Plk4 and Aurora A cooperate in the initiation of acentriolar spindle assembly in mammalian oocytes. Bury L et al. (2017) Establishing the bipolar spindle in mammalian oocytes after their prolonged arrest is crucial for meiotic fidelity and subsequent development. In contrast to somatic cells, the first meiotic spindle assembles in the absence of centriole-containing centrosomes. Ran-GTP can promote microtubule nucleation near chromatin, but additional unidentified factors are postulated for the activity of multiple acentriolar microtubule organizing centers in the oocyte. We now demonstrate that partially overlapping, nonredundant functions of Aurora A and Plk4 kinases contribute to initiate acentriolar meiosis I spindle formation. Loss of microtubule nucleation after simultaneous chemical inhibition of both kinases can be significantly rescued by drug-resistant Aurora A alone. Drug-resistant Plk4 can enhance Aurora A-mediated rescue, and, accordingly, Plk4 can phosphorylate and potentiate the activity of Aurora A in vitro. Both kinases function distinctly from Ran, which amplifies microtubule growth. We conclude that Aurora A and Plk4 are rate-limiting factors contributing to microtubule growth as the acentriolar oocyte resumes meiosis.//////////////////
Aurora kinase-A regulates microtubule organizing center (MTOC) localization, chromosome dynamics, and histone-H3 phosphorylation in mouse oocytes. Ding J et al. Aurora kinases (AURKs) are conserved serine/threonine kinases, crucial in regulating cell cycle events. Mammalian oocytes express all three Aurk isoforms throughout meiosis, with AurkA being the predominant isoform. Inhibition of all AURK isoforms by pharmacological means disrupts oocyte meiosis. Therefore, AurkA short interfering RNA (siRNA) was performed to silence AurkA gene expression in mouse oocytes and to further assess the function of AurkA during meiosis by analyzing subsequent loss-of-function oocyte phenotypes. Results indicated that AurkA siRNA applied in our experiments specifically knocked down both AurkA gene and protein expression without influencing transcript levels of AurkB/AurkC and other endogenous protein expression, such as GAPDH and ERK-2. AURKA was not essential for resumption of meiosis, but it potentiated oocyte meiotic progression. Knockdown of AurkA led to a significant reduction in the number of oocytes proceeding to metaphase II (MII). AurkA siRNA resulted in abnormal spindle assembly, improper localization of microtubule organizing centers (MTOCs) and misalignment of chromosomes in metaphase I (MI) oocytes. Co-immunoprecipitations demonstrated that AURKA was physically associated with phospho-Histone H3 ser10 in meiotic oocytes. AurkA siRNA dramatically reduced Histone H3 ser10 phosphorylation, but not ser28, and resulted in a significant increase of abnormal chromosome segregation in MII oocytes. In conclusion, as a predominant isoform among Aurks in oocytes, AurkA plays critical roles in mouse oocyte meiosis by regulating spindle and chromosome dynamics. Mol. Reprod. Dev. ? 2011 Wiley-Liss, Inc.//////////
Aurora Kinase A Is Not Involved in CPEB1 Phosphorylation and cyclin B1 mRNA Polyadenylation during Meiotic Maturation of Porcine Oocytes. Komrskova P 2014 et al.
Regulation of mRNA translation by cytoplasmic polyadenylation is known to be important for oocyte maturation and further development. This process is generally controlled by phosphorylation of cytoplasmic polyadenylation element binding protein 1 (CPEB1). The aim of this study is to determine the role of Aurora kinase A in CPEB1 phosphorylation and the consequent CPEB1-dependent polyadenylation of maternal mRNAs during mammalian oocyte meiosis. For this purpose, we specifically inhibited Aurora kinase A with MLN8237 during meiotic maturation of porcine oocytes. Using poly(A)-test PCR method, we monitored the effect of Aurora kinase A inhibition on poly(A)-tail extension of long and short cyclin B1 encoding mRNAs as markers of CPEB1-dependent cytoplasmic polyadenylation. Our results show that inhibition of Aurora kinase A activity impairs neither cyclin B1 mRNA polyadenylation nor its translation and that Aurora kinase A is unlikely to be involved in CPEB1 activating phosphorylation.
Characterization of aurora-a in porcine oocytes and early embryos implies its functional roles in the regulation of meiotic maturation, fertilization and cleavage Yao LJ, et al .
Aurora-A is a serine/threonine protein kinase that plays important regulatory roles during mitotic cell cycle progression. In this study, Aurora-A expression, subcellular localization, and possible functions during porcine oocyte meiotic maturation, fertilization and early embryonic cleavage were studied by using Western blot, confocal microscopy and drug treatments. The quantity of Aurora-A protein remained stable during porcine oocyte meiotic maturation. Confocal microscopy revealed that Aurora-A distributed abundantly in the nucleus at the germinal vesicle stage. After germinal vesicle breakdown, Aurora-A concentrated around the condensed chromosomes and the metaphase I spindle, and finally, Aurora-A was associated with spindle poles during the formation of the metaphase II spindle. Aurora-A concentrated in the pronuclei in fertilized eggs. Aurora-A was not found in the spindle region when colchicine or staurosporine was used to inhibit microtubule organization, while it accumulated as several dots in the cytoplasm after taxol treatment. In conclusion, Aurora-A may be a multifunctional kinase that plays pivotal regulatory roles in microtubule assembly during porcine oocyte meiotic maturation, fertilization and early embryonic mitosis.
