Publications by authors named "Warif El Yakoubi"

12 Publications

  • Page 1 of 1

Kinetochore individualization in meiosis I is required for centromeric cohesin removal in meiosis II.

EMBO J 2021 Apr 1;40(7):e106797. Epub 2021 Mar 1.

Institut de Biologie Paris Seine, Sorbonne Université, Paris, France.

Partitioning of the genome in meiosis occurs through two highly specialized cell divisions, named meiosis I and meiosis II. Step-wise cohesin removal is required for chromosome segregation in meiosis I, and sister chromatid segregation in meiosis II. In meiosis I, mono-oriented sister kinetochores appear as fused together when examined by high-resolution confocal microscopy, whereas they are clearly separated in meiosis II, when attachments are bipolar. It has been proposed that bipolar tension applied by the spindle is responsible for the physical separation of sister kinetochores, removal of cohesin protection, and chromatid separation in meiosis II. We show here that this is not the case, and initial separation of sister kinetochores occurs already in anaphase I independently of bipolar spindle forces applied on sister kinetochores, in mouse oocytes. This kinetochore individualization depends on separase cleavage activity. Crucially, without kinetochore individualization in meiosis I, bivalents when present in meiosis II oocytes separate into chromosomes and not sister chromatids. This shows that whether centromeric cohesin is removed or not is determined by the kinetochore structure prior to meiosis II.
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http://dx.doi.org/10.15252/embj.2020106797DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8013791PMC
April 2021

Meiosis interrupted: the genetics of female infertility via meiotic failure.

Reproduction 2021 02;161(2):R13-R35

Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, New Jersey, USA.

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.
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http://dx.doi.org/10.1530/REP-20-0422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7855740PMC
February 2021

Exome sequencing links CEP120 mutation to maternally derived aneuploid conception risk.

Hum Reprod 2020 09;35(9):2134-2148

Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.

Study Question: What are the genetic factors that increase the risk of aneuploid egg production?

Summary Answer: A non-synonymous variant rs2303720 within centrosomal protein 120 (CEP120) disrupts female meiosis in vitro in mouse.

What Is Known Already: The production of aneuploid eggs, with an advanced maternal age as an established contributing factor, is the major cause of IVF failure, early miscarriage and developmental anomalies. The identity of maternal genetic variants contributing to egg aneuploidy irrespective of age is missing.

Study Design, Size, Duration: Patients undergoing fertility treatment (n = 166) were deidentified and selected for whole-exome sequencing.

Participants/materials, Setting, Methods: Patients self-identified their ethnic groups and their ages ranged from 22 to 49 years old. The study was performed using genomes from White, non-Hispanic patients divided into controls (97) and cases (69) according to the number of aneuploid blastocysts derived during each IVF procedure. Following a gene prioritization strategy, a mouse oocyte system was used to validate the functional significance of the discovered associated genetic variants.

Main Results And The Role Of Chance: Patients producing a high proportion of aneuploid blastocysts (considered aneuploid if they missed any of the 40 chromatids or had extra copies) were found to carry a higher mutational burden in genes functioning in cytoskeleton and microtubule pathways. Validation of the functional significance of a non-synonymous variant rs2303720 within Cep120 on mouse oocyte meiotic maturation revealed that ectopic expression of CEP120:p.Arg947His caused decreased spindle microtubule nucleation efficiency and increased incidence of aneuploidy.

Limitations, Reasons For Caution: Functional validation was performed using the mouse oocyte system. Because spindle building pathways differ between mouse and human oocytes, the defects we observed upon ectopic expression of the Cep120 variant may alter mouse oocyte meiosis differently than human oocyte meiosis. Further studies using knock-in 'humanized' mouse models and in human oocytes will be needed to translate our findings to human system. Possible functional differences of the variant between ethnic groups also need to be investigated.

Wider Implications Of The Findings: Variants in centrosomal genes appear to be important contributors to the risk of maternal aneuploidy. Functional validation of these variants will eventually allow prescreening to select patients that have better chances to benefit from preimplantation genetic testing.

