Expression and characterization of three Aurora kinase C splice variants found in human oocytes

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.

Novel insights into reproductive ageing and menopause from genomics

The post-reproductive phase or menopause in females is triggered by a physiological timer that depends on a threshold of follicle number in the ovary. Curiously, reproductive senescence appears to be decoupled from chronological age and is instead thought to be a function of physiological ageing. Ovarian ageing is associated with a decrease in oocyte developmental competence, attributed to a concomitant increase in meiotic errors. Although many biological hallmarks of general ageing are well characterized, the precise mechanisms underlying the programmed ageing of the female reproductive system remain elusive. In particular, the molecular pathways linking the external menopause trigger to the internal oocyte chromosome segregation machinery that controls fertility outcomes is unclear. However, recent large scale genomics studies have begun to provide insights into this process. Next-generation sequencing integrated with systems biology offers the advantage of sampling large datasets to uncover molecular pathways associated with a phenotype such as ageing. In this mini-review, we discuss findings from these studies that are crucial for advancing female reproductive senescence research. Targets identified in these studies can inform future animal models for menopause. We present three potential hypotheses for how external pathways governing ovarian ageing can influence meiotic chromosome segregation, with evidence from both animal models and molecular targets revealed from genomics studies. Although still in incipient stages, we discuss the potential of genomics studies combined with epigenetic age acceleration models for providing a predictive toolkit of biomarkers controlling menopause onset in women. We also speculate on future research directions to investigate extending female reproductive lifespan, such as comparative genomics in model systems that lack menopause. Novel genomics insights from such organisms are predicted to provide clues to preserving female fertility.

Meiotic defects in human oocytes: Potential causes and clinical implications

Meiotic defects cause abnormal chromosome segregation leading to aneuploidy in mammalian oocytes. Chromosome segregation is particularly error-prone in human oocytes, but the mechanisms behind such errors remain unclear. To explain the frequent chromosome segregation errors, recent investigations have identified multiple meiotic defects and explained how these defects occur in female meiosis. In particular, we review the causes of cohesin exhaustion, leaky spindle assembly checkpoint (SAC), inherently unstable meiotic spindle, fragmented kinetochores or centromeres, abnormal aurora kinases (AURK), and clinical genetic variants in human oocytes. We mainly focus on meiotic defects in human oocytes, but also refer to the potential defects of female meiosis in mouse models.

Using ZINC08918027 inhibitor to determine Aurora kinase-chromosomal passenger complex isoforms in mouse oocytes

Objective

Miscarriages affect 10% of women aged 25–29, and 53% of women over 45. The primary cause of miscarriage is aneuploidy that originated in eggs. The Aurora kinase family has three members that regulate chromosome segregation. Therefore, distinguishing the roles of these isoforms is important to understand aneuploidy etiology. In meiosis, Aurora kinase A (AURKA) localizes to spindle poles, where it binds TPX2. Aurora kinase C (AURKC) localizes on chromosomes, where it replaces AURKB as the primary AURK in the chromosomal passenger complex (CPC) via INCENP binding. Although AURKA compensates for CPC function in oocytes lacking AURKB/C, it is unknown whether AURKA binds INCENP in wild type mouse oocytes. ZINC08918027 (ZC) is an inhibitor that prevents the interaction between AURKB and INCENP in mitotic cells. We hypothesized that ZC would block CPC function of any AURK isoform.

Results

ZC treatment caused defects in meiotic progression and spindle building. By Western blotting and immunofluorescence, we observed that activated AURKA and AURKC levels in ZC-treated oocytes decreased compared to controls. These results suggest there is a population of AURKA-CPC in mouse oocytes. These data together suggest that INCENP-dependent AURKA and AURKC activities are needed for spindle bipolarity and meiotic progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-022-05987-4.

Genetic variations in AURORA cell cycle kinases are associated with glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most frequent type of primary astrocytomas. We examined the association between single nucleotide polymorphisms (SNPs) in Aurora kinase A (AURKA), Aurora kinase B (AURKB), Aurora kinase C (AURKC) and Polo-like kinase 1 (PLK1) mitotic checkpoint genes and GBM risk by qPCR genotyping. In silico analysis was performed to evaluate effects of polymorphic biological sequences on protein binding motifs. Chi-square and Fisher statistics revealed a significant difference in genotypes frequencies between GBM patients and controls for AURKB rs2289590 variant (p = 0.038). Association with decreased GBM risk was demonstrated for AURKB rs2289590 AC genotype (OR = 0.54; 95% CI = 0.33-0.88; p = 0.015). Furthermore, AURKC rs11084490 CG genotype was associated with lower GBM risk (OR = 0.57; 95% CI = 0.34-0.95; p = 0.031). Bioinformatic analysis of rs2289590 polymorphic region identified additional binding site for the Yin-Yang 1 (YY1) transcription factor in the presence of C allele. Our results indicated that rs2289590 in AURKB and rs11084490 in AURKC were associated with a reduced GBM risk. The present study was performed on a less numerous but ethnically homogeneous population. Hence, future investigations in larger and multiethnic groups are needed to strengthen these results.

