Abnormal Spindle Formation Research Articles

Texas Native Plants Yield Compounds with Cytotoxic Activities against Prostate Cancer Cells.

There remains a critical need for more effective therapies for the treatment of late-stage and metastatic prostate cancers. Three Texas native plants yielded three new and three known compounds with antiproliferative and cytotoxic activities against prostate cancer cells with IC50 values in the range of 1.7-35.0 μM. A new sesquiterpene named espadalide (1), isolated from Gochnatia hypoleuca, had low micromolar potency and was highly effective in clonogenic assays. Two known bioactive germacranolides (2 and 3) were additionally isolated from G. hypoleuca. Dalea frutescens yielded two new isoprenylated chalcones, named sanjuanolide (4) and sanjoseolide (5), and the known sesquiterpenediol verbesindiol (6) was isolated from Verbesina virginica. Mechanistic studies showed that 1-4 caused G2/M accumulation and the formation of abnormal mitotic spindles. Tubulin polymerization assays revealed that 4 increased the initial rate of tubulin polymerization, but did not change total tubulin polymer levels, and 1-3 had no effects on tubulin polymerization. Despite its cytotoxic activity, compound 6 did not initiate changes in cell cycle distribution and has a mechanism of action different from the other compounds. This study demonstrates that new compounds with significant biological activities germane to unmet oncological needs can be isolated from Texas native plants.

Synthesis of indole–quinoline–oxadiazoles: their anticancer potential and computational tubulin binding studies

Small hybrid molecules with two or more structural pharmacores having different biological functions and distinct activity have gained a significant role in cancer drug development to combat various types of malignancies. The present study describes an efficient, clean and strategic synthesis of 12 new substituted quinoline–indole–oxadiazole hybrids from substituted 2-(quinolin-8-yloxy)acetohydrazides and indole-3-carboxylic acids by employing T3P® as a green catalyst. Structures of the newly synthesized compounds were established by IR, 1H NMR, 13C NMR, DEPT C-NMR and MS spectroscopic evidence, as well as CHN analysis data. All indole–quinoline–oxadiazoles were tested for their in vitro cytotoxic potential in breast adenocarcinoma (MCF7) and normal kidney (vero) cell lines using MTT assay. 8-((5-(3-(1H-indol-3-yl)propyl)-1,3,4-oxadiazol-2-yl)methoxy)quinoline (3d) exhibited a low IC50 value and a high selectivity index to MCF7 cells and also displayed a mitotic block in flow cytometric cell cycle progression analysis. Microtubule disruption can induce G2/M phase cell cycle arrest leading to abnormal mitotic spindle formation. Ligand 3d demonstrated its capability of being a probable tubulin inhibitor when docked in the colchicine domain of tubulin. New series of 8-((5-((1H-indol-3-yl)methyl)-1,3,4-oxadiazol-2-yl)methoxy)quinolines were synthesized using T3P® as a green catalyst and screened for their cytotoxic and antimitotic potential. The most active 8-((5-(3-(1H-indol-3-yl)propyl)-1,3,4-oxadiazol-2-yl)methoxy)quinoline 3d, displayed good binding interactions with the colchicine binding cavity of microtubule.

Effect of Type I Diabetes on the Proteome of Mouse Oocytes

Background: Type I diabetes is a global public health concern that affects young people of reproductive age and can damage oocytes, reducing their maturation rate and blocking embryonic development. Understanding the effects of type I diabetes on oocytes is important to facilitate the maintenance of reproductive capacity in female diabetic patients. Methods: To analyze the effects of type I diabetes on mammalian oocytes, protein profile changes in mice with streptozotocin-induced type I diabetes were investigated using proteomic tools; non-diabetic mouse oocytes were used as controls. Immunofluorescence analysis for the spindle and mitochondria of oocytes. Results: We found that type I diabetes severely disturbed the metabolic processes of mouse oocytes. We also observed significant changes in levels of histone H1, H2A/B, and H3 variants in diabetic oocytes (fold change: > 0.4 or < -0.4), with the potential to block activation of the zygotic genome and affect early embryo development. Furthermore, diabetic oocytes exhibited higher abnormal spindle formation and spatial remodeling of mitochondria than observed in the controls. Conclusion: Our results indicate that type I diabetes disrupts metabolic processes, spindle formation, mitochondria distribution and modulates epigenetic code in oocytes. Such effects could have a major impact on the reproductive dynamics of female patients with type I diabetes.

