still few genetic analyses that are currently recommended for use in clinical practice. In this manuscript, we reviewed the genetic causes of qualitative sperm defects. We distinguished between alterations causing reduced sperm motility (asthenozoospermia) and alterations causing changes in the typical morphology of sperm (teratozoospermia). In detail, the genetic causes of reduced sperm motility may be found in the alteration of genes associated with sperm mitochondrial DNA, mitochondrial proteins, ion transport and channels, and flagellar proteins. On the other hand, the genetic causes of changes in typical sperm morphology are related to conditions with a strong genetic basis, such as macrozoospermia, globozoospermia, and acephalic spermatozoa syndrome. We tried to distinguish alterations approved for routine clinical application from those still unsupported by adequate clinical studies. The most important aspect of the study was related to the correct identification of subjects to be tested and the correct application of genetic tests based on clear clinical data. The correct application of available genetic tests in a scenario where reduced sperm motility and changes in sperm morphology have been observed enables the delivery of a defined diagnosis and plays an important role in clinical decision-making. Finally, clarifying the genetic causes of MFI might, in future, contribute to reducing the proportion of so-called idiopathic MFI, which might indeed be defined as a subtype of MFI whose cause has not yet been revealed.

A variant in sperm-specific glycolytic enzyme enolase 4 (ENO4) causes human male infertility

BACKGROUND

Although defects in sperm morphology and physiology lead to male infertility, in many instances, the exact disruption of molecular pathways in a given patient is often unknown. The glycolytic pathway is an essential process to supply energy in sperm cell motility. Enolase 4 (ENO4) is crucial for the glycolytic process, which provides the energy for sperm cells in motility. ENO4 is located in the sperm principal piece and is essential for the motility and organization of the sperm flagellum. In the present study, we characterized a family with asthenozoospermia and abnormal sperm morphology as a result of a variant in the enolase 4 (ENO4) gene.

METHODS

Computer-assisted semen analysis, papanicolaou smear staining and scanning electron microscopy were used to examine sperm motility and morphology for semen analysis in patients. For genetic analysis, whole-exome sequencing followed by Sanger sequencing was performed.

RESULTS

Two brothers in a consanguineous family were being clinically investigated for sperm motility and morphology issues. Genetic analysis by whole-exome sequencing revealed a homozygous variant [c.293A>G, p.(Lys98Arg)] in the ENO4 gene that segregated with infertility in the family, shared by affected but not controls.

CONCLUSIONS

In view of the association of asthenozoospermia and abnormal sperm morphology in Eno4 knockout mice, we consider this to be the first report describing the involvement of ENO4 gene in human male infertility. We also explore the possible involvement of another variant in explaining other phenotypic features in this family.

Computational study of the potential impact of AURKC missense SNPs on AURKC-INCENP interaction and their correlation to macrozoospermia

Aurora Kinase C (AURKC) is considered an important element in Chromosome Passenger Complex (CPC), its interaction with Inner Centromere Protein (INCENP) plays a critical role in the establishment and the recruitment of a stable CPC during spermatogenesis. Genetic variations of AURKC gene are susceptible to impact AURKC-INCENP interaction, which may affect CPC stability and predispose male subjects to macrozoospermia. In this study, we systematically applied computational approaches using different bioinformatic tools to predict the effect of missense SNPs reported on AURKC gene, we selected the deleterious ones and we introduced their corresponding amino acid substitutions on AURKC protein structure. Then we did a protein-protein docking between AURKC variants and INCENP followed by a structural assessment of each resulting complex using PRODIGY server, Yassara view, Ligplot + and we choose the complexes of the most impactful variants for molecular dynamics (MD) simulation study. Seventeen missense SNPs of AURKC were identified as deleterious between all reported ones. All of them were located on relatively conserved positions on AURKC protein according to Consurf server. Only the four missense SNPs; E91K, D166V, D221Y and G235V were ranked as the most impactful ones and were chosen for MD simulation. D221Y and G235V were responsible for the most remarkable changes on AURKC-INCENP structural stability, therefore, they were selected as the most deleterious ones. Experimental studies are recommended to test the actual effect of these two variants and their actual impact on the morphology of sperm cells.Communicated by Ramaswamy H. Sarma.

A Case of Severe Teratozoospermia and Infertility Due to Homozygous Mutation c.144delC in the AURKC Gene

This case report focuses on a 33-year-old male patient with a history of infertility, characterized by severe micro-oligo-asthenospermia. Subsequent analysis revealed the presence of multi-headed and multi-flagellated spermatozoa, indicating a potential case of macrocephalic spermatozoa syndrome linked to a mutation in the AURKC gene. Genetic testing confirmed the presence of a pathogenic mutation, c.144delC, in a homozygous state in the AURKC gene. The AURKC gene is known to play a vital role in meiosis during sperm production, and its mutation can lead to abnormalities in sperm morphology and function, resulting in conditions like macrozoospermia and male infertility. Additionally, the patient was diagnosed with a grade III varicocele on the left testicle, which further contributed to his infertility. Varicoceles are associated with decreased sperm production and quality, making them one of the common reversible causes of male infertility. This case highlights the significance of comprehensive diagnostic approaches, including spermogram, ultrasonography, and genetic testing, in managing male infertility cases. It also emphasizes the intricate interplay between genetic mutations and physical conditions in the manifestation of male infertility. Further research is warranted to elucidate the mechanisms underlying AURKC-related sperm abnormalities and to develop effective therapeutic interventions. Moreover, a deeper understanding of such genetic factors may aid in the development of genetic counseling strategies for couples experiencing infertility.

Biallelic variants in KCTD19 associated with male factor infertility and oligoasthenoteratozoospermia

STUDY QUESTION

Can whole-exome sequencing (WES) reveal new genetic factors responsible for male infertility characterized by oligozoospermia?

SUMMARY ANSWER

We identified biallelic missense variants in the Potassium Channel Tetramerization Domain Containing 19 gene (KCTD19) and confirmed it to be a novel pathogenic gene for male infertility.

WHAT IS KNOWN ALREADY

KCTD19 is a key transcriptional regulator that plays an indispensable role in male fertility by regulating meiotic progression. Kctd19 gene-disrupted male mice exhibit infertility due to meiotic arrest.

STUDY DESIGN, SIZE, DURATION

We recruited a cohort of 536 individuals with idiopathic oligozoospermia from 2014 to 2022 and focused on five infertile males from three unrelated families. Semen analysis data and ICSI outcomes were collected. WES and homozygosity mapping were performed to identify potential pathogenic variants. The pathogenicity of the identified variants was investigated in silico and in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Male patients diagnosed with primary infertility were recruited from the Reproductive and Genetic Hospital of CITIC-Xiangya. Genomic DNA extracted from affected individuals was used for WES and Sanger sequencing. Sperm phenotype, sperm nuclear maturity, chromosome aneuploidy, and sperm ultrastructure were assessed using hematoxylin and eosin staining and toluidine blue staining, FISH and transmission electron microscopy. The functional effects of the identified variants in HEK293T cells were investigated via western blotting and immunofluorescence.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified three homozygous missense variants (NM_001100915, c.G628A:p.E210K, c.C893T:p.P298L, and c.G2309A:p.G770D) in KCTD19 in five infertile males from three unrelated families. Abnormal morphology of the sperm heads with immature nuclei and/or nuclear aneuploidy were frequently observed in individuals with biallelic KCTD19 variants, and ICSI was unable to rescue these deficiencies. These variants reduced the abundance of KCTD19 due to increased ubiquitination and impaired its nuclear colocalization with its functional partner, zinc finger protein 541 (ZFP541), in HEK293T cells.