Purging human ovarian cortex of contaminating leukaemic cells by targeting the mitotic catastrophe signalling pathway

PURPOSE

Is it possible to eliminate metastasised chronic myeloid leukaemia (CML) and acute myeloid leukaemia (AML) cells from ovarian cortex fragments by inhibition of Aurora B/C kinases (AURKB/C) without compromising ovarian tissue or follicles?

METHODS

Human ovarian cortex tissue with experimentally induced tumour foci of CML, AML and primary cells of AML patients were exposed to a 24h treatment with 1 μM GSK1070916, an AURKB/C inhibitor, to eliminate malignant cells by invoking mitotic catastrophe. After treatment, the inhibitor was removed, followed by an additional culture period of 6 days to allow any remaining tumour cells to form new foci. Ovarian tissue integrity after treatment was analysed by four different assays. Appropriate controls were included in all experiments.

RESULTS

Foci of metastasised CML and AML cells in ovarian cortex tissue were severely affected by a 24h ex vivo treatment with an AURKB/C inhibitor, leading to the formation of multi-nuclear syncytia and large-scale apoptosis. Ovarian tissue morphology and viability was not compromised by the treatment, as no significant difference was observed regarding the percentage of morphologically normal follicles, follicular viability, glucose uptake or in vitro growth of small follicles between ovarian cortex treated with 1 μM GSK1070916 and the control.

CONCLUSION

Purging of CML/AML metastases in ovarian cortex is possible by targeting the Mitotic Catastrophe Signalling Pathway using GSK1070916 without affecting the ovarian tissue. This provides a therapeutic strategy to prevent reintroduction of leukaemia and enhances safety of autotransplantation in leukaemia patients currently considered at high risk for ovarian involvement.

Meiosis interrupted: the genetics of female infertility via meiotic failure

Idiopathic or 'unexplained' infertility represents as many as 30% of infertility cases worldwide. Conception, implantation, and term delivery of developmentally healthy infants require chromosomally normal (euploid) eggs and sperm. The crux of euploid egg production is error-free meiosis. Pathologic genetic variants dysregulate meiotic processes that occur during prophase I, meiotic resumption, chromosome segregation, and in cell cycle regulation. This dysregulation can result in chromosomally abnormal (aneuploid) eggs. In turn, egg aneuploidy leads to a broad range of clinical infertility phenotypes, including primary ovarian insufficiency and early menopause, egg fertilization failure and embryonic developmental arrest, or recurrent pregnancy loss. Therefore, maternal genetic variants are emerging as infertility biomarkers, which could allow informed reproductive decision-making. Here, we select and deeply examine human genetic variants that likely cause dysregulation of critical meiotic processes in 14 female infertility-associated genes: SYCP3, SYCE1, TRIP13, PSMC3IP, DMC1, MCM8, MCM9, STAG3, PATL2, TUBB8, CEP120, AURKB, AURKC, andWEE2. We discuss the function of each gene in meiosis, explore genotype-phenotype relationships, and delineate the frequencies of infertility-associated variants.

Aneuploidy in human eggs: contributions of the meiotic spindle

Human eggs frequently contain an incorrect number of chromosomes, a condition termed aneuploidy. Aneuploidy affects ∼10-25% of eggs in women in their early 30s, and more than 50% of eggs from women over 40. Most aneuploid eggs cannot develop to term upon fertilization, making aneuploidy in eggs a leading cause of miscarriages and infertility. The cellular origins of aneuploidy in human eggs are incompletely understood. Aneuploidy arises from chromosome segregation errors during the two meiotic divisions of the oocyte, the progenitor cell of the egg. Chromosome segregation is driven by a microtubule spindle, which captures and separates the paired chromosomes during meiosis I, and sister chromatids during meiosis II. Recent studies reveal that defects in the organization of the acentrosomal meiotic spindle contribute to human egg aneuploidy. The microtubules of the human oocyte spindle are very frequently incorrectly attached to meiotic kinetochores, the multi-protein complexes on chromosomes to which microtubules bind. Multiple features of human oocyte spindles favour incorrect attachments. These include spindle instability and many age-related changes in chromosome and kinetochore architecture. Here, we review how the unusual spindle assembly mechanism in human oocytes contributes to the remarkably high levels of aneuploidy in young human eggs, and how age-related changes in chromosome and kinetochore architecture cause aneuploidy levels to rise even higher as women approach their forties.