Biological Characterization of an Improved Pyrrole-Based Colchicine Site Agent Identified through Structure-Based Design.

A refined model of the colchicine site on tubulin was used to design an improved analog of the pyrrole parent compound, JG-03-14. The optimized compound, NT-7-16, was evaluated in biological assays that confirm that it has potent activities as a new colchicine site microtubule depolymerizer. NT-7-16 exhibits antiproliferative and cytotoxic activities against multiple cancer cell lines, with IC(50) values of 10-16 nM, and it is able to overcome drug resistance mediated by the expression of P-glycoprotein and the βIII isotype of tubulin. NT-7-16 initiated the concentration-dependent loss of cellular microtubules and caused the formation of abnormal mitotic spindles, leading to mitotic accumulation. The direct interaction of NT-7-16 with purified tubulin was confirmed, and it was more potent than combretastatin A-4 in these assays. Binding studies verified that NT-7-16 binds to tubulin within the colchicine site. The antitumor effects of NT-7-16 were evaluated in an MDA-MB-435 xenograft model and it had excellent activity at concentrations that were not toxic. A second compound, NT-9-21, which contains dichloro moieties in place of the 3,5-dibromo substituents of NT-7-16, had a poorer fit within the colchicine site as predicted by modeling and the Hydropathic INTeractions score. Biological evaluations showed that NT-9-21 has 10-fold lower potency than NT-7-16, confirming the modeling predictions. These studies highlight the value of the refined colchicine-site model and identify a new pyrrole-based colchicine-site agent with potent in vitro activities and promising in vivo antitumor actions.

STK405759 As a Novel Tubulin Active Agent for Multiple Myeloma Therapy

Background: Despite advances in treatment, multiple myeloma (MM) remains incurable due to development of drug resistance in the bone marrow microenvironment. Microtubules (MTs) are dynamic protein biopolymers formed through polymerization of heterodimers of α- and β-tubulins. Disruption of microtubules induces cell cycle arrest in G2-M phase and formation of abnormal mitotic spindles. MTs are also involved in many processes in interphase cells, including intracellular trafficking, cell motility and angiogenesis. The important functions of MT in the cells make them an attractive target for anti-myeloma drug discovery.Furan metotica is a novel class of anti-mitotic spindle drugs that inhibit kinetochore-microtubule binding and trigger a spindle checkpoint mediated arrest in mitosis, which frequently ends in cell death. We evaluated the activity of STK405759, a member of the furan metotica family, as a novel, potential antitubulin drug for MM treatment in preclinical models.Methods: Cytotoxic activity of STK405759 was evaluated by XTT assay. Apoptosis and cell cycle were analyzed by flow cytometry. Tubulin polymerization inhibition was evaluatedusing a biochemical cell free assay and by testingthe levels of soluble and polymerized tubulin in MM-treated cells using Western blot analysis. Efficacy and toxicity of the drug were checked in a murine MM xenograft model. Histochemistry was used to assay tumor apoptosis.Results: STK405759 had a potent cytotoxic activity against a wide variety of MM cell lines and patient-derived MM cells, regardless of their sensitivity to conventional therapy or novel agents. In contrast, the viability of normal peripheral blood mononuclear cells derived from healthy donors and MM patients was not affected. Importantly, STK405759 induced cell death of RPMI MM cells co-cultured with HS-5 bone marrow stromal cells.STK405759 inhibited tubulin polymerizationin a cell free system anddecreased the level of polymerized tubulin in MM treated cells.The STK405759 anti-tubulin activity was supported by demonstration of MM cell cycle arrest followed by activation of an apoptotic default pathway. Activation of pro-caspase-8 and poly (ADP-ribose) polymerase in the cleaved forms, as well as down-regulation of the Mcl-1 anti-apoptotic protein was detected in RPMI treated cells.Combination studies of STK405759 with bortezomib, lenalidomide or dexamethasone showed significant synergistic and additive cytotoxicity in MM cells. In vivo studies revealed decreased MM tumor burden and prolonged survival of STK405759-treated mice compared to controls. STK405759 induced apoptosis of tumors cells from treated mice.Summary/Conclusion: STK405759 is an active, microtubule-targeting agent with potent anti-myeloma activity. These results provide a rationale for further evaluation of STK405759 as monotherapy or part of combination therapy for treating patients with MM. DisclosuresNo relevant conflicts of interest to declare.