LIMITATIONS, REASONS FOR CAUTION

The exact pathogenic mechanism remains unclear, and warrants further studies using knock-in mice that mimic the missense mutations found in individuals with biallelic KCTD19 variants.

WIDER IMPLICATIONS OF THE FINDINGS

Our study is the first to report a likely causal relationship between KCTD19 deficiency and male infertility, confirming the critical role of KCTD19 in human reproduction. Additionally, this study provided evidence for the poor ICSI clinical outcomes in individuals with biallelic KCTD19 variants, which may guide clinical treatment strategies.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Key Research and Developmental Program of China (2022YFC2702604 to Y.-Q.T.), the National Natural Science Foundation of China (81971447 and 82171608 to Y.-Q.T., 82101961 to C.T.), a key grant from the Prevention and Treatment of Birth Defects from Hunan Province (2019SK1012 to Y.-Q.T.), a Hunan Provincial Grant for Innovative Province Construction (2019SK4012), and the China Postdoctoral Science Foundation (2022M721124 to W.W.). The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Broad phosphorylation mediated by testis-specific serine/threonine kinases contributes to spermiogenesis and male fertility

Genetic studies elucidate a link between testis-specific serine/threonine kinases (TSSKs) and male infertility in mammals, but the underlying mechanisms are unclear. Here, we identify a TSSK homolog in Drosophila, CG14305 (termed dTSSK), whose mutation impairs the histone-to-protamine transition during spermiogenesis and causes multiple phenotypic defects in nuclear shaping, DNA condensation, and flagellar organization in spermatids. Genetic analysis demonstrates that kinase catalytic activity of dTSSK, which is functionally conserved with human TSSKs, is essential for male fertility. Phosphoproteomics identify 828 phosphopeptides/449 proteins as potential substrates of dTSSK enriched primarily in microtubule-based processes, flagellar organization and mobility, and spermatid differentiation and development, suggesting that dTSSK phosphorylates various proteins to orchestrate postmeiotic spermiogenesis. Among them, the two substrates, protamine-like protein Mst77F/Ser⁹ and transition protein Mst33A/Ser²³⁷, are biochemically validated to be phosphorylated by dTSSK in vitro, and are genetically demonstrated to be involved in spermiogenesis in vivo. Collectively, our findings demonstrate that broad phosphorylation mediated by TSSKs plays an indispensable role in spermiogenesis.

A novel homozygous mutation in DNAJB13-a gene associated with the sperm axoneme-leads to teratozoospermia

PURPOSE

To evaluate the unknown genetic causes of teratozoospermia, and determine the pathogenicity of candidate variants.

METHODS

A primary infertile patient and his family members were recruited in the West China Second University Hospital of Sichuan University. Whole-exome sequencing was performed to identify causative genes in a man with teratozoospermia. Immunofluorescence staining and western blotting were applied to assess the pathogenicity of the identified variant. Intracytoplasmic sperm injection (ICSI) was used to assist fertilization for the patient with teratozoospermia.

RESULTS

We performed whole-exome sequencing (WES) and detected a novel homozygous frameshift mutation of c.335_336del [p.E112Vfs*3] in DNAJB13 on a primary infertile male patient. Intriguingly, we identified abnormal sperm morphology in this patient, with recurrent respiratory infections and chronic cough. Furthermore, we confirmed that this mutation resulted in negative effects on DNAJB13 expression in the spermatozoa of the affected individual, causing ultrastructural defects in his sperm. Remarkably, our staining revealed that DNAJB13 was expressed in the cytoplasm of primary germ cells and in the flagella of spermatids during spermiogenesis in humans and mice. Finally, we are the first group to report a favorable prognosis using ICSI for a patient carrying this DNAJB13 mutation.

CONCLUSION

Our study revealed a novel homozygous frameshift mutation of c.335_336del [p.E112Vfs*3] in DNAJB13 involved in teratozoospermia phenotype. Our study greatly expands the spectrum of limited DNAJB13 mutations, and is expected to provide a better understanding of genetic counseling diagnoses and subsequent treatment of male infertility.

Associations between infant sex and DNA methylation across umbilical cord blood, artery, and placenta samples

DNA methylation (DNAm) is vulnerable to dysregulation by environmental exposures during epigenetic reprogramming that occurs in embryogenesis. Sexual dimorphism in environmentally induced DNAm dysregulation has been identified and therefore it is important to understand sex-specific DNAm patterns. DNAm at several autosomal sites has been consistently associated with sex in cord blood and placental foetal tissues. However, there is limited research comparing sex-specific DNAm across tissues, particularly differentially methylated regions (DMRs). This study leverages DNAm data measured using the Illumina HumanMethylation450 BeadChip in cord blood (N = 179), placenta (N = 229), and umbilical artery samples (N = 229) in the PRogramming of Intergenerational Stress Mechanisms (PRISM) cohort to identify autosomal DMRs and differentially methylated positions (DMPs). A replication analyses was conducted in an independent cohort (GEO Accession GSE129841). We identified 183, 257, and 419 DMRs and 2119, 2281, and 3405 DMPs (p_Bonferroni < 0.05) in cord blood, placenta, and artery samples, respectively. Thirty-nine DMRs overlapped in all three tissues, overlapping with genes involved in spermatogenesis (NKAPL, PIWIL2 and AURKC) and X-inactivation (LRIF1). In replication analysis, 85% of DMRs overlapped with those identified in PRISM. Overall, DMRs and DMPs had higher methylation levels among females in cord blood and artery samples, but higher methylation levels among males in placenta samples. Further research is necessary to understand biological mechanisms that contribute to differences in sex-specific DNAm signatures across tissues, as well as to determine if sexual dimorphism in the epigenome impacts response to environmental stressors.

Basonuclin 1 deficiency causes testicular premature aging: BNC1 cooperates with TAF7L to regulate spermatogenesis

Basonuclin (BNC1) is expressed primarily in proliferative keratinocytes and gametogenic cells. However, its roles in spermatogenesis and testicular aging were not clear. Previously we discovered a heterozygous BNC1 truncation mutation in a premature ovarian insufficiency pedigree. In this study, we found that male mice carrying the truncation mutation exhibited progressively fertility loss and testicular premature aging. Genome-wide expression profiling and direct binding studies (by chromatin immunoprecipitation sequencing) with BNC1 in mouse testis identified several spermatogenesis-specific gene promoters targeted by BNC1 including kelch-like family member 10 (Klhl10), testis expressed 14 (Tex14), and spermatogenesis and centriole associated 1 (Spatc1). Moreover, biochemical analysis showed that BNC1 was associated with TATA-box binding protein-associated factor 7 like (TAF7L), a germ cell-specific paralogue of the transcription factor IID subunit TAF7, both in vitro and in testis, suggesting that BNC1 might directly cooperate with TAF7L to regulate spermatogenesis. The truncation mutation disabled nuclear translocation of the BNC1/TAF7L complex, thus, disturbing expression of related genes and leading to testicular premature aging. Similarly, expressions of BNC1, TAF7L, Y-box-binding protein 2 (YBX2), outer dense fiber of sperm tails 1 (ODF1), and glyceraldehyde-3-phosphate dehydrogenase, spermatogenic (GAPDHS) were significantly decreased in the testis of men with non-obstructive azoospermia. The present study adds to the understanding of the physiology of male reproductive aging and the mechanism of spermatogenic failure in infertile men.