Characterization and risk association of polymorphisms in Aurora kinases A, B and C with genetic susceptibility to gastric cancer development

BACKGROUND

Single nucleotide polymorphisms (SNPs) in genes encoding mitotic kinases could influence development and progression of gastric cancer (GC).

METHODS

Case-control study of nine SNPs in mitotic genes was conducted using qPCR. The study included 116 GC patients and 203 controls. In silico analysis was performed to evaluate the effects of polymorphisms on transcription factors binding sites.

RESULTS

The AURKA rs1047972 genotypes (CT vs. CC: OR, 1.96; 95% CI, 1.05-3.65; p = 0.033; CC + TT vs. CT: OR, 1.94; 95% CI, 1.04-3.60; p = 0.036) and rs911160 (CC vs. GG: OR, 5.56; 95% CI, 1.24-24.81; p = 0.025; GG + CG vs. CC: OR, 5.26; 95% CI, 1.19-23.22; p = 0.028), were associated with increased GC risk, whereas certain rs8173 genotypes (CG vs. CC: OR, 0.60; 95% CI, 0.36-0.99; p = 0.049; GG vs. CC: OR, 0.38; 95% CI, 0.18-0.79; p = 0.010; CC + CG vs. GG: OR, 0.49; 95% CI, 0.25-0.98; p = 0.043) were protective. Association with increased GC risk was demonstrated for AURKB rs2241909 (GG + AG vs. AA: OR, 1.61; 95% CI, 1.01-2.56; p = 0.041) and rs2289590 (AC vs. AA: OR, 2.41; 95% CI, 1.47-3.98; p = 0.001; CC vs. AA: OR, 6.77; 95% CI, 2.24-20.47; p = 0.001; AA+AC vs. CC: OR, 4.23; 95% CI, 1.44-12.40; p = 0.009). Furthermore, AURKC rs11084490 (GG + CG vs. CC: OR, 1.71; 95% CI, 1.04-2.81; p = 0.033) was associated with increased GC risk. A combined analysis of five SNPs, associated with an increased GC risk, detected polymorphism profiles where all the combinations contribute to the higher GC risk, with an OR increased 1.51-fold for the rs1047972(CT)/rs11084490(CG + GG) to 2.29-fold for the rs1047972(CT)/rs911160(CC) combinations. In silico analysis for rs911160 and rs2289590 demonstrated that different transcription factors preferentially bind to polymorphic sites, indicating that AURKA and AURKB could be regulated differently depending on the presence of particular allele.

CONCLUSIONS

Our results revealed that AURKA (rs1047972 and rs911160), AURKB (rs2241909 and rs2289590) and AURKC (rs11084490) are associated with a higher risk of GC susceptibility. Our findings also showed that the combined effect of these SNPs may influence GC risk, thus indicating the significance of assessing multiple polymorphisms, jointly. The study was conducted on a less numerous but ethnically homogeneous Bosnian population, therefore further investigations in larger and multiethnic groups and the assessment of functional impact of the results are needed to strengthen the findings.

Genetic Interactions between the Aurora Kinases Reveal New Requirements for AURKB and AURKC during Oocyte Meiosis