The putative oncogene CEP72 inhibits the mitotic function of BRCA1 and induces chromosomal instability.

BRCA1 is a tumor-suppressor gene associated with, but not restricted to, breast and ovarian cancer and implicated in various biological functions. During mitosis, BRCA1 and its positive regulator Chk2 are localized at centrosomes and are required for the regulation of microtubule plus end assembly, thereby ensuring faithful mitosis and numerical chromosome stability. However, the function of BRCA1 during mitosis has not been defined mechanistically. To gain insights into the mitotic role of BRCA1 in regulating microtubule assembly, we systematically identified proteins interacting with BRCA1 during mitosis and found the centrosomal protein Cep72 as a novel BRCA1-interacting protein. CEP72 is frequently upregulated in colorectal cancer tissues and overexpression of CEP72 mirrors the consequences of BRCA1 loss during mitosis. In detail, the overexpression of CEP72 causes an increase in microtubule plus end assembly, abnormal mitotic spindle formation and the induction of chromosomal instability. Moreover, we show that high levels of Cep72 counteract Chk2 as a positive regulator of BRCA1 to ensure proper mitotic microtubule assembly. Thus, CEP72 represents a putative oncogene in colorectal cancer that might negatively regulate the mitotic function of BRCA1 to ensure chromosomal stability.

TACC3 Is Important for Correct Progression of Meiosis in Bovine Oocytes.

Transforming acidic coiled-coil (TACC) proteins are key players during mitosis via stabilization of the spindle. The roles of TACCs during meiosis are however less clear. We used bovine oocytes to study the expression and function of TACC3 during meiosis. TACC3 mRNA was detected in bovine oocytes during meiosis using qRT-PCR, and while it was also expressed in cleavage stage embryos, its expression was down-regulated at the morula and blastocyst stages. Immunofluorescence was used to demonstrate that TACC3 co-localized with tubulin in the metaphase I and II spindles. However, TACC3 was not detected at anaphase or telophase of the first meiotic division. Aurora A, which is known to phosphorylate and activate TACC3 in mitotic cells, showed a similar pattern of gene expression to that of TACC3 in meiotic oocytes and preimplantation embryos. Aurora A protein was however only very transiently associated to the meiotic spindle. Pharmaceutical inhibition of Aurora A activity inhibited TACC3 phosphorylation but did not prevent TACC3 appearance in the spindle. Inhibiting Aurora A activity did however lead to abnormal meiotic spindle formation and impaired maturation of bovine oocytes. Similar results were obtained by knock-down of TACC3 expression using siRNA injection. These results suggest that TACC3 is important for stabilizing the meiotic spindle, but phosphorylation of TACC3 by Aurora A is not required for its recruitment to the meiotic spindle although phosphorylation of TACC3 by other kinases cannot be excluded.

Paclitaxel targets FOXM1 to regulate KIF20A in mitotic catastrophe and breast cancer paclitaxel resistance.