Genetics of teratozoospermia: Back to the head

Spermatozoa are polarized cells with a head and a flagellum joined by the connecting piece. Head integrity is critical for normal sperm function, and head defects consistently lead to male infertility. Abnormalities of the sperm head are among the most severe and characteristic sperm defects. Patients presenting with a monomorphic head sperm defects such as globozoospermia or marcrozoospermia were analyzed permitting to identify several key genes for spermatogenesis such as AURKC and DPY19L2. The study of patients with other specific sperm head defects such as acephalic spermatozoa have also enabled the identification of new infertility genes such as SUN5. Here, we review the genetic causes leading to morphological defects of sperm head. Advances in the genetics of male infertility are necessary to improve the management of infertility and will pave the road towards future strategies of treatments, especially for patients with the most severe phenotype as sperm head defects.

Molecular genetics of infertility: loss-of-function mutations in humans and corresponding knockout/mutated mice

BACKGROUND

Infertility is a major issue in human reproductive health, affecting an estimated 15% of couples worldwide. Infertility can result from disorders of sex development (DSD) or from reproductive endocrine disorders (REDs) with onset in infancy, early childhood or adolescence. Male infertility, accounting for roughly half of all infertility cases, generally manifests as decreased sperm count (azoospermia or oligozoospermia), attenuated sperm motility (asthenozoospermia) or a higher proportion of morphologically abnormal sperm (teratozoospermia). Female infertility can be divided into several classical types, including, but not limited to, oocyte maturation arrest, premature ovarian insufficiency (POI), fertilization failure and early embryonic arrest. An estimated one half of infertility cases have a genetic component; however, most genetic causes of human infertility are currently uncharacterized. The advent of high-throughput sequencing technologies has greatly facilitated the identification of infertility-associated gene mutations in patients over the past 20 years.

OBJECTIVE AND RATIONALE

This review aims to conduct a narrative review of the genetic causes of human infertility. Loss-of-function mutation discoveries related to human infertility are summarized and further illustrated in tables. Corresponding knockout/mutated animal models of causative genes for infertility are also introduced.

SEARCH METHODS

A search of the PubMed database was performed to identify relevant studies published in English. The term 'mutation' was combined with a range of search terms related to the core focus of the review: infertility, DSD, REDs, azoospermia or oligozoospermia, asthenozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF), primary ciliary dyskinesia (PCD), acephalic spermatozoa syndrome (ASS), globozoospermia, teratozoospermia, acrosome, oocyte maturation arrest, POI, zona pellucida, fertilization defects and early embryonic arrest.

OUTCOMES

Our search generated ∼2000 records. Overall, 350 articles were included in the final review. For genetic investigation of human infertility, the traditional candidate gene approach is proceeding slowly, whereas high-throughput sequencing technologies in larger cohorts of individuals is identifying an increasing number of causative genes linked to human infertility. This review provides a wide panel of gene mutations in several typical forms of human infertility, including DSD, REDs, male infertility (oligozoospermia, MMAF, PCD, ASS and globozoospermia) and female infertility (oocyte maturation arrest, POI, fertilization failure and early embryonic arrest). The causative genes, their identified mutations, mutation rate, studied population and their corresponding knockout/mutated mice of non-obstructive azoospermia, MMAF, ASS, globozoospermia, oocyte maturation arrest, POI, fertilization failure and early embryonic arrest are further illustrated by tables. In this review, we suggest that (i) our current knowledge of infertility is largely obtained from knockout mouse models; (ii) larger cohorts of clinical cases with distinct clinical characteristics need to be recruited in future studies; (iii) the whole picture of genetic causes of human infertility relies on both the identification of more mutations for distinct types of infertility and the integration of known mutation information; (iv) knockout/mutated animal models are needed to show whether the phenotypes of genetically altered animals are consistent with findings in human infertile patients carrying a deleterious mutation of the homologous gene; and (v) the molecular mechanisms underlying human infertility caused by pathogenic mutations are largely unclear in most current studies.

WILDER IMPLICATIONS

It is important to use our current understanding to identify avenues and priorities for future research in the field of genetic causes of infertility as well as to apply mutation knowledge to risk prediction, genetic diagnosis and potential treatment for human infertility.

Two frequent loss-of-function mutations in Aurora Kinase C gene in Algerian infertile men with macrozoospermia

Macrozoospermia is associated with severe male infertility. To date, the only gene implicated in this phenotype is the Aurora Kinase C gene. We report in this work the genetic screening of AURKC mutations in 34 patients with macrozoospermia among 3,536 Algerian infertile men. Nineteen patients (56%) were homozygotes for the c.144delC mutation, eight (23.52%) homozygotes for the c.744C>G (p.Y248*) mutation and two (5.88%) compound heterozygotes. No AURKC mutation was identified in five patients (14.7%). Interestingly and although it is generally accepted that nearly all positive mutated AURKC patients have close to 100% large-head spermatozoa, our results showed that 11 patients with AURKC mutations (32.35%) had large-headed spermatozoa lower than 70% (7 with c.144delC and 4 with p.Y248*), and no mutation was found in 2 patients who had >70% of macrocephalic spermatozoa. Twenty ICSI attempts were performed before genetic screening resulting in 39 embryos but no pregnancy was obtained. The sequencing of AURKC exons 3 and 6 is appropriate as a first-line genetic exploration in these patients to avoid unsuccessful ICSI attempts. A percentage of large head spermatozoa beyond 25% and a percentage of multiflagellar spermatozoa beyond 10% are predictive of a positive mutation diagnosis.

Mutation in CATIP (C2orf62) causes oligoteratoasthenozoospermia by affecting actin dynamics

BACKGROUND

Oligoteratoasthenozoospermia (OTA) combines deteriorated quantity, morphology and motility of the sperm, resulting in male factor infertility.

METHODS

We used whole genome genotyping and exome sequencing to identify the mutation causing OTA in four men in a consanguineous Bedouin family. We expressed the normal and mutated proteins tagged with c-Myc at the carboxy termini by transfection with pCDNA3.1 plasmid constructs to evaluate the effects on protein stability in HEK293 cells and on the kinetics of actin repolymerisation in retinal pigment epithelium cells. Patients' sperm samples were visualised by transmission electron microscopy to determine axoneme structures and were stained with fluorescent phalloidin to visualise the fibrillar (F)-actin.

RESULTS

A homozygous missense mutation in Ciliogenesis Associated TTC17 Interacting Protein (CATIP): c. T103A, p. Phe35Ile, a gene encoding a protein important in actin organisation and ciliogenesis, was identified as the causative mutation with a LOD score of 3.25. The mutation reduces the protein stability compared with the normal protein. Furthermore, overexpression of the normal protein, but not the mutated protein, inhibits repolymerisation of actin after disruption with cytochalasin D. A high percentage of spermatozoa axonemes from patients have abnormalities, as well as disturbances in the distribution of F-actin.

CONCLUSION

This is the first report of a recessive mutation in CATIP in humans. The identified mutation may contribute to asthenozoospermia by its involvement in actin polymerisation and on the actin cytoskeleton. A mouse knockout homozygote for CATIP was reported to demonstrate male infertility as the sole phenotype.