Errors in chromosome segregation during female meiosis I occur frequently, and aneuploid embryos account for 1/3 of all miscarriages in humans [1]. Unlike mitotic cells that require two Aurora kinase (AURK) homologs to help prevent aneuploidy (AURKA and AURKB), mammalian germ cells also require a third (AURKC) [2, 3]. AURKA is the spindle-pole-associated homolog, and AURKB/C are the chromosome-localized homologs. In mitosis, AURKB has essential roles as the catalytic subunit of the chromosomal passenger complex (CPC), regulating chromosome alignment, kinetochore-microtubule attachments, cohesion, the spindle assembly checkpoint, and cytokinesis [4, 5]. In mouse oocyte meiosis, AURKC takes over as the predominant CPC kinase [6], although the requirement for AURKB remains elusive [7]. In the absence of AURKC, AURKB compensates, making defining potential non-overlapping functions difficult [6, 8]. To investigate the role(s) of AURKB and AURKC in oocytes, we analyzed oocyte-specific Aurkb and Aurkc single- and double-knockout (KO) mice. Surprisingly, we find that double KO female mice are fertile. We demonstrate that, in the absence of AURKC, AURKA localizes to chromosomes in a CPC-dependent manner. These data suggest that AURKC prevents AURKA from localizing to chromosomes by competing for CPC binding. This competition is important for adequate spindle length to support meiosis I. We also describe a unique requirement for AURKB to negatively regulate AURKC to prevent aneuploidy. Together, our work reveals oocyte-specific roles for the AURKs in regulating each other's localization and activity. This inter-kinase regulation is critical to support wild-type levels of fecundity in female mice.

Aurora A Kinase Function at Kinetochores

One of the most important regulatory aspects of chromosome segregation is the ability of kinetochores to precisely control their attachment strength to spindle microtubules. Central to this regulation is Aurora B, a mitotic kinase that phosphorylates kinetochore substrates to promote microtubule turnover. A critical target of Aurora B is the kinetochore protein Ndc80/Hec1, which is a component of the NDC80 complex, the primary force-transducing link between kinetochores and microtubules. Although Aurora B is regarded as the "master regulator" of kinetochore-microtubule attachment, it is becoming clear that this kinase is not solely responsible for phosphorylating Hec1 and other kinetochore substrates to facilitate microtubule turnover. In particular, there is growing evidence that Aurora A kinase, whose activities at spindle poles have been extensively described, has additional roles at kinetochores in regulating the kinetochore-microtubule interface.

Using Mouse Oocytes to Assess Human Gene Function During Meiosis I

Embryonic aneuploidy is the major genetic cause of infertility in humans. Most of these events originate during female meiosis, and albeit positively correlated with maternal age, age alone is not always predictive of the risk of generating an aneuploid embryo. Therefore, gene variants might account for incorrect chromosome segregation during oogenesis. Given that access to human oocytes is limited for research purposes, a series of assays were developed to study human gene function during meiosis I using mouse oocytes. First, messenger RNA (mRNA) of the gene and gene variant of interest are microinjected into prophase I-arrested mouse oocytes. After allowing time for expression, oocytes are synchronously released into meiotic maturation to complete meiosis I. By tagging the mRNA with a sequence of a fluorescent reporter, such as green fluorescent protein (Gfp), the localization of the human protein can be assessed in addition to the phenotypic alterations. For example, gain or loss of function can be investigated by establishing experimental conditions that challenge the gene product to fix meiotic errors. Although this system is advantageous in investigating human protein function during oogenesis, adequate interpretation of results should be undertaken given that protein expression is not at endogenous levels and, unless controlled for (i.e. knocked out or down), murine homologs are also present in the system.

Regulation of chromosome segregation in oocytes and the cellular basis for female meiotic errors

BACKGROUND

Meiotic chromosome segregation in human oocytes is notoriously error-prone, especially with ageing. Such errors markedly reduce the reproductive chances of increasing numbers of women embarking on pregnancy later in life. However, understanding the basis for these errors is hampered by limited access to human oocytes.

OBJECTIVE AND RATIONALE

Important new discoveries have arisen from molecular analyses of human female recombination and aneuploidy along with high-resolution analyses of human oocyte maturation and mouse models. Here, we review these findings to provide a contemporary picture of the key players choreographing chromosome segregation in mammalian oocytes and the cellular basis for errors.

SEARCH METHODS

A search of PubMed was conducted using keywords including meiosis, oocytes, recombination, cohesion, cohesin complex, chromosome segregation, kinetochores, spindle, aneuploidy, meiotic cell cycle, spindle assembly checkpoint, anaphase-promoting complex, DNA damage, telomeres, mitochondria, female ageing and female fertility. We extracted papers focusing on mouse and human oocytes that best aligned with the themes of this review and that reported transformative and novel discoveries.