FOXM1 has been implicated in taxane resistance, but the molecular mechanism involved remains elusive. In here, we show that FOXM1 depletion can sensitize breast cancer cells and mouse embryonic fibroblasts into entering paclitaxel-induced senescence, with the loss of clonogenic ability, and the induction of senescence-associated β-galactosidase activity and flat cell morphology. We also demonstrate that FOXM1 regulates the expression of the microtubulin-associated kinesin KIF20A at the transcriptional level directly through a Forkhead response element (FHRE) in its promoter. Similar to FOXM1, KIF20A expression is downregulated by paclitaxel in the sensitive MCF-7 breast cancer cells and deregulated in the paclitaxel-resistant MCF-7TaxR cells. KIF20A depletion also renders MCF-7 and MCF-7TaxR cells more sensitive to paclitaxel-induced cellular senescence. Crucially, resembling paclitaxel treatment, silencing of FOXM1 and KIF20A similarly promotes abnormal mitotic spindle morphology and chromosome alignment, which have been shown to induce mitotic catastrophe-dependent senescence. The physiological relevance of the regulation of KIF20A by FOXM1 is further highlighted by the strong and significant correlations between FOXM1 and KIF20A expression in breast cancer patient samples. Statistical analysis reveals that both FOXM1 and KIF20A protein and mRNA expression significantly associates with poor survival, consistent with a role of FOXM1 and KIF20A in paclitaxel action and resistance. Collectively, our findings suggest that paclitaxel targets the FOXM1-KIF20A axis to drive abnormal mitotic spindle formation and mitotic catastrophe and that deregulated FOXM1 and KIF20A expression may confer paclitaxel resistance. These findings provide insights into the underlying mechanisms of paclitaxel resistance and have implications for the development of predictive biomarkers and novel chemotherapeutic strategies for paclitaxel resistance.

Fission yeast Scp3 potentially maintains microtubule orientation through bundling.

Microtubules play important roles in organelle transport, the maintenance of cell polarity and chromosome segregation and generally form bundles during these processes. The fission yeast gene scp3 + was identified as a multicopy suppressor of the cps3-81 mutant, which is hypersensitive to isopropyl N-3-chlorophenylcarbamate (CIPC), a poison that induces abnormal multipolar spindle formation in higher eukaryotes. In this study, we investigated the function of Scp3 along with the effect of CIPC in the fission yeast Schizosaccharomyces pombe. Microscopic observation revealed that treatment with CIPC, cps3-81 mutation and scp3 + gene deletion disturbed the orientation of microtubules in interphase cells. Overexpression of scp3 + suppressed the abnormal orientation of microtubules by promoting bundling. Functional analysis suggested that Scp3 functions independently from Ase1, a protein largely required for the bundling of the mitotic spindle. A strain lacking the ase1 + gene was more sensitive to CIPC, with the drug affecting the integrity of the mitotic spindle, indicating that CIPC has a mitotic target that has a role redundant with Ase1. These results suggested that multiple systems are independently involved to ensure microtubule orientation by bundling in fission yeast.

PLK4 is essential for meiotic resumption in mouse oocytes.

Polo-like kinase (PLK) 4 is a unique member of the PLK family that plays vital roles in centriole biogenesis during mitosis. The localization of PLK4 on centrioles must be precisely regulated during mitosis to ensure correct centriole duplication. However, little is known about the function of PLK4 in mammalian oocyte meiosis. We addressed this question by examining the expression and localization of PLK4 in mouse oocytes and using RNA interference and protein overexpression to investigate its function in meiosis. PLK4 expression peaked at the germinal vesicle breakdown (GVBD) stage, and the protein was localized in the cytoplasm throughout meiotic maturation. Depletion of PLK4 caused meiotic arrest at the GV stage and suppressed CYCLINB1 and CDC2 activities. Moreover, PLK4 depletion prevented the de-phosphorylation of CDC2-Tyr15 in nucleus and induced a decrease in the level of the CDC25C protein. PLK1 overexpression failed to rescue GV-stage arrest in PLK4-depleted oocytes, whereas overexpressing PLK4 resulted in normal GVBD in oocytes in which PLK1 activity was inhibited. In addition, PLK4 overexpression did not cause abnormal spindle formation or affect extrusion of the first polar body. These results illustrate the fact that PLK4 is essential for meiotic resumption but may not influence spindle formation in mouse oocytes during meiotic maturation.