Compound heterozygosity for novel AURKC mutations in an infertile man with macrozoospermia

Among causes of infertility, teratozoospermia is characterised by a percentage of morphologically abnormal spermatozoa >4%. Macrozoospermia, one form of monomorphic teratozoospermia, is observed in <1% of cases of male infertility and is described as approximately 100% large-headed and/or multitailed spermatozoa. This study reports that an infertile man with large-head spermatozoa presenting compound heterozygosity aurora kinase C (AURKC) mutations (c.382C>T, c.572C>T) by whole-exome sequencing. Consequently, both two novel AURKC mutations had high probability of damage-causing and conserved across species and extremely low allele frequency in the population. Flow cytometry analysis revealed a high ratio of sperm DNA fragmentation. Two intracytoplasmic sperm injection (ICSI) procedures were attempted for the patient, but all were unsuccessful. These results indicate that sequence analysis should be performed for the variants of AURKC in Chinese patients with macrozoospermia.

Mutational analysis of Aurora kinase C gene in Egyptian patients with macrozoospermia

Macrozoospermia is a rare syndrome. The key marker of the disease is a high percentage of spermatozoa with abnormal phenotypes namely enlarged head and multiple tails. The presence of at least 70% of spermatozoa with a large head is usually associated with Aurora kinase C gene (AURKC) mutations. We sought to assess AURKC as a potential genetic actor of macrozoospermia in a sample of infertile Egyptian men. We recruited 30 patients and conducted a clinical examination, semen analysis, and DNA sequencing and RFLP for AURKC. We diagnosed 17 patients with characteristic macrozoospermia and classified them into eight severe and nine mild cases. We detected genetic variants of AURKC in five patients (29.4%): Three patients with severe macrozoospermia had c.144delC mutations in exon 3 (37.5% of the severe), and two mild cases had c.1157G>A polymorphism in the 3' UTR (22.2% of the mild). A successful intracytoplasmic sperm injection (ICSI) was achieved only with a severe macrozoospermia patient without apparent AURKC mutation. The present study is the first report to link macrozoospermia and AURKC mutations in Egypt. The study recommends macrozoospermia patients to perform AURKC gene analysis and attempt ICSI, even those with a high percentage of large head spermatozoa.

Homozygous mutations in DZIP1 can induce asthenoteratospermia with severe MMAF

BACKGROUND

Asthenoteratospermia, one of the most common causes for male infertility, often presents with defective sperm heads and/or flagella. Multiple morphological abnormalities of the sperm flagella (MMAF) is one of the common clinical manifestations of asthenoteratospermia. Variants in several genes including DNAH1, CEP135, CATSPER2 and SUN5 are involved in the genetic pathogenesis of asthenoteratospermia. However, more than half of the asthenoteratospermia cases cannot be explained by the known pathogenic genes.

METHODS AND RESULTS

Two asthenoteratospermia-affected men with severe MMAF (absent flagella in >90% spermatozoa) from consanguineous families were subjected to whole-exome sequencing. The first proband had a homozygous missense mutation c.188G>A (p.Arg63Gln) of DZIP1 and the second proband had a homozygous stop-gain mutation c.690T>G (p.Tyr230*). Both of the mutations were neither detected in the human population genome data (1000 Genomes Project, Exome Aggregation Consortium) nor in our own data of a cohort of 875 Han Chinese control populations. DZIP1 encodes a DAZ (a protein deleted in azoospermia) interacting protein, which was associated with centrosomes in mammalian cells. Immunofluorescence staining of the centriolar protein Centrin1 indicated that the spermatozoa of the proband presented with abnormal centrosomes, including no concentrated centriolar dot or more than two centriolar dots. HEK293T cells transfected with two DZIP1-mutated constructs showed reduced DZIP1 level or truncated DZIP1. The Dzip1-knockout mice, generated by the CRSIPR-Cas9, revealed consistent phenotypes of severe MMAF.

CONCLUSION

Our study strongly suggests that homozygous DZIP1 mutations can induce asthenoteratospermia with severe MMAF. The deficiency of DZIP1 induces sperm centrioles dysfunction and causes the absence of flagella.

Non-syndromic monogenic male infertility

Infertility is a widespread clinical problem affecting 8-12% of couples worldwide. Of these, about 30% are diagnosed with idiopathic infertility since no causative factor is found. Overall 40-50% of cases are due to male reproductive defects. Numerical or structural chromosome abnormalities have long been associated with male infertility. Monogenic mutations have only recently been addressed in the pathogenesis of this condition. Mutations of specific genes involved in meiosis, mitosis or spermiohistogenesis result in spermatogenic failure, leading to the following anomalies: insufficient (oligozoospermia) or no (azoospermia) sperm production, limited progressive and/or total sperm motility (asthenozoospermia), altered sperm morphology (teratozoospermia), or combinations thereof. Androgen insensitivity, causing hormonal and sexual impairment in males with normal karyotype, also affects male fertility. The genetic causes of non-syndromic monogenic of male infertility are summarized in this article and a gene panel is proposed. (www.actabiomedica.it)

The Protein Phosphorylation Landscape of Mouse Spermatids during Spermiogenesis

The characteristic tadpole shape of sperm is formed from round spermatids via spermiogenesis, a process which results in dramatic morphological changes in the final stage of spermatogenesis in the testis. Protein phosphorylation, as one of the most important post-translational modifications, can regulate spermiogenesis; however, the phosphorylation events taking place during this process have not been systematically analyzed. In order to better understand the role of phosphorylation in spermiogenesis, large-scale phosphoproteome profiling is performed using IMAC and TiO₂ enrichment. In total, 13 835 phosphorylation sites, in 4196 phosphoproteins, are identified in purified mouse spermatids undergoing spermiogenesis in two biological replicates. Overall, 735 testis-specific proteins are identified to be phosphorylated, and are expressed at high levels during spermiogenesis. Gene ontology analysis shows enrichment of the identified phosphoproteins in terms of histone modification, cilium organization, centrosome and the adherens junction. Further characterization of the kinase-substrate phosphorylation network demonstrates enrichment of phosphorylation substrates related to the regulation of spermiogenesis. This global protein phosphorylation landscape of spermiogenesis shows wide phosphoregulation across a diverse range of processes during spermiogenesis and can help to further characterize the process of sperm generation. All MS data are available via ProteomeXchange with the identifier PXD011890.

New insights into the genetics of spermatogenic failure: a review of the literature

Genetic anomalies are known to affect about 15% of infertile patients with azoospermia or severe oligozoospermia. Despite a throughout diagnostic work-up, in up to the 72% of the male partners of infertile couples, no etiological factor can be found; hence, the cause of infertility remains unclear. Recently, several novel genetic causes of spermatogenic failure (SPGF) have been described. The aim of this review was to collect all the available evidence of SPGF genetics, matching data from in-vitro and animal models with those in human beings to provide a comprehensive and updated overview of the genes capable of affecting spermatogenesis. By reviewing the literature, we provided a list of 60 candidate genes for SPGF. Their investigation by Next Generation Sequencing in large cohorts of patients with apparently idiopathic infertility would provide new interesting data about their racial- and ethnic-related prevalence in infertile patients, likely raising the diagnostic yields. We propose a phenotype-based approach to identify the genes to look for.

Genetic Factors Affecting Sperm Chromatin Structure

Spermatozoa genome has unique features that make it a fascinating field of investigation: first, because, with oocyte genome, it can be transmitted generation after generation; second, because of genetic shuffling during meiosis, each spermatozoon is virtually unique in terms of genetic content, with consequences for species evolution; and finally, because its chromatin organization is very different from that of somatic cells or oocytes, as it is not based on nucleosomes but on nucleoprotamines which confer a higher order of packaging. Histone-to-protamine transition involves many actors, such as regulators of spermatid gene expression, components of the nuclear envelop, histone-modifying enzymes and readers, chaperones, histone variants, transition proteins, protamines, and certainly many more to be discovered.In this book chapter, we will present what is currently known about sperm chromatin structure and how it is established during spermiogenesis, with the aim to list the genetic factors that regulate its organization.