Study Funding/competing Interest(s): This study was funded through R01-HD091331 to K.S. and J.X. and EMD Serono Grant for Fertility Innovation to N.R.T. N.R.T. is a shareholder and an employee of Genomic Prediction.

Trial Registration Number: N/A.
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http://dx.doi.org/10.1093/humrep/deaa148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7828473PMC
September 2020

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

Curr Biol 2018 11 25;28(21):3458-3468.e5. Epub 2018 Oct 25.

Department of Genetics, Rutgers University, 145 Bevier Road, Piscataway, NJ 08854, USA. Electronic address:

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.
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http://dx.doi.org/10.1016/j.cub.2018.08.052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6234855PMC
November 2018

Tension-Induced Error Correction and Not Kinetochore Attachment Status Activates the SAC in an Aurora-B/C-Dependent Manner in Oocytes.

Curr Biol 2018 01 21;28(1):130-139.e3. Epub 2017 Dec 21.

Sorbonne Universités, UPMC Univ. Paris 06, CNRS FRE3631, Institut de Biologie Paris Seine (IBPS), 7 Quai St. Bernard, Paris 75005, France; CNRS UMR7622, Developmental Biology Lab, 7 Quai St. Bernard, 75005 Paris, France. Electronic address:

Cell division with partitioning of the genetic material should take place only when paired chromosomes named bivalents (meiosis I) or sister chromatids (mitosis and meiosis II) are correctly attached to the bipolar spindle in a tension-generating manner. For this to happen, the spindle assembly checkpoint (SAC) checks whether unattached kinetochores are present, in which case anaphase onset is delayed to permit further establishment of attachments. Additionally, microtubules are stabilized when they are attached and under tension. In mitosis, attachments not under tension activate the so-named error correction pathway depending on Aurora B kinase substrate phosphorylation. This leads to microtubule detachments, which in turn activates the SAC [1-3]. Meiotic divisions in mammalian oocytes are highly error prone, with severe consequences for fertility and health of the offspring [4, 5]. Correct attachment of chromosomes in meiosis I leads to the generation of stretched bivalents, but-unlike mitosis-not to tension between sister kinetochores, which co-orient. Here, we set out to address whether reduction of tension applied by the spindle on bioriented bivalents activates error correction and, as a consequence, the SAC. Treatment of oocytes in late prometaphase I with Eg5 kinesin inhibitor affects spindle tension, but not attachments, as we show here using an optimized protocol for confocal imaging. After Eg5 inhibition, bivalents are correctly aligned but less stretched, and as a result, Aurora-B/C-dependent error correction with microtubule detachment takes place. This loss of attachments leads to SAC activation. Crucially, SAC activation itself does not require Aurora B/C kinase activity in oocytes.
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http://dx.doi.org/10.1016/j.cub.2017.11.049DOI Listing
January 2018

Mps1 kinase-dependent Sgo2 centromere localisation mediates cohesin protection in mouse oocyte meiosis I.

Nat Commun 2017 09 25;8(1):694. Epub 2017 Sep 25.

Sorbonne Universités, UPMC Univ. Paris 06, Institut de Biologie Paris Seine (IBPS), UMR7622, Paris, 75005, France.

A key feature of meiosis is the step-wise removal of cohesin, the protein complex holding sister chromatids together, first from arms in meiosis I and then from the centromere region in meiosis II. Centromeric cohesin is protected by Sgo2 from Separase-mediated cleavage, in order to maintain sister chromatids together until their separation in meiosis II. Failures in step-wise cohesin removal result in aneuploid gametes, preventing the generation of healthy embryos. Here, we report that kinase activities of Bub1 and Mps1 are required for Sgo2 localisation to the centromere region. Mps1 inhibitor-treated oocytes are defective in centromeric cohesin protection, whereas oocytes devoid of Bub1 kinase activity, which cannot phosphorylate H2A at T121, are not perturbed in cohesin protection as long as Mps1 is functional. Mps1 and Bub1 kinase activities localise Sgo2 in meiosis I preferentially to the centromere and pericentromere respectively, indicating that Sgo2 at the centromere is required for protection.In meiosis I centromeric cohesin is protected by Sgo2 from Separase-mediated cleavage ensuring that sister chromatids are kept together until their separation in meiosis II. Here the authors demonstrate that Bub1 and Mps1 kinase activities are required for Sgo2 localisation to the centromere region.
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http://dx.doi.org/10.1038/s41467-017-00774-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5612927PMC
September 2017

Meiotic Divisions: No Place for Gender Equality.