Melampodium leucanthum, a source of cytotoxic sesquiterpenes with antimitotic activities.

A new tricyclic sesquiterpene, named meleucanthin (1), was isolated from an extract of the leaves and branches of Melampodium leucanthum, along with four known germacranolide sesquiterpene lactones, leucanthin-A (2), leucanthin-B (3), melampodin-A acetate (4), and 3α-hydroxyenhydrin (5). The chemical structure of 1 was elucidated by analysis of 1D and 2D NMR and mass spectrometric data. All compounds exhibited antiproliferative and cytotoxic efficacy against PC-3 and DU 145 prostate cancer cells, as well as HeLa cervical cancer cells, with IC50 values ranging from 0.18 to 9 μM. These compounds were effective in clonogenic assays and displayed high cellular persistence. They were also found to be capable of circumventing P-glycoprotein-mediated drug resistance. Mechanism of action studies showed that 4 caused an accumulation of cells in the G2/M phase of the cell cycle, and 2-5 caused the formation of abnormal mitotic spindles. These results suggest the cytotoxic effects of these germacranolides involve inhibition of mitotic spindle function, and it is likely that other mechanisms additionally contribute to cell death. These studies also demonstrate the possibility of isolating new, biologically active compounds from indigenous Texas plants.

Wnt-mediated protein stabilization ensures proper mitotic microtubule assembly and chromosome segregation.

Wnt signaling stimulates cell proliferation by promoting the G1/S transition of the cell cycle through β-catenin/TCF4-mediated gene transcription. However, Wnt signaling peaks in mitosis and contributes to the stabilization of proteins other than β-catenin, a pathway recently introduced as Wnt-dependent stabilization of proteins (Wnt/STOP). Here, we show that Wnt/STOP regulated by basal Wnt signaling during a normal cell cycle is required for proper spindle microtubule assembly and for faithful chromosome segregation during mitosis. Consequently, inhibition of basal Wnt signaling results in increased microtubule assembly rates, abnormal mitotic spindle formation and the induction of aneuploidy in human somatic cells.

Induction of the intrinsic apoptotic pathway via a new antimitotic agent in an esophageal carcinoma cell line.

Background2-Ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) is a unique, in silico-designed compound with possible anticancer properties, which were identified in our laboratory. This compound is capable of interfering with microtubule dynamics and is believed to have potential carbonic anhydrase IX inhibiting activity.In this study, it was investigated whether ESE-16 is capable of inducing apoptosis in vitro in the esophageal carcinoma SNO cell line via the intrinsic pathway at a concentration of 0.2 μM with an exposure time of 24 hours.ResultsQualitative results were obtained via light microscopy, transmission electron microscopy and confocal microscopy. Results showed hallmarks of apoptosis in the ESE-16-treated cells. In addition, data revealed an increase in the number of ESE-16-treated cells blocked in metaphase. Cell death via apoptosis in the ESE-16-treated cells was confirmed by studying the internal ultrastructure of the cells via transmission electron microscopy, while confocal microscopy revealed abnormal spindle formation and condensed chromatin in ESE-16-treated cells, thus confirming metaphase block.Quantitative results were obtained via flow cytometry and spectrophotometry. Cell death via apoptosis in ESE-16-treated cells was quantitatively confirmed by the Annexin V-FITC apoptosis detection assay. Flow cytometry and spectrophotometry revealed dissipation of mitochondrial membrane potential and an increase in superoxide levels in the ESE-16-treated cells when compared to the relevant controls. Both initiator caspase 9 and effector caspase 3 activities were increased, which demonstrates that ESE-16 causes cell death in a caspase-dependent manner.ConclusionsThis was the first in vitro study conducted to investigate the action mechanism of ESE-16 on an esophageal carcinoma cell line. The results provided valuable information on the action mechanism of this potential anticancer agent. It can be concluded that the novel in silico-designed compound exerts an anti-proliferative effect on the esophageal carcinoma SNO cell line by disrupting microtubule function resulting in metaphase block. This culminates in apoptotic cell death via the intrinsic apoptotic pathway. This research provided cellular targets warranting in vivo assessment of ESE-16’s potential as an anticancer agent.

