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Tavernier N.,University Paris Diderot | Tavernier N.,The Lunenfeld Tanenbaum Research Institute | Labbe J.C.,University of Montreal | Pintard L.,University Paris Diderot
Experimental Cell Research | Year: 2015

A fundamental question in developmental biology is how different cell lineages acquire different cell cycle durations. With its highly stereotypical asymmetric and asynchronous cell divisions, the early Caenorhabditis elegans embryo provides an ideal system to study lineage-specific cell cycle timing regulation during development, with high spatio-temporal resolution. The first embryonic division is asymmetric and generates two blastomeres of different sizes (AB>P1) and developmental potentials that divide asynchronously, with the anterior somatic blastomere AB dividing reproducibly two minutes before the posterior germline blastomere P1. The evolutionarily conserved PAR proteins (abnormal embryonic PARtitioning of cytoplasm) regulate all of the asymmetries in the early embryo including cell cycle asynchrony between AB and P1 blastomeres. Here we discuss our current understanding and open questions on the mechanism by which the PAR proteins regulate asynchronous cell divisions in the early C. elegans embryo. © 2015 Elsevier Inc.

Tavernier N.,University Paris Diderot | Tavernier N.,The Lunenfeld Tanenbaum Research Institute | Panbianco C.,University of Geneva | Gotta M.,University of Geneva | Pintard L.,University Paris Diderot
Cell Cycle | Year: 2015

Mitosis is orchestrated by several protein kinases including Cdks, Plks and Aurora kinases. Despite considerable progress toward understanding the individual function of these protein kinases, how their activity is coordinated in space and time during mitosis is less well understood. In a recent article published in the Journal of Cell Biology, we show that CDK-1 regulates PLK-1 activity during mitosis in C. elegans embryos through multisite phosphorylation of the PLK-1 activator SPAT-1 (Aurora Borealis, Bora in human). SPAT-1 variants mutated on CDK-1 phosphorylation sites results in severe delays in mitotic entry, mimicking embryos lacking spat-1 or plk-1 function. We further show that SPAT-1 phosphorylation by CDK-1 promotes its binding to PLK-1 and stimulates PLK-1 phosphorylation on its activator T-loop by Aurora A kinase in vitro. Likewise, we find that phosphorylation of Bora by Cdk1 promotes phosphorylation of human Plk1 by Aurora A suggesting that this mechanism is conserved in humans. These results indicate that Cdk1 regulates Plk1 by boosting its kinase activity. Here we discuss these recent findings and open questions regarding the regulation of Plk1/PLK-1 by Cdk1/CDK-1 and Bora/SPAT-1. © 2015 Taylor & Francis Group, LLC.

Poli J.,Friedrich Miescher Institute for Biomedical Research | Gerhold C.-B.,Friedrich Miescher Institute for Biomedical Research | Tosi A.,Ludwig Maximilians University of Munich | Hustedt N.,Friedrich Miescher Institute for Biomedical Research | And 9 more authors.
Genes and Development | Year: 2016

Little is known about how cells ensure DNA replication in the face of RNA polymerase II (RNAPII)-mediated transcription, especially under conditions of replicative stress. Herewe present genetic and proteomic analyses from budding yeast that uncover links between the DNA replication checkpoint sensor Mec1–Ddc2 (ATR–ATRIP), the chromatin remodeling complex INO80C (INO80 complex), and the transcription complex PAF1C (PAF1 complex). We found that a subset of chromatin-bound RNAPII is degraded in a manner dependent on Mec1, INO80, and PAF1 complexes in cells exposed to hydroxyurea (HU). On HU, Mec1 triggers the efficient removal of PAF1C and RNAPII from transcribed genes near early firing origins. Failure to evict RNAPII correlates inversely with recovery from replication stress: paf1Δ cells, like ino80 and mec1 mutants, fail to restart forks efficiently after stalling. Our data reveal unexpected synergies between INO80C, Mec1, and PAF1C in the maintenance of genome integrity and suggest a mechanism of RNAPII degradation that reduces transcription–replication fork collision. © 2016 Poli et al.