OUTCOMES

Meiosis incorporates two sequential rounds of chromosome segregation executed by a spindle whose component microtubules bind chromosomes via kinetochores. Cohesion mediated by the cohesin complex holds chromosomes together and should be resolved at the appropriate time, in a specific step-wise manner and in conjunction with meiotically programmed kinetochore behaviour. In women, the stage is set for meiotic error even before birth when female-specific crossover maturation inefficiency leads to the formation of at-risk recombination patterns. In adult life, multiple co-conspiring factors interact with at-risk crossovers to increase the likelihood of mis-segregation. Available evidence support that these factors include, but are not limited to, cohesion deterioration, uncoordinated sister kinetochore behaviour, erroneous microtubule attachments, spindle instability and structural chromosomal defects that impact centromeres and telomeres. Data from mice indicate that cohesin and centromere-specific histones are long-lived proteins in oocytes. Since these proteins are pivotal for chromosome segregation, but lack any obvious renewal pathway, their deterioration with age provides an appealing explanation for at least some of the problems in older oocytes.

WIDER IMPLICATIONS

Research in the mouse model has identified a number of candidate genes and pathways that are important for chromosome segregation in this species. However, many of these have not yet been investigated in human oocytes so it is uncertain at this stage to what extent they apply to women. The challenge for the future involves applying emerging knowledge of female meiotic molecular regulation towards improving clinical fertility management.

Single nucleotide polymorphisms rs911160 in AURKA and rs2289590 in AURKB mitotic checkpoint genes contribute to gastric cancer susceptibility

BACKGROUND

Single nucleotide polymorphisms (SNPs) in mitotic checkpoint genes could confer increased susceptibility to gastric cancer (GC). We investigated the association of Aurora kinase A (AURKA), Aurora kinase B (AURKB), Aurora kinase C (AURKC), Polo-like kinase 1 (PLK1) and Budding uninhibited by benzimidazol 3, yeast (BUB3) gene polymorphisms with GC risk.

MATERIALS AND METHODS

Genotyping of 6 SNPs in AURKA (rs911160 and rs8173), AURKB (rs2289590), AURKC (rs11084490), PLK1 (rs42873), and BUB3 (rs7897156) was performed using TaqMan genotyping assays.

RESULTS

Our study demonstrated that rs911160 (AURKA) heterozygous genotype was associated with an increased GC risk (OR = 1.50, 95% CI = 1.01-2.22, P = 0.043). Analysis of rs911160 (AURKA) showed significant association with an increased risk for intestinal type GC (OR = 1.80, 95%CI = 1.01-3.21, P = 0.040) and the risk was significantly higher in women than men (OR = 2.65, 95%CI = 1.02-6.87, P = 0.033). SNP rs2289590 in AURKB might contribute to susceptibility for the development of gastric cancer, particularly in women (OR = 2.08, 95% CI = 1.05-4.09, P = 0.032).

CONCLUSION

Our findings suggested that AURKA (rs911160) and AURKB (rs2289590) polymorphisms could affect GC risk. Further validation studies in larger and multi-ethnical populations are needed to elucidate their functional impact on the development of GC. Environ. Mol. Mutagen. 58:701-711, 2017. © 2017 Wiley Periodicals, Inc.

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.

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.

Association of the AURKA and AURKC gene polymorphisms with an increased risk of gastric cancer

Single nucleotide polymorphisms (SNPs) in mitotic checkpoint genes can contribute to susceptibility of human cancer, including gastric cancer (GC). We aimed to investigate the effects of Aurora kinase A (AURKA), Aurora kinase B (AURKB), and Aurora kinase C (AURKC) gene polymorphisms on GC risk in Slovenian population. We genotyped four SNPs in AURKA (rs2273535 and rs1047972), AURKB (rs2241909), and AURKC (rs758099) in a total of 128 GC patients and 372 healthy controls using TaqMan allelic discrimination assays to evaluate their effects on GC risk. Our results showed that genotype frequencies between cases and controls were significantly different for rs1047972 and rs758099 (P < 0.05). Our study demonstrated that AURKA rs1047972 TT and (CC + CT) genotypes were significantly associated with an increased risk of gastric cancer. Our results additionally revealed that AURKC rs758099 TT and (CC + CT) genotypes were also associated with increased GC risk. In stratified analysis, genotypes TT and (CC + CT) of AURKA rs1047972 SNP were associated with increased risk of both, intestinal and diffuse, types of GC. In addition, AURKC rs758099 TT and (CC + CT) genotypes were positively associated with increased intestinal type GC risk, but not with an increased diffuse type GC risk. Based on these results, we can conclude that AURKA rs1047972 and AURKC rs758099 polymorphisms could affect the risk of GC development. Further larger studies are needed to confirm these findings. © 2016 IUBMB Life, 68(8):634-644, 2016.

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.

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.