Deubiquitination of γ-tubulin by BAP1 prevents chromosome instability in breast cancer cells.

Microtubule nucleation requires the γ-tubulin ring complex, and during the M-phase (mitosis) this complex accumulates at the centrosome to support mitotic spindle formation. The posttranslational modification of γ-tubulin through ubiquitination is vital for regulating microtubule nucleation and centrosome duplication. Blocking the BRCA1/BARD1-dependent ubiquitination of γ-tubulin causes centrosome amplification. In the current study, we identified BRCA1-associated protein-1 (BAP1) as a deubiquitination enzyme for γ-tubulin. BAP1 was downregulated in metastatic adenocarcinoma breast cell lines compared with noncancerous human breast epithelial cells. Furthermore, low expression of BAP1 was associated with reduced overall survival of patients with breast cancer. Reduced expression of BAP1 in breast cancer cell lines was associated with mitotic abnormalities. Importantly, rescue experiments including expression of full length but not the catalytic mutant of BAP1 reduced ubiquitination of γ-tubulin and prevented mitotic defects. Our study uncovers a new mechanism for BAP1 involved in deubiquitination of γ-tubulin, which is required to prevent abnormal mitotic spindle formation and genome instability.

Latexin sensitizes leukemogenic cells to gamma-irradiation-induced cell-cycle arrest and cell death through Rps3 pathway.

Leukemia is a leading cause of cancer death. Recently, the latexin (Lxn) gene was identified as a potential tumor suppressor in several types of solid tumors and lymphoma, and Lxn expression was found to be absent or downregulated in leukemic cells. Whether Lxn functions as a tumor suppressor in leukemia and what molecular and cellular mechanisms are involved are unknown. In this study, the myeloid leukemogenic FDC-P1 cell line was used as a model system and Lxn was ectopically expressed in these cells. Using the protein pull-down assay and mass spectrometry, ribosomal protein subunit 3 (Rps3) was identified as a novel Lxn binding protein. Ectopic expression of Lxn inhibited FDC-P1 growth in vitro. More surprisingly, Lxn enhanced gamma irradiation-induced DNA damages and induced cell-cycle arrest and massive necrosis, leading to depletion of FDC-P1 cells. Mechanistically, Lxn inhibited the nuclear translocation of Rps3 upon radiation, resulting in abnormal mitotic spindle formation and chromosome instability. Rps3 knockdown increased the radiation sensitivity of FDC-P1, confirming that the mechanism of action of Lxn is mediated by Rps3 pathway. Moreover, Lxn enhanced the cytotoxicity of chemotherapeutic agent, VP-16, on FDC-P1 cells. Our study suggests that Lxn itself not only suppresses leukemic cell growth but also potentiates the cytotoxic effect of radio- and chemotherapy on cancer cells. Lxn could be a novel molecular target that improves the efficacy of anti-cancer therapy.

Abstract 4545: Anticancer effects and mechanism of VR23, a novel chloroquine derivative

