1,721,022 research outputs found
A novel allele of ASY3 is associated with greater meiotic stability in autotetraploid Arabidopsis lyrata
Full text linkIn this study we performed a genotype-phenotype association analysis of meiotic stability in 10 autotetraploid Arabidopsis lyrata and A. lyrata/A. arenosa hybrid populations collected from the Wachau region and East Austrian Forealps. The aim was to determine the effect of eight meiosis genes under extreme selection upon adaptation to whole genome duplication. Individual plants were genotyped by high-throughput sequencing of the eight meiosis genes (ASY1, ASY3, PDS5b, PRD3, REC8, SMC3, ZYP1a/b) implicated in synaptonemal complex formation and phenotyped by assessing meiotic metaphase I chromosome configurations. Our results reveal that meiotic stability varied greatly (20-100%) between individual tetraploid plants and associated with segregation of a novel ASYNAPSIS3 (ASY3) allele derived from A. lyrata. The ASY3 allele that associates with meiotic stability possesses a putative in-frame tandem duplication (TD) of a serine-rich region upstream of the coiled-coil domain that appears to have arisen at sites of DNA microhomology. The frequency of multivalents observed in plants homozygous for the ASY3 TD haplotype was significantly lower than in plants heterozygous for ASY3 TD/ND (non-duplicated) haplotypes. The chiasma distribution was significantly altered in the stable plants compared to the unstable plants with a shift from proximal and interstitial to predominantly distal locations. The number of HEI10 foci at pachytene that mark class I crossovers was significantly reduced in a plant homozygous for ASY3 TD compared to a plant heterozygous for ASY3 ND/TD. Fifty-eight alleles of the 8 meiosis genes were identified from the 10 populations analysed, demonstrating dynamic population variability at these loci. Widespread chimerism between alleles originating from A. lyrata/A. arenosa and diploid/tetraploids indicates that this group of rapidly evolving genes may provide precise adaptive control over meiotic recombination in the tetraploids, the very process that gave rise to them
Study of the role of neddylation in the regulation of meiotic recombination
No full textLa recombinaison homologue est essentielle à la réparation des lésions de l’ADN ainsi qu’à la ségrégation correcte des chromosomes en méiose. Une étape importante de la recombinaison méiotique est la formation des crossovers (CO). Au cours de ma thèse, j’ai mis en évidence un nouveau mécanisme de régulation de la recombinaison méiotique. J'ai montré que les cycles d'activation et de désactivation des cullin-RING ligases (CRL) sont absolument nécessaires à la recombinaison méiotique. Les CRL sont activées par neddylation et désactivées par la deneddylation. De plus, elles peuvent aussi être inhibées par la séquestration via la protéine CAND1. Mon travail a démontré que ces trois niveaux de régulation des CRL jouent des rôles cruciaux dans la recombinaison homologue méiotique chez A. thaliana. J’ai montré qu'AXR1, un composant clé de la machinerie de neddylation, est nécessaire à la localisation correcte des CO méiotiques et à la recombinaison homologue somatique. J’ai aussi prouvé que le processus de deneddylation médié par CSN5A est nécessaire à la formation des CO. J'ai obtenu des données montrant que cette régulation de la localisation des CO agit à travers la régulation d’un complexe CRL4. Enfin, j’ai pu montrer que l'inhibiteur des CRL, CAND1, est requis pour la formation de plus de 90 % des CO. En utilisant des outils génétiques et cytologiques, j'ai montré que CAND1 agit probablement sur la régulation du biais inter-homologue. L’ensemble de ces données, met l’accent sur un nouveau mécanisme de la régulation de la recombinaison homologue, connectant pour la première fois la méiose et l’ubiquitination via les cullin-RING Ligases.Homologous recombination is essential to all living organisms in order to repair DNA damages. In addition, a large majority of organisms use homologous recombination in meiosis to ensure proper chromosome segregation. A main step of meiotic recombination is crossover (CO) formation. During my PhD, I was able to highlight a new pathway controlling meiotic recombination. I showed that cycles of activation and deactivation of cullin-RING ligases (CRLs) are absolutely required for correct meiosis. CRLs are activated by neddylation, and deactivated by deneddylation. In addition, they can also be inhibited by sequestration by the CAND1 protein. My work demonstrated that these three levels of CRL regulation play crucial roles in meiotic homologous recombination in A. thaliana. First, I showed that AXR1, a key component of the neddylation machinery, is required for the correct localisation of meiotic COs and for somatic homologous recombination. Second, I showed that the deneddylation process mediated by CSN5A is also necessary for normal CO formation. I obtained evidence that this regulation of CO position is likely to be mediated by a CRL4 complex. Last, I could show that the CRL inhibitor, CAND1, is required for the formation of up to 90% of the COs. Using genetic and cytological tools, I showed that CAND1 probably acts on the regulation of the inter-homolog bias. Considering all these data, my work draws the attention to a new mechanism regulating meiotic homologous recombination, connecting for the first time meiosis to CRL-mediated ubiquitylation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Plant Meiosis: Methods and Protocols