Whole-exome sequencing identified a novel mutation of AURKC in a Chinese family with macrozoospermia

PURPOSE

Macrozoospermia is a rare sperm morphologic abnormality associated with male infertility and is characterized by a high percentage of spermatozoa with large irregular heads. The aim of this study was to identify the genetic cause of an infertile male with macrozoospermia from a consanguineous family.

METHODS

Whole-exome sequencing (WES) was performed using peripheral blood genomic DNA from the patient and his parents.

RESULTS

WES analysis of the patient with macrozoospermia from a consanguineous family allowed the identification of a novel homozygous missense variant in the AURKC gene (c.269G>A). Bioinformatics analysis also suggested this variant a pathogenic mutation. Quantitative real-time PCR analysis showed that the mRNA level of AURKC is significantly decreased in the patient compared with his father. Moreover, no embryos were available for transfer after ICSI.

CONCLUSIONS

These results further support the important role of AURKC in male infertility and guide the practitioner in optimal decision making for patients with macrozoospermia.

Sperm macrocephaly syndrome in the ostrich Struthio camelus: morphological characteristics and implications for motility

Sperm macrocephaly syndrome (SMS) is characterised by a high percentage of spermatozoa with enlarged heads and multiple tails, and is related to infertility. Although this multiple sperm defect has been described in other mammalian species, little is known about this anomaly in birds. Morphological examination of semen from nine South African black ostriches (Struthio camelus var. domesticus) involved in an AI trial revealed the variable presence of spermatozoa with large heads and multiple tails. Ultrastructural features of the defect were similar to those reported in mammals except that the multiple tails were collectively bound within the plasmalemma. The tails were of similar length and structure to those of normal spermatozoa, and the heads were 1.6-fold longer, emphasising the uniformity of the anomaly across vertebrate species. Flow cytometry identified these cells as diploid and computer-aided sperm analysis revealed that they swim slower but straighter than normal spermatozoa, probably due to the increased drag of the large head and constrained movement of the merged multiple tails. The high incidence of this defect in one male ostrich indicates that, although rare, SMS can occur in birds and may potentially have an adverse effect on breeding programs, particularly for endangered species.

Identification and characterization of Aurora kinase B and C variants associated with maternal aneuploidy

STUDY QUESTION

Are single nucleotide variants (SNVs) in Aurora kinases B and C (AURKB, AURKC) associated with risk of aneuploid conception?

SUMMARY ANSWER

Two SNVs were found in patients with extreme aneuploid concepti rates with respect to their age; one variant, AURKC p.I79V, is benign, while another, AURKB p.L39P, is a potential gain-of-function mutant with increased efficiency in promoting chromosome alignment.

WHAT IS KNOWN ALREADY

Maternal age does not always predict aneuploidy risk, and rare gene variants can be drivers of disease. The AURKB and AURKC regulate chromosome segregation, and are associated with reproductive impairments in mouse and human.

STUDY DESIGN, SIZE, DURATION

An extreme phenotype sample selection scheme was performed for variant discovery. Ninety-six DNA samples were from young patients with higher than average embryonic aneuploidy rates and an additional 96 DNA samples were from older patients with lower than average aneuploidy rates.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Using the192 DNA samples, the coding regions of AURKB and AURKC were sequenced using next generation sequencing. To assess biological significance, we expressed complementary RNA encoding the human variants in mouse oocytes. Assays such as determining subcellular localization and assessing catalytic activity were performed to determine alterations in protein function during meiosis.

MAIN RESULTS AND THE ROLE OF CHANCE

Ten SNVs were identified using three independent variant-calling methods. Two of the SNVs (AURKB p.L39P and AURKC p.I79V) were non-synonymous and identified by at least two variant-identification methods. The variant encoding AURKC p.I79V, identified in a young woman with a higher than average rate of aneuploid embryos, showed wild-type localization pattern and catalytic activity. On the other hand, the variant encoding AURKB p.L39P, identified in an older woman with lower than average rates of aneuploid embryos, increased the protein's ability to regulate alignment of chromosomes at the metaphase plate. These experiments were repeated three independent times using 2-3 mice for each trial.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Biological significance of the human variants was assessed in an in vitro mouse oocyte model where the variants are over-expressed. Therefore, the human protein may not function identically to the mouse homolog, or the same in mouse oocytes as in human oocytes. Furthermore, supraphysiological expression levels may not accurately reflect endogenous activity. Moreover, the evaluated variants were identified in one patient each, and no trial linking the SNV to pregnancy outcomes was conducted. Finally, the patient aneuploidy rates were established by performing comprehensive chromosome screening in blastocysts, and because of the link between female gamete aneuploidy giving rise to aneuploid embryos, we evaluate the role of the variants in Meiosis I. However, it is possible that the chromosome segregation mistake arose during Meiosis II or in mitosis in the preimplantation embryo. Their implications in human female meiosis and aneuploidy risk remain to be determined.

WIDER IMPLICATIONS OF THE FINDINGS

The data provide evidence that gene variants exist in reproductively younger or advanced aged women that are predictive of the risk of producing aneuploid concepti in humans. Furthermore, a single amino acid in the N-terminus of AURKB is a gain-of-function mutant that could be protective of euploidy.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by a Research Grant from the American Society of Reproductive Medicine and support from the Charles and Johanna Busch Memorial Fund at Rutgers, the State University of NJ to K.S. and the Foundation for Embryonic Competence, Inc to N.T. The authors declare no conflicts of interest.

Human male infertility and its genetic causes

Background

Infertility affects about 15% of couples who wish to have children and half of these cases are associated with male factors. Genetic causes of azoospermia include chromosomal abnormalities, Y chromosome microdeletions, and specific mutations/deletions of several Y chromosome genes. Many researchers have analyzed genes in the AZF region on the Y chromosome; however, in 2003 the SYCP3 gene on chromosome 12 (12q23) was identified as causing azoospermia by meiotic arrest through a point mutation.

Methods

We mainly describe the SYCP3 and PLK4 genes that we have studied in our laboratory, and add comments on other genes associated with human male infertility.

Results

Up to now, The 17 genes causing male infertility by their mutation have been reported in human.

Conclusions

Infertility caused by nonobstructive azoospermia (NOA) is very important in the field of assisted reproductive technology. Even with the aid of chromosomal analysis, ultrasonography of the testis, and detailed endocrinology, only MD‐TESE can confirm the presence of immature spermatozoa in the testes. We strongly hope that these studies help clinics avoid ineffective MD‐TESE procedures.

Genetic abnormalities leading to qualitative defects of sperm morphology or function

Infertility, defined by the inability of conceiving a child after 1 year is estimated to concern approximately 50 million couples worldwide. As the male gamete is readily accessible and can be studied by a simple spermogram it is easier to subcategorize male than female infertility. Subjects with a specific sperm phenotype are more likely to have a common origin thus facilitating the search for causal factors. Male infertility is believed to be often multifactorial and caused by both genetic and extrinsic factors, but severe cases of male infertility are likely to have a predominant genetic etiology. Patients presenting with a monomorphic teratozoospermia such as globozoospermia or macrospermia with more than 85% of the spermatozoa presenting this specific abnormality have been analyzed permitting to identify several key genes for spermatogenesis such as AURKC and DPY19L2. The study of patients with other specific sperm anomalies such as severe alteration of sperm motility, in particular multiple morphological anomalies of the sperm flagella (MMAF) or sperm unability to fertilize the oocyte (oocyte activation failure syndrome) has also enable the identification of new infertility genes. Here we review the recent works describing the identification and characterization of gene defects having a direct qualitative effect on sperm morphology or function.