Abstract Chloroquine, a worldwide used drug in treatment of malaria, rheumatoid and other human diseases, has recently been focused as a potential anti-cancer drug as well as a chemo-sensitizer when given in combination with other anti-cancer drugs. In cancer treatment, chloroquine possesses a major potential therapeutic advantage in which it specifically targets cancer cells. Unfortunately, however, its anticancer activity is rather low. To further improve its efficacy and specificity in killing cancer cells, we created and characterized several chloroquine derivatives using a hybrid pharmacophore approach, which led us to identify VR23 as the most promising compound. Our in-vitro model of cancer cells shows that VR23 functions as a novel proteasome inhibitor. It also deregulates activity of cyclin E and other centrosomal proteins, resulting in induction of multiple centrosome amplification, abnormal spindle formation, uneven cytokinesis, irreversible mitotic arrests, and eventually apoptosis. These VR23-induced phenomena occur in cancer-specific manner and cause massive death in a variety of cancer cell types. The treatment of engrafted animals with VR23 (30 mg/kg) twice per week for three weeks effectively inhibits tumor growth. Interestingly, administration of VR23 following 24 hours pre-treatment with paclitaxel (20mg/kg/week) enhances paclitaxel's anti-tumor activity by 70%. Our histological data shows that VR23 causes substantial decrease in mitotic index, inhibition of tumor infiltration into surrounding tissues and remarkable reduction of tumor cell proliferation and angiogenesis. Most importantly, VR23 shows very low toxicity to vital organs (liver, spleen, kidney and lung) of non-tumor-bearing nude mice. In addition, VR23 seems to reduce paclitaxel-induced toxicity when used in combination. Taken together, VR23, our novel chloroquine derivative and newly discovered proteasome inhibitor, appears to be an effective and safe anticancer therapeutic alone or in combination with other anticancer agents. Citation Format: Hai-Yen Thi Vu, Sheetal Pundir, Raja V. Solomon, Hoyun Lee. Anticancer effects and mechanism of VR23, a novel chloroquine derivative. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4545. doi:10.1158/1538-7445.AM2014-4545

Microcephaly-Associated Protein WDR62 Regulates Neurogenesis through JNK1 in the Developing Neocortex

Mutations of WD40-repeat protein 62 (WDR62) have been identified recently to cause human MCPH (autosomal-recessive primary microcephaly), a neurodevelopmental disorder characterized by decreased brain size. However, the underlying mechanism is unclear. Here, we investigate the function of WDR62 in brain development and the pathological role of WDR62 mutations. We find that WDR62 knockdown leads to premature differentiation of neural progenitor cells (NPCs). The defect can be rescued by wild-type human WDR62, but not by the five MCPH-associated WDR62 mutants. We demonstrate that WDR62 acts upstream of JNK signaling in the control of neurogenesis. Depletion of JNK1 and WDR62 incurs very similar defects including abnormal spindle formation and mitotic division of NPCs as well as premature NPC differentiation during cortical development. Thus, our findings indicate that WDR62 is required for proper neurogenesis via JNK1 and provide an insight into the molecular mechanisms underlying MCPH pathogenesis.

168 INHIBITION OF BOVINE OOCYTE CUMULUS CELL PROGESTERONE SYNTHESIS DURING IN VITRO MATURATION AFFECTS CHROMOSOME ALIGNMENT AND SPINDLE INTEGRITY IN FERTILIZED EGGS AND EARLY EMBRYOS

We have previously demonstrated the importance of progesterone (P4) synthesis by cumulus cells during oocyte maturation in vitro (IVM) for bovine oocyte acquisition of developmental competence and subsequent embryo development (Aparicio et al. 2011 Biol. Reprod. 84). The aim of this study was to identify key processes that may be deregulated by the inhibition of P4 signalling in the cumulus–oocyte complex (COC) during IVM. To this end, good quality immature COC were placed in IVM medium [TCM-199 supplemented with 10% (vol/vol) FCS and 10 ng mL–1 epidermal growth factor] and cultured at 39°C for 22 h in a humidified atmosphere containing 5% CO2, in the presence or absence of 10 μM trilostane (which blocks P4 synthesis by inhibiting 3 β-hydroxysteroid dehydrogenase; Stegram Pharmaceuticals Ltd., Surrey, UK). Matured COC were washed and placed in 250 μL of fertilization medium (25 mM bicarbonate, 22 mM Na-lactate, 1 mM Na-pyruvate, 6 mg mL–1 fatty acid-free BSA, and 10 mg mL–1 heparin). In vitro fertilization (IVF) was performed with 250 μL of frozen–thawed semen at a final concentration of 1 × 106 spermatozoa mL–1 at 39°C under 5% CO2 during 20 h. Presumptive zygotes were denuded, washed, and transferred to 25-μL culture droplets (SOF + 5% FCS) at 39°C under 5% CO2, 90% of N2, and 5% O2 atmosphere with maximum humidity. Subsets of presumptive fertilized eggs and developing embryos were recovered at 6, 72, 120, and 192 h postinsemination (hpi) and processed for confocal whole-mount immunocytochemistry. The meiotic and mitotic spindles and chromosomes were visualised by immunofluorescent labelling of α-tubulin and 4′,6-diamindino-2-phenylindole (DAPI), respectively, and classified as normal if the chromosomes were correctly aligned or appropriately segregated, or abnormal if lagging chromosomes or abnormal chromosome segregation were observed. Samples were collected from 5 replicates (n = 50 zygotes/embryos per treatment, per timepoint) and a total of 157 spindles were observed. Logistic regression analysis was conducted to determine the probability of abnormal spindle formation. The incidence of spindle abnormality was regressed on time, treatment, and treatment by time. For all time points, there was significant reduction in the odds of abnormal spindle formation in control samples versus trilostane-treated samples (P &lt; 0.001). In conclusion, our data imply a role for P4 signalling in maintaining spindle integrity during oocyte meiotic maturation and progression through the initial mitotic divisions of early embryo development in cattle.