Adv Exp Med Biol 2017 ;1002:1-17

Sorbonne Universités, UPMC Univ Paris 06, Institut de Biologie Paris Seine (IBPS), UMR7622, Paris, 75252, France.

In multicellular organisms the fusion of two gametes with a haploid set of chromosomes leads to the formation of the zygote, the first cell of the embryo. Accurate execution of the meiotic cell division to generate a female and a male gamete is required for the generation of healthy offspring harboring the correct number of chromosomes. Unfortunately, meiosis is error prone. This has severe consequences for fertility and under certain circumstances, health of the offspring. In humans, female meiosis is extremely error prone. In this chapter we will compare male and female meiosis in humans to illustrate why and at which frequency errors occur, and describe how this affects pregnancy outcome and health of the individual. We will first introduce key notions of cell division in meiosis and how they differ from mitosis, followed by a detailed description of the events that are prone to errors during the meiotic divisions.
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http://dx.doi.org/10.1007/978-3-319-57127-0_1DOI Listing
September 2017

Direct regulation of siamois by VegT is required for axis formation in Xenopus embryo.

Int J Dev Biol 2015 ;59(10-12):443-51

Sorbonne Universités, UPMC Univ Paris 06, Institut de Biologie Paris-Seine (IBPS), UMR 7622, Laboratory of Developmental Biology, Paris, France.

The homeobox gene siamois is one of the earliest genes expressed in the Spemann organizer and plays a critical role in the formation of the dorsoventral axis. It is directly regulated by maternal Wnt signalling and functions as an essential zygotic intermediary between maternal factors and the formation of the Spemann organizer. The maternal T domain transcription factor VegT interacts with Wnt signalling and is also involved in the formation of the Spemann organizer. However, the molecular mechanism of this functional interaction is not fully understood. Here we show that VegT is required for siamois expression through direct binding to the T-box binding sites in the siamois promoter. Mutational analysis of each of the five consensus T-box binding sites suggests that the proximal site close to the transcription start site is essential for activation of siamois promoter by VegT, while individual mutation of the four distal sites has no effect. VegT and Wnt signalling also functionally interact and are mutually required for siamois expression. In particular, VegT synergizes with Tcf1, but not Tcf3 and Tcf4, to induce siamois expression, and this is independent of Tcf/Lef-binding sites or the proximal T-box binding site in the siamois promoter. We further extend previous observations by showing that VegT cooperates with maternal Wnt signalling in the formation of the dorsoventral axis. These results demonstrate that maternal VegT directly regulates siamois gene transcription in the formation of the Spemann organizer, and provide further insight into the mechanism underlying the functional interaction between VegT and Wnt signalling during development.
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http://dx.doi.org/10.1387/ijdb.150040dsDOI Listing
November 2016

Hes4 controls proliferative properties of neural stem cells during retinal ontogenesis.

Stem Cells 2012 Dec;30(12):2784-95

UPR CNRS 3294, University Paris-Sud, Orsay, France.