Is intracouple assisted reproductive technology an option for men with large-headed spermatozoa? A literature review and a decision guide proposal

Although the presence of spermatozoa with an abnormally large head is rare, it is associated with low fertility or even total infertility. We reviewed the literature on assisted reproductive technology (ART) strategies and outcomes for men with large-headed spermatozoa. We also discuss additional analyses that can usefully characterize sperm defects and help with the choice between intra-couple ART and insemination with donor sperm. Lastly, we propose a classification for cases of large-headed spermatozoa.

Mutations of the aurora kinase C gene causing macrozoospermia are the most frequent genetic cause of male infertility in Algerian men

Klinefelter syndrome and Y-chromosomal microdeletion analyses were once the only two genetic tests offered to infertile men. Analyses of aurora kinase C (AURKC) and DPY19L2 are now recommended for patients presenting macrozoospermia and globozoospermia, respectively, two rare forms of teratozoospermia particularly frequent among North African men. We carried out genetic analyses on Algerian patients, to evaluate the prevalence of these syndromes in this population and to compare it with the expected frequency of Klinefelter syndrome and Y-microdeletions. We carried out a retrospective study on 599 consecutive patients consulting for couple infertility at the assisted reproduction unit of the Ibn Rochd Clinique, Constantine, Algeria. Abnormal sperm parameters were observed in 404 men. Fourteen and seven men had typical macrozoospermia and globozoospermia profiles, respectively. Molecular diagnosis was carried out for these patients, for the AURKC and DPY19L2 genes. Eleven men with macrozoospermia had a homozygous AURKC mutation (79%), corresponding to 2.7% of all patients with abnormal spermograms. All the men with globozoospermia studied (n = 5), corresponding to 1.2% of all infertile men, presented a homozygous DPY19L2 deletion. By comparison, we would expect 1.6% of the patients in this cohort to have Klinefelter syndrome and 0.23% to have Y-microdeletion. Our findings thus indicate that AURKC mutations are more frequent than Klinefelter syndrome and constitute the leading genetic cause of infertility in North African men. Furthermore, we estimate that AURKC and DPY19L2 molecular defects are 10 and 5 times more frequent, respectively, than Y-microdeletions.

Characterization of macrozoospermia-associated AURKC mutations in a mammalian meiotic system

Aneuploidy is the leading genetic abnormality that leads to miscarriage, and it is caused by a failure of accurate chromosome segregation during gametogenesis or early embryonic divisions. Aurora kinase C (AURKC) is essential for formation of euploid sperm in humans because mutations in AURKC are correlated with macrozoospermia and these sperm are tetraploid. These mutations are currently the most frequent mutations that cause macrozoospermia and result from an inability to complete meiosis I (MI). Three of these mutations AURKC c.144delC (AURKC p.L49Wfs22), AURKC c.686G > A (AURKC p.C229Y) and AURKC c.744C > G (AURKC p.Y248*) occur in the coding region of the gene and are the focus of this study. By expressing these alleles in oocytes isolated from Aurkc^-/- mice, we show that the mutations have different effects on AURKC function during MI. AURKC p.L49Wfs22 is a loss-of-function mutant that perturbs localization of the chromosomal passenger complex (CPC), AURKC p.C229Y is a hypomorph that cannot fully support cell-cycle progression, and AURKC p.Y248* fails to localize and function with the CPC to support chromosome segregation yet retains catalytic activity in the cytoplasm. Finally, we show that these variants of AURKC cause meiotic failure and polyploidy due to a failure in AURKC-CPC function that results in metaphase chromosome misalignment. This study is the first to assess the function of mutant alleles of AURKC that affect human fertility in a mammalian meiotic system.

Macrozoospermia: screening for the homozygous c.144delC mutation in AURKC gene in infertile men and estimation of its heterozygosity frequency in the Tunisian population

PURPOSE

Macrozoospermia is a rare condition of male infertility characterized by the presence of close to 100 % large-headed multiflagellar spermatozoa. The homozygous mutation (c.144delC) in aurora kinase C gene (AURKC) has been identified as the most frequent mutation causing macrozoospermia in North African patients. The aim of this study was to evaluate the prevalence of this condition in Tunisia and estimate the frequency of c.144delC mutation among infertile and control populations.

METHODS

Sequencing c.144delC mutation was carried out in 33 macrozoospermic patients among 6652 infertile men. Minisequencing of exon3 was performed in 250 unrelated control individuals to estimate the frequency of c.144delC heterozygosity.

RESULTS

More than 80 % of macrozoospermic patients were c.144delC homozygous. The prevalence of homozygous c.144delC was 0.4 % among infertile men (27/6652). The frequency of heterozygosity was 0.4 % among controls (1/250). Surprisingly, it is five times less common than established in the general population of North Africa (2 %) or in the Moroccan population (1.7 %).

CONCLUSIONS

We show that this mutation is relatively less frequent in the Tunisian population than in other Maghrebian populations. The occurrence of homozygous mutation among infertile men can be attributed to the high rate of consanguinity and its impact on the expression of this autosomal recessive male infertility disorder rather than a high frequency of heterozygous carriers among the general population. This highlights the importance of the molecular analysis of AURKC mutations for infertile men with high percentage of large-headed multiflagellar spermatozoa in order to limit unnecessary in vitro fertilization attempts for them.

Functions of Aurora kinase C in meiosis and cancer

The mammalian genome encodes three Aurora kinase protein family members: A, B, and C. While Aurora kinase A (AURKA) and B (AURKB) are found in cells throughout the body, significant protein levels of Aurora kinase C (AURKC) are limited to cells that undergo meiosis (sperm and oocyte). Despite its discovery nearly 20 years ago, we know little about the function of AURKC compared to that of the other 2 Aurora kinases. This lack of understanding can be attributed to the high sequence homology between AURKB and AURKC preventing the use of standard approaches to understand non-overlapping and meiosis I (MI)-specific functions of the two kinases. Recent evidence has revealed distinct functions of AURKC in meiosis and may aid in our understanding of why chromosome segregation during MI often goes awry in oocytes. Many cancers aberrantly express AURKC, but because we do not fully understand AURKC function in its normal cellular context, it is difficult to predict the biological significance of this expression on the disease. Here, we consolidate and update what is known about AURKC signaling in meiotic cells to better understand why it has oncogenic potential.

Possible Role of Aurora-C in Meiosis

The meiotic generation of haploid gametes with equal contents of genetic material is important for sexual reproduction in mammals. Errors in the transmission of chromosomes during meiosis may lead to aneuploidy, which is the leading cause of miscarriage and congenital birth defects in humans. The Aurora kinases, which include Aurora-A, Aurora-B, and Aurora-C, are highly conserved serine–threonine kinases that play essential roles in centrosome function, chromosome segregation, and cytokinesis during mitosis and meiosis. While Aurora-A and Aurora-B have been extensively studied in mitosis, the role of Aurora-C in meiosis is only now starting to be revealed. For example, the perturbation of Aurora-C kinase activity by microinjection of Aurora-C-kinase-dead mutant mRNAs into mouse oocytes induced multiple defects, including chromosome misalignment, abnormal kinetochore–microtubule attachment, premature chromosome segregation, and failure of cytokinesis during meiotic division. However, the analysis of such defects is complicated by the possibility that Aurora-B may be present in mammalian germ cells. Interestingly, a homozygous mutation of Aurora-C in humans leads to the production of large-headed polyploid spermatozoa and causes male infertility, but homozygous females are fertile. Mouse studies regarding the roles of Aurora-B and Aurora-C in female meiotic divisions have yielded inconsistent results, and it has proven difficult to explain why homozygous human females have no significant clinical phenotype. In this review, we will discuss the controversial status of Aurora-B in oocytes and the possible role of Aurora-C during meiotic division.