TFIIB co-localizes and interacts with α-tubulin during oocyte meiosis in the mouse and depletion of TFIIB causes arrest of subsequent embryo development.

TFIIB (transcription factor IIB) is a transcription factor that provides a bridge between promoter-bound TFIID and RNA polymerase II, and it is a target of various transcriptional activator proteins that stimulate the pre-initiation complex assembly. The localization and/or attachment matrix of TFIIB in the cytoplast is not well understood. This study focuses on the function of TFIIB and its interrelationship with α-tubulins in a mouse model. During oocyte maturation TFIIB distributes throughout the entire nucleus of the germinal vesicle (GV). After progression to GV breakdown (GVBD), TFIIB and α-tubulin co-localize and accumulate in the vicinity of the condensed chromosomes. During the MII stage, the TFIIB signals are more concentrated at the equatorial plate and the kinetochores. Colcemid treatment of oocytes disrupts the microtubule (MT) system, although the TFIIB signals are still present with the altered MT state. Injection of oocytes with TFIIB antibodies and siRNAs causes abnormal spindle formation and irregular chromosome alignment. These findings suggest that TFIIB dissociates from the condensed chromatids and then tightly binds to microtubules from GVBD to the MII phase. The assembly and disassembly of TFIIB may very well be associated with and driven by microtubules. TFIIB maintains its contact with the α-tubulins and its co-localization forms a unique distribution pattern. Depletion of Tf2b in oocytes results in a significant decrease in TFIIB expression, although polar body extrusion does not appear to be affected. Knockdown of Tf2b dramatically affects subsequent embryo development with more than 85% of the embryos arrested at the 2-cell stage. These arrested embryos still maintain apparently normal morphology for at least 96h without any obvious degeneration. Analysis of the effects of TFIIB in somatic cells by co-transfection of BiFC plasmids pHA-Tf2b and pFlag-Tuba1α further confirms a direct interaction between TFIIB and α-tubulins.

Kindlin-1 regulates mitotic spindle formation by interacting with integrins and Plk-1

Kindlin-1 binds to integrins and regulates integrin activation at cell adhesions. Here we report a new function of Kindlin-1 in regulating spindle assembly. We show that Kindlin-1 localizes to centrosomes, its concentration peaking during G2/M, where it associates with various pericentriolar material proteins, including Polo-like kinase 1. Short interfering RNA-mediated depletion of Kindlin-1 increases formation of abnormal mitotic spindles and decreases cellular survival. This effect is dependent not only on the ability of Kindlin-1 to bind integrins but also on Polo-like kinase 1-mediated Kindlin-1 phosphorylation. We demonstrate that a subcellular pool of phosphorylated Kindlin-1 is located exclusively at centrosomes. Our work identifies a novel cellular role for Kindlin-1 in ensuring mitotic spindle assembly and cellular survival that is controlled by phosphorylation via Polo-like kinase 1.