Wong M.D.,Mouse Imaging Center | Maezawa Y.,The Lunenfeld Tanenbaum Research Institute | Lerch J.P.,Mouse Imaging Center | Lerch J.P.,University of Toronto | And 2 more authors.
Development (Cambridge) | Year: 2014

The International Mouse Phenotyping Consortium (IMPC) plans to phenotype 20,000 single-gene knockout mice to gain an insight into gene function. Approximately 30% of these knockout mouse lines will be embryonic or perinatal lethal. The IMPC has selected threedimensional (3D) imaging to phenotype these mouse lines at relevant stages of embryonic development in an attempt to discover the cause of lethality using detailed anatomical information. Rate of throughput is paramount as IMPC production centers have been given the ambitious task of completing this phenotyping project by 2021. Sifting through the wealth of data within high-resolution 3D mouse embryo data sets by trained human experts is infeasible at this scale. Here, we present a phenotyping pipeline that identifies statistically significant anatomical differences in the knockout, in comparison with the wild type, through a computer-automated image registration algorithm. This phenotyping pipeline consists of three analyses (intensity, deformation, and atlas based) that can detect missing anatomical structures and differences in volume of whole organs as well as on the voxel level. This phenotyping pipeline was applied to micro-CT images of two perinatal lethal mouse lines: a hypomorphic mutation of the Tcf21 gene (Tcf21-hypo) and a knockout of the Satb2 gene. With the proposed pipeline we were able to identify the majority of morphological phenotypes previously published for both the Tcf21-hypo and Satb2 mutant mouse embryos in addition to novel phenotypes. This phenotyping pipeline is an unbiased, automated method that highlights only those structural abnormalities that survive statistical scrutiny and illustrates them in a straightforward fashion. © 2014. Published by The Company of Biologists Ltd.

Mangerel J.,The Arthur and Sonia Labatt Brain Tumor Research Center | Price A.,The Arthur and Sonia Labatt Brain Tumor Research Center | Castelo-Branco P.,The Arthur and Sonia Labatt Brain Tumor Research Center | Castelo-Branco P.,University of Algarve | And 42 more authors.
Acta Neuropathologica | Year: 2014

Although telomeres are maintained in most cancers by telomerase activation, a subset of tumors utilize alternative lengthening of telomeres (ALT) to sustain self-renewal capacity. In order to study the prevalence and significance of ALT in childhood brain tumors we screened 517 pediatric brain tumors using the novel C-circle assay. We examined the association of ALT with alterations in genes found to segregate with specific histological phenotypes and with clinical outcome. ALT was detected almost exclusively in malignant tumors (p = 0.001). ALT was highly enriched in primitive neuroectodermal tumors (12 %), choroid plexus carcinomas (23 %) and high-grade gliomas (22 %). Furthermore, in contrast to adult gliomas, pediatric low grade gliomas which progressed to high-grade tumors did not exhibit the ALT phenotype. Somatic but not germline TP53 mutations were highly associated with ALT (p = 1.01 × 10−8). Of the other alterations examined, only ATRX point mutations and reduced expression were associated with the ALT phenotype (p = 0.0005). Interestingly, ALT attenuated the poor outcome conferred by TP53 mutations in specific pediatric brain tumors. Due to very poor prognosis, one year overall survival was quantified in malignant gliomas, while in children with choroid plexus carcinoma, five year overall survival was investigated. For children with TP53 mutant malignant gliomas, one year overall survival was 63 ± 12 and 23 ± 10 % for ALT positive and negative tumors, respectively (p = 0.03), while for children with TP53 mutant choroid plexus carcinomas, 5 years overall survival was 67 ± 19 and 27 ± 13 % for ALT positive and negative tumors, respectively (p = 0.07). These observations suggest that the presence of ALT is limited to a specific group of childhood brain cancers which harbor somatic TP53 mutations and may influence the outcome of these patients. Analysis of ALT may contribute to risk stratification and targeted therapies to improve outcome for these children. © 2014, Springer-Verlag Berlin Heidelberg.

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