Male infertility and its genetic causes

AIM

Infertility is a serious social problem in advanced nations, with male factor infertility accounting for approximately half of all cases of infertility. Here, we aim to discuss our laboratory results in the context of recent literature on critical genes residing on the Y chromosome or autosomes that play important roles in human spermatogenesis.

METHODS

The PubMed database was systematically searched using the following keywords: 'genetics of male factor infertility'; 'male infertility genes', 'genetics of spermatogenesis' to retrieve information for this review.

RESULTS

Striking progress has recently been made in the elucidation of mechanisms of spermatogenesis using knockout mouse models. This information has, in many cases, not been directly translatable to humans. Nevertheless, mutations in several critical genes have been shown to cause male infertility. We discuss here the contribution to male factor infertility of a number of genes identified in the azoospermia factor (AZF) region on the Y chromosome, as well as the autosomally located genes: SYKP3, KLHL10, AURKC and SPATA16.

CONCLUSIONS

Non-obstructive azoospermia is the most severe form of azoospermia. However, the presence of spermatozoa can only be confirmed through procedures, which may prove to be unnecessary. Elucidation of the genes underlying male factor infertility, and thereby a better understanding of the mechanisms that cause it, will result in more tailored, evidence-based decisions in treatment of patients.

Teratozoospermia: spotlight on the main genetic actors in the human

BACKGROUND

Male infertility affects >20 million men worldwide and represents a major health concern. Although multifactorial, male infertility has a strong genetic basis which has so far not been extensively studied. Recent studies of consanguineous families and of small cohorts of phenotypically homogeneous patients have however allowed the identification of a number of autosomal recessive causes of teratozoospermia. Homozygous mutations of aurora kinase C (AURKC) were first described to be responsible for most cases of macrozoospermia. Other genes defects have later been identified in spermatogenesis associated 16 (SPATA16) and dpy-19-like 2 (DPY19L2) in patients with globozoospermia and more recently in dynein, axonemal, heavy chain 1 (DNAH1) in a heterogeneous group of patients presenting with flagellar abnormalities previously described as dysplasia of the fibrous sheath or short/stump tail syndromes, which we propose to call multiple morphological abnormalities of the flagella (MMAF).

METHODS

A comprehensive review of the scientific literature available in PubMed/Medline was conducted for studies on human genetics, experimental models and physiopathology related to teratozoospermia in particular globozoospermia, large headed spermatozoa and flagellar abnormalities. The search included all articles with an English abstract available online before September 2014.

RESULTS

Molecular studies of numerous unrelated patients with globozoospermia and large-headed spermatozoa confirmed that mutations in DPY19L2 and AURKC are mainly responsible for their respective pathological phenotype. In globozoospermia, the deletion of the totality of the DPY19L2 gene represents ∼ 81% of the pathological alleles but point mutations affecting the protein function have also been described. In macrozoospermia only two recurrent mutations were identified in AURKC, accounting for almost all the pathological alleles, raising the possibility of a putative positive selection of heterozygous individuals. The recent identification of DNAH1 mutations in a proportion of patients with MMAF is promising but emphasizes that this phenotype is genetically heterogeneous. Moreover, the identification of mutations in a dynein strengthens the emerging point of view that MMAF may be a phenotypic variation of the classical forms of primary ciliary dyskinesia. Based on data from human and animal models, the MMAF phenotype seems to be favored by defects directly or indirectly affecting the central pair of axonemal microtubules of the sperm flagella.

CONCLUSIONS

The studies described here provide valuable information regarding the genetic and molecular defects causing infertility, to improve our understanding of the physiopathology of teratozoospermia while giving a detailed characterization of specific features of spermatogenesis. Furthermore, these findings have a significant influence on the diagnostic strategy for teratozoospermic patients allowing the clinician to provide the patient with informed genetic counseling, to adopt the best course of treatment and to develop personalized medicine directly targeting the defective gene products.

Genetic aspects of monomorphic teratozoospermia: a review

Teratozoospermia is characterized by the presence of spermatozoa with abnormal morphology over 85 % in sperm. When all the spermatozoa display a unique abnormality, teratozoospermia is said to be monomorphic. Two forms of monomorphic teratozoospermia, representing less than 1 % of male infertility, are recognized: macrozoospermia (also called macrocephalic sperm head syndrome) and globozoospermia (also called round-headed sperm syndrome). Macrozoospermia is defined as the presence of a very high percentage of spermatozoa with enlarged head and multiple flagella. Meiotic segregation studies in 30 males revealed that over 90 % of spermatozoa were aneuploid, mainly diploid. Sperm DNA fragmentation studies performed in a few patients showed an increase in DNA fragmentation index compared to fertile men. Four mutations in the AURKC gene, a key player in meiosis and more particularly in spermatogenesis, have been found to be responsible for macrozoospermia. Globozoospermia is characterized by round-headed spermatozoa with an absent acrosome, an aberrant nuclear membrane and midpiece defects. The rate of aneuploidy of various chromosomes in spermatozoa from 26 globozoospermic men was slightly increased compared to fertile men. However, this increase was of the same order as that commonly found in infertile men with altered sperm parameters. The majority of the studies found that globozoospermic males had a sperm DNA fragmentation index higher than in fertile men. Mutations or deletions in three genes, SPATA16, PICK1 and DPY19L2, have been shown to be responsible for globozoospermia. Identification of the genetic causes of macrozoospermia and globozoospermia should help refine diagnosis and treatment of these patients, avoiding long and painful treatments. Elucidating the molecular causes of these defects is of utmost importance as intracytoplasmic sperm injection (ICSI) is very disappointing in these two pathologies.

Dpy19l2-deficient globozoospermic sperm display altered genome packaging and DNA damage that compromises the initiation of embryo development

We recently identified the DPY19L2 gene as the main genetic cause of human globozoospermia. Non-genetically characterized cases of globozoospermia were associated with DNA alterations, suggesting that DPY19L2-dependent globozoospermia may be associated with poor DNA quality. However the origins of such defects have not yet been characterized and the consequences on the quality of embryos generated with globozoospermic sperm remain to be determined. Using the mouse model lacking Dpy19l2, we compared several key steps of nuclear compaction. We show that the kinetics of appearance and disappearance of the histone H4 acetylation waves and of transition proteins are defective. More importantly, the nuclear invasion by protamines does not occur. As a consequence, we showed that globozoospermic sperm presented with poor sperm chromatin compaction and sperm DNA integrity breakdown. We next assessed the developmental consequences of using such faulty sperm by performing ICSI. We showed in the companion article that oocyte activation (OA) with globozoospermic sperm is very poor and due to the absence of phospholipase Cζ; therefore artificial OA (AOA) was used to bypass defective OA. Herein, we evaluated the developmental potential of embryos generated by ICSI + AOA in mice. We demonstrate that although OA was fully rescued, preimplantation development was impaired when using globozoospermic sperm. In human, a small number of embryos could be generated with sperm from DPY19L2-deleted patients in the absence of AOA and these embryos also showed a poor developmental potential. In conclusion, we show that chromatin compaction during spermiogenesis in Dpy19l2 KO mouse is defective and leads to sperm DNA damage. Most of the DNA breaks were already present when the sperm reached the epididymis, indicating that they occurred inside the testis. This result thus suggests that testicular sperm extraction in Dpy19l2-dependent globozoospermia is not recommended. These defects may largely explain the poor embryonic development of most mouse and human embryos obtained with globozoospermic sperm.