No full textMeiosis is one of the most critical processes in eukaryotes, required for continuation of species and generation of new variation. In plants, meiotic recombination is by far the most important source of genetic variation. In Plant Meiosis: Methods and Protocols, expert researchers in the field detail methods for molecular cytogenetics and chromosome analysis in plants. These state-of -the-art protocols allow studying the organization and behavior of the genetic material in a wide range of both model and crop species. Written in the highly successful Methods in Molecular Biology™series format, chapters include introductions to their respective topics, lists of the necessar
Meiotic double-strand breaks formation in the plant model Arabidopsis thaliana
No full textLa méiose est essentielle pour tous les organismes à reproduction sexuée car cette division cellulaire spécialisée conduit à la formation de gamètes. Au cours de la méiose, la formation de bivalents est une étape clé dans la répartition équilibrée des chromosomes homologues. Dans la majorité des espèces, la formation de ces bivalents repose sur le mécanisme de la recombinaison homologue qui est un mécanisme de réparation des cassures double brin (CDB) de l’ADN. En méiose, la cassure est programmée et provoquée par l’action de Spo11. A.thaliana contient deux homologues SPO11-1 et SPO11-2 qui ne sont pas redondants dans la formation des CDB. Spo11 est une protéine apparentée à la sous-unité A des topoVI d’Archaea. Or, les topoVI d’Archaea fonctionnent en hétérotétramère composé de deux sous-unités A et deux sous-unités B pour former une cassure double brin (CDB) mais jusqu'à mon travail de thèse, aucun homologue méiotique de sous unité B n'avait été identifié. Au cours de ma thèse, j’ai caractérisé la fonction méiotique de la protéine MTOPVIB et montré que c’est un homologue structural de la sous-unité B des TopoVI d’Archaea. Par différentes approches, j’ai montré que MTOPVIB est nécessaire à l’hétérodimérisation de SPO11-1 avec SPO11-2 et je propose que chez A. thaliana, un complexe catalytique de type TopoVI composé de MTOPVIB, SPO11-1, et SPO11-2 est nécessaire à la formation des CDB méiotiques. Chez A. thaliana, en plus de SPO11-1, SPO11-2 et MTOPVIB, quatre autres protéines sont nécessaires à la formation des CDB : PRD1, PRD2, PRD3 et DFO. Par des approches double hybride, j’ai analysé le réseau d’interaction entre ces protéines de « cassure ». Les résultats suggèrent que ces protéines interagiraient au sein d’un « super » complexe essentiel à la formation des CDB méiotiques.Meiosis is an essential step in sexual reproduction because it leads to the formation of haploid gametes. During meiosis, the formation of bivalents is a key step for the balanced chromosome distribution. In most species, the formation of bivalents lies on the mechanism of homologous recombination that is a repair mechanism for double stranded DNA breaks (DSB). In meiosis, DSB formation is programmed and provoked by the action of Spo11. A.thaliana contains two SPO11-1 and SPO11-2 counterparts which are not redundant in the formation of DSB. Spo11 is related to the A subunit of Archaea topoVI. However, Archaea topoVI operate through a heterotetramer composed of two A subunits and two B subunits but until my thesis work, no meiotic homolog of the B subunit had been identified. During my thesis, I characterized the meiotic function of the new protein MTOPVIB and showed that it shares structural similarities with the B subunit of Archaea TopoVI. Using different strategies, I also demonstrated that MTOPVIB is necessary to the SPO11-1/ SPO11-2 heterodimerization strongly suggesting that in A. thaliana, a catalytic TopoVI like complex is necessary for the formation of meiotic DSB. In addition to SPO11-1, SPO11-2, and MTOPVIB, four other proteins are necessary for the formation of meiotic DSB in A. thaliana : PRD1, PRD2, PRD3 and DFO. By yeast two hybrid approach, I analysed the interaction network between the "DSB" proteins. The results suggest that these proteins could act in a "super" complex which would be essential to the formation of DSBs
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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