Aurora kinase A controls meiosis I progression in mouse oocytes. Saskova A et al. Aurora kinase A (AURKA), which is a centrosome-localized serine/threonine kinase crucial for cell cycle control, is critically involved in centrosome maturation and spindle assembly in somatic cells. Active T288 phosphorylated AURKA localizes to the centrosome in the late G(2) and also spreads to the minus ends of mitotic spindle microtubules. AURKA activates centrosomal CDC25B and recruits cyclin B1 to centrosomes. We report here functions for AURKA in meiotic maturation of mouse oocytes, which is a model system to study the G(2) to M transition. Whereas AURKA is present throughout the entire GV-stage oocyte with a clear accumulation on microtubule organizing centers (MTOC), active AURKA becomes entirely localized to MTOCs shortly before germinal vesicle breakdown. In contrast to somatic cells in which active AURKA is present at the centrosomes and minus ends of microtubules, active AURKA is mainly located on MTOCs at metaphase I (MI) in oocytes. Inhibitor studies using Roscovitine (CDK1 inhibitor), LY-294002 (PI3K inhibitor) and SH-6 (PKB inhibitor) reveal that activation of AURKA localized on MTOCs is independent on PI3K-PKB and CDK1 signaling pathways and MOTC amplification is observed in roscovitine- and SH-6-treated oocytes that fail to undergo nuclear envelope breakdown. Moreover, microinjection of Aurka mRNA into GV-stage oocytes cultured in 3-isobutyl-1-methyl xanthine (IBMX)-containing medium to prevent maturation also results in MOTC amplification in the absence of CDK1 activation. Overexpression of AURKA also leads to formation of an abnormal MI spindle, whereas RNAi-mediated reduction of AURKA interferes with resumption of meiosis and spindle assembly. Results of these experiments indicate that AURKA is a critical MTOC-associated component involved in resumption of meiosis, MTOC multiplication, proper spindle formation and the metaphase I-metaphase II transition.
Mutation name: None
type: null mutation
Comment: Aurora Kinase A Drives MTOC Biogenesis but Does Not Trigger Resumption of Meiosis in Mouse Oocytes Matured In Vivo. Solc P et al. Aurora kinase A (AURKA) is an important mitotic kinase involved in the G2/M transition, centrosome maturation and separation, and spindle formation in somatic cells. We used transgenic models that specifically over-express in mouse oocytes either wild-type (WT-AURKA) or a catalytically inactive (kinase-dead) (KD-AURKA) AURKA to gain new insights regarding the role of AURKA during oocyte maturation. AURKA activation occurs shortly after hCG administration that initiates maturation in vivo. Although AURKA activity is increased in WT-AURKA oocytes resumption of meiosis is not observed in the absence of hCG administration. Control oocytes contain 1-3 microtubule organizing centres (MTOCs; centrosome equivalent) at prophase I. At the time of germinal vesicle breakdown (GVBD), the first visible marker of resumption of meiosis, MTOC number increases. In WT-AURKA oocytes, the increase in MTOC number occurs prematurely but transiently without GVBD, whereas the increase in MTOC number does not occur in control and KD-AURKA oocytes. AURKA activation is biphasic with the initial activation not requiring CDC25B-CDK1 activity, whereas full activation, which is essential for the increase in MTOCs number, depends on CDK1 activity. AURKA activity also influences spindle length and regulates, independent of its protein kinase activity, the amount of MTOC-associated with ?-tubulin. Both WT-AURKA and KD-AURKA transgenic mice have normal fertility during first 6 months of life. These results suggest that although AURKA is not a trigger kinase for G2/M transition in mouse oocytes, it regulates MTOC number and spindle length, and independent of its protein kinase activity, ?-tubulin recruitment to MTOCs.
type: naturally occurring
Comment: Identification and characterization of Aurora Kinase B and C variants associated with maternal aneuploidy. Nguyen AL et al. (2017) Are single nucleotide variants (SNVs) in Aurora kinases B and C associated with risk of aneuploid conception? 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. Maternal age does not always predict aneuploidy risk, and rare gene variants can be drivers of disease. The Aurora kinases B and C regulate chromosome segregation, and are associated with reproductive impairments in mouse and human. An extreme phenotype sample selection scheme was performed for variant discovery. Out of 192 DNA samples, 96 are young patients with higher than average embryonic aneuploidy rates and 96 are older with lower than average aneuploidy rates. The coding regions of AURKB and AURKC were sequenced using next generation sequencing. To assess biological significance, we expressed cRNA 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. 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 3 independent times using 2-3 mice for each trial. 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, supra-physiological 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. 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. N/A. 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. The authors declare no conflicts of interest.//////////////////