The retina of fish and amphibian contains genuine neural stem cells located at the most peripheral edge of the ciliary marginal zone (CMZ). However, their cell-of-origin as well as the mechanisms that sustain their maintenance during development are presently unknown. We identified Hes4 (previously named XHairy2), a gene encoding a bHLH-O transcriptional repressor, as a stem cell-specific marker of the Xenopus CMZ that is positively regulated by the canonical Wnt pathway and negatively by Hedgehog signaling. We found that during retinogenesis, Hes4 labels a small territory, located first at the pigmented epithelium (RPE)/neural retina (NR) border and later in the retinal margin, that likely gives rise to adult retinal stem cells. We next addressed whether Hes4 might impart this cell subpopulation with retinal stem cell features: inhibited RPE or NR differentiation programs, continuous proliferation, and slow cell cycle speed. We could indeed show that Hes4 overexpression cell autonomously prevents retinal precursor cells from commitment toward retinal fates and maintains them in a proliferative state. Besides, our data highlight for the first time that Hes4 may also constitute a crucial regulator of cell cycle kinetics. Hes4 gain of function indeed significantly slows down cell division, mainly through the lengthening of G1 phase. As a whole, we propose that Hes4 maintains particular stemness features in a cellular cohort dedicated to constitute the adult retinal stem cell pool, by keeping it in an undifferentiated and slowly proliferative state along embryonic retinogenesis.
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http://dx.doi.org/10.1002/stem.1231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3549485PMC
December 2012

A bromodeoxyuridine (BrdU) based protocol for characterizing proliferating progenitors in Xenopus embryos.

Methods Mol Biol 2012 ;917:461-75

Faculty of Life Sciences, University of Manchester, Manchester, England, UK.

BrdU is a thymidine analog that is incorporated into DNA during the S-phase of the cell cycle. BrdU incorporation can be used to quantify the number of cells that are in S-phase in the time period that BrdU is available. Thus, BrdU incorporation is an essential method in the quantitative analysis of cell proliferation, during normal embryonic development or after experimental manipulation. It is a reliable and versatile method that can be easily combined with immunohistochemistry and in situ hybridization to relate cell proliferation with gene expression. BrdU incorporation has been used in all model organisms; here, we describe a protocol adapted for use in Xenopus embryos.
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http://dx.doi.org/10.1007/978-1-61779-992-1_26DOI Listing
January 2013

A large scale screen for neural stem cell markers in Xenopus retina.

Dev Neurobiol 2012 Apr;72(4):491-506

Neurobiology and Development Laboratory, CNRS UPR 3294, Univ Paris-Sud, Orsay, France.

Neural stem cell research suffers from a lack of molecular markers to specifically assess stem or progenitor cell properties. The organization of the Xenopus ciliary marginal zone (CMZ) in the retina allows the spatial distinction of these two cell types: stem cells are confined to the most peripheral region, while progenitors are more central. Despite this clear advantage, very few genes specifically expressed in retinal stem cells have been discovered so far in this model. To gain insight into the molecular signature of these cells, we performed a large-scale expression screen in the Xenopus CMZ, establishing it as a model system for stem cell gene profiling. Eighteen genes expressed specifically in the CMZ stem cell compartment were retrieved and are discussed here. These encode various types of proteins, including factors associated with proliferation, mitotic spindle organization, DNA/RNA processing, and cell adhesion. In addition, the publication of this work in a special issue on Xenopus prompted us to give a more general illustration of the value of large-scale screens in this model species. Thus, beyond neural stem cell specific genes, we give a broader highlight of our screen outcome, describing in particular other retinal cell markers that we found. Finally, we present how these can all be easily retrieved through a novel module we developed in the web-based annotation tool XenMARK, and illustrate the potential of this powerful searchable database in the context of the retina.
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http://dx.doi.org/10.1002/dneu.20973DOI Listing
April 2012

MafA transcription factor identifies the early ret-expressing sensory neurons.

Dev Neurobiol 2010 Jun;70(7):485-97

Institut Curie, Orsay F-91405, France.

Dorsal root ganglia proceed from the coalescence of cell bodies of sensory neurons, which have migrated dorsoventrally from the delaminating neural crest. They are composed of different neuronal subtypes with specific sensory functions, including nociception, thermal sensation, proprioception, and mechanosensation. In contrast to proprioceptors and thermonociceptors, little is known about the molecular mechanisms governing the early commitment and later differentiation into mechanosensitive neurons. This is mainly due to the absence of specific molecular markers for this particular cell type. Using knockout mice, we identified the bZIP transcription factor MafA as the first specific marker of a subpopulation of "early c-ret" positive neurons characterized by medium-to-large diameters. This marker will allow further functional characterization of these neurons.
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http://dx.doi.org/10.1002/dneu.20790DOI Listing
June 2010
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