Selective disruption of aurora C kinase reveals distinct functions from aurora B kinase during meiosis in mouse oocytes

Aurora B kinase (AURKB) is the catalytic subunit of the chromosomal passenger complex (CPC), an essential regulator of chromosome segregation. In mitosis, the CPC is required to regulate kinetochore microtubule (K-MT) attachments, the spindle assembly checkpoint, and cytokinesis. Germ cells express an AURKB homolog, AURKC, which can also function in the CPC. Separation of AURKB and AURKC function during meiosis in oocytes by conventional approaches has not been successful. Therefore, the meiotic function of AURKC is still not fully understood. Here, we describe an ATP-binding-pocket-AURKC mutant, that when expressed in mouse oocytes specifically perturbs AURKC-CPC and not AURKB-CPC function. Using this mutant we show for the first time that AURKC has functions that do not overlap with AURKB. These functions include regulating localized CPC activity and regulating chromosome alignment and K-MT attachments at metaphase of meiosis I (Met I). We find that AURKC-CPC is not the sole CPC complex that regulates the spindle assembly checkpoint in meiosis, and as a result most AURKC-perturbed oocytes arrest at Met I. A small subset of oocytes do proceed through cytokinesis normally, suggesting that AURKC-CPC is not the sole CPC complex during telophase I. But, the resulting eggs are aneuploid, indicating that AURKC is a critical regulator of meiotic chromosome segregation in female gametes. Taken together, these data suggest that mammalian oocytes contain AURKC to efficiently execute meiosis I and ensure high-quality eggs necessary for sexual reproduction.

Sperm macrocephaly syndrome in a patient without AURKC mutations and with a history of recurrent miscarriage

This paper reports a case of recurrent miscarriage in a patient affected by a variant phenotype of sperm macrocephaly syndrome (SMS). SMS is usually related to specific sperm characteristics (large head, multiple tail) and homozygous mutations in the aurora kinase C gene (AURKC). However, the present case observed large-headed spermatozoa with no flagellar abnormalities and no mutations detectable by AURKC sequencing. Furthermore, the patient had repeatedly conceived by intracytoplasmic sperm injection, but pregnancy always aborted. This study performed morphological analysis (Papanicolau staining), annexin V/propidium iodide staining, sperm chromatin structure assay (SCSA), fluorescence in-situ hybridization (FISH) and transmission electron microscopy. This study observed large-headed, mono-tailed, mono-centriolar spermatozoa characterized by abnormal chromatin and swollen mitochondria. SCSA revealed a high ratio of late apoptotic cells with fairly intact amount of DNA. The FISH analysis showed 100% disomy rate. As far as is known, this is the first study to include gene sequencing, TEM, cytogenetic analysis and sperm DNA fragmentation in a case of SMS and also to report recurrent miscarriage related to this specific condition. SMS may be associated with important abnormalities of the sperm subcellular structure and with disomy even in the absence of mutations in the AURKC coding sequence. Sperm macrocephaly syndrome (SMS) is a rare condition that affects spermatozoa and is related to infertility. It is characterized by a specific phenotype of large-headed, multi-tailed spermatozoa with an abnormal chromosomal status. A very few pregnancies have been obtained so far in SMS patients by means of IVF procedures. We present a case of SMS that differs from the classical syndrome as we observed large-headed spermatozoa without tail abnormalities. The affected patient had achieved three pregnancies following IVF, but all aborted. We carried out a detailed examination of the patient's spermatozoa - morphological, cytogenetic, DNA fragmentation and ultrastructural analysis - and we observed that his spermatozoa are characterized by a large head whose texture appears apoptotic, a single tail and a midpiece whose mitochondria appear swollen. The DNA content within the spermatozoa was altered, as well as the chromosomal status, suggesting that some error must have occurred during spermatogenesis. Interestingly, the genetic sequencing of the specific gene usually related to SMS syndrome (AURKC) revealed no mutations in our patient, suggesting that other genes may be involved in determining this syndrome. As far as is known, this is the first study in which spermatozoa of a SMS patient have been observed using morphological analysis, ultrastructural analysis, cytogenetic analysis and sperm DNA fragmentation analysis together. Moreover, it is believed that this is first report of recurrent miscarriage due to this specific syndrome.

Maternally recruited Aurora C kinase is more stable than Aurora B to support mouse oocyte maturation and early development

Aurora kinases are highly conserved, essential regulators of cell division. Two Aurora kinase isoforms, A and B (AURKA and AURKB), are expressed ubiquitously in mammals, whereas a third isoform, Aurora C (AURKC), is largely restricted to germ cells. Because AURKC is very similar to AURKB, based on sequence and functional analyses, why germ cells express AURKC is unclear. We report that Aurkc(-/-) females are subfertile, and that AURKB function declines as development progresses based on increasing severity of cytokinesis failure and arrested embryonic development. Furthermore, we find that neither Aurkb nor Aurkc is expressed after the one-cell stage, and that AURKC is more stable during maturation than AURKB using fluorescently tagged reporter proteins. In addition, Aurkc mRNA is recruited during maturation. Because maturation occurs in the absence of transcription, posttranscriptional regulation of Aurkc mRNA, coupled with the greater stability of AURKC protein, provides a means to ensure sufficient Aurora kinase activity, despite loss of AURKB, to support both meiotic and early embryonic cell divisions. These findings suggest a model for the presence of AURKC in oocytes: that AURKC compensates for loss of AURKB through differences in both message recruitment and protein stability.

Reversine suppresses oral squamous cell carcinoma via cell cycle arrest and concomitantly apoptosis and autophagy

BACKGROUND

The effective therapies for oral cancer patients of stage III and IV are generally surgical excision and radiation combined with adjuvant chemotherapy using 5-Fu and Cisplatin. However, the five-year survival rate is still less than 30% in Taiwan. Therefore, evaluation of effective drugs for oral cancer treatment is an important issue. Many studies indicated that aurora kinases (A, B and C) were potential targets for cancer therapies. Reversine was proved to be a novel aurora kinases inhibitor with lower toxicity recently. In this study, the potentiality for reversine as an anticancer agent in oral squamous cell carcinoma (OSCC) was evaluated.

METHODS

Effects of reversine on cell growth, cell cycle progress, apoptosis, and autophagy were evaluated mainly by cell counting, flow cytometry, immunoblot, and immunofluorescence.

RESULTS

The results demonstrated that reversine significantly suppressed the proliferation of two OSCC cell lines (OC2 and OCSL) and markedly rendered cell cycle arrest at G2/M stage. Reversine also induced cell death via both caspase-dependent and -independent apoptosis. In addition, reversine could inhibit Akt/mTORC1 signaling pathway, accounting for its ability to induce autophagy.

CONCLUSIONS

Taken together, reversine suppresses growth of OSCC via multiple mechanisms, which may be a unique advantage for developing novel therapeutic regimens for treatment of oral cancer in the future.