Zip4/Spo22 Is Required for Class I CO Formation but Not for Synapsis Completion in Arabidopsis thaliana

In budding yeast meiosis, the formation of class I interference-sensitive crossovers requires the ZMM proteins. These ZMM proteins are essential in forming a mature synaptonemal complex, and a subset of these (Zip2, Zip3, and Zip4) has been proposed to compose the core of synapsis initiation complexes (SICs). Zip4/Spo22 functions with Zip2 to promote polymerization of Zip1 along chromosomes, making it a crucial SIC component. In higher eukaryotes, synapsis and recombination have often been correlated, but it is totally unknown how these two processes are linked. In this study, we present the characterization of a higher eukaryote SIC component homologue: Arabidopsis AtZIP4. We show that mutations in AtZIP4 belong to the same epistasis group as Atmsh4 and eliminate approximately 85% of crossovers (COs). Furthermore, genetic analyses on two adjacent intervals of Chromosome I established that the remaining COs in Atzip4 do not show interference. Lastly, immunolocalization studies showed that polymerization of the central element of the synaptonemal complex is not affected in Atzip4 background, even if it may proceed from fewer sites compared to wild type. These results reveal that Zip4 function in class I CO formation is conserved from budding yeast to Arabidopsis. On the other hand, and contrary to the situation in yeast, mutation in AtZIP4 does not prevent synapsis, showing that both aspects of the Zip4 function (i.e., class I CO maturation and synapsis) can be uncoupled

Identification of ASYNAPTIC4, a Component of the Meiotic Chromosome Axis

International audienceDuring the leptotene stage of prophase I of meiosis, chromatids become organized into a linear looped array via a protein axis that forms along the loop bases. Establishment of the axis is essential for the subsequent synapsis of the homologous chromosome pairs and the progression of recombination to form genetic crossovers. Here, we describe ASYNAPTIC4 (ASY4), a meiotic axis protein in Arabidopsis (Arabidopsis thaliana). ASY4 is a small coiled-coil protein that exhibits limited sequence similarity with the carboxyl-terminal region of the axis protein ASY3. We used enhanced yellow fluorescent protein-tagged ASY4 to show that ASY4 localizes to the chromosome axis throughout prophase I. Bimolecular fluorescence complementation revealed that ASY4 interacts with ASY1 and ASY3, and yeast two-hybrid analysis confirmed a direct interaction between ASY4 and ASY3. Mutants lacking full-length ASY4 exhibited defective axis formation and were unable to complete synapsis. Although the initiation of recombination appeared to be unaffected in the asy4 mutant, the number of crossovers was reduced significantly, and crossovers tended to group in the distal parts of the chromosomes. We conclude that ASY4 is required for normal axis and crossover formation. Furthermore, our data suggest that ASY3/ASY4 are the functional homologs of the mammalian SYCP2/SYCP3 axial components

The Arabidopsis BLAP75/Rmi1 Homologue Plays Crucial Roles in Meiotic Double-Strand Break Repair

In human cells and in Saccharomyces cerevisiae, BLAP75/Rmi1 acts together with BLM/Sgs1 and TopoIIIα/Top3 to maintain genome stability by limiting crossover (CO) formation in favour of NCO events, probably through the dissolution of double Holliday junction intermediates (dHJ). So far, very limited data is available on the involvement of these complexes in meiotic DNA repair. In this paper, we present the first meiotic study of a member of the BLAP75 family through characterisation of the Arabidopsis thaliana homologue. In A. thaliana blap75 mutants, meiotic recombination is initiated, and recombination progresses until the formation of bivalent-like structures, even in the absence of ZMM proteins. However, chromosome fragmentation can be detected as soon as metaphase I and is drastic at anaphase I, while no second meiotic division is observed. Using genetic and imunolocalisation studies, we showed that these defects reflect a role of A. thaliana BLAP75 in meiotic double-strand break (DSB) repair—that it acts after the invasion step mediated by RAD51 and associated proteins and that it is necessary to repair meiotic DSBs onto sister chromatids as well as onto the homologous chromosome. In conclusion, our results show for the first time that BLAP75/Rmi1 is a key protein of the meiotic homologous recombination machinery. In A. thaliana, we found that this protein is dispensable for homologous chromosome recognition and synapsis but necessary for the repair of meiotic DSBs. Furthermore, in the absence of BLAP75, bivalent formation can happen even in the absence of ZMM proteins, showing that in blap75 mutants, recombination intermediates exist that are stable enough to form bivalent structures, even when ZMM are absent

A High Throughput Genetic Screen Identifies New Early Meiotic Recombination Functions in Arabidopsis thaliana

Meiotic recombination is initiated by the formation of numerous DNA double-strand breaks (DSBs) catalysed by the widely conserved Spo11 protein. In Saccharomyces cerevisiae, Spo11 requires nine other proteins for meiotic DSB formation; however, unlike Spo11, few of these are conserved across kingdoms. In order to investigate this recombination step in higher eukaryotes, we took advantage of a high-throughput meiotic mutant screen carried out in the model plant Arabidopsis thaliana. A collection of 55,000 mutant lines was screened, and spo11-like mutations, characterised by a drastic decrease in chiasma formation at metaphase I associated with an absence of synapsis at prophase, were selected. This screen led to the identification of two populations of mutants classified according to their recombination defects: mutants that repair meiotic DSBs using the sister chromatid such as Atdmc1 or mutants that are unable to make DSBs like Atspo11-1. We found that in Arabidopsis thaliana at least four proteins are necessary for driving meiotic DSB repair via the homologous chromosomes. These include the previously characterised DMC1 and the Hop1-related ASY1 proteins, but also the meiotic specific cyclin SDS as well as the Hop2 Arabidopsis homologue AHP2. Analysing the mutants defective in DSB formation, we identified the previously characterised AtSPO11-1, AtSPO11-2, and AtPRD1 as well as two new genes, AtPRD2 and AtPRD3. Our data thus increase the number of proteins necessary for DSB formation in Arabidopsis thaliana to five. Unlike SPO11 and (to a minor extent) PRD1, these two new proteins are poorly conserved among species, suggesting that the DSB formation mechanism, but not its regulation, is conserved among eukaryotes

Sartre et la peinture : Sartre préférait-il les mots aux images ?

Quelle place occupe la peinture dans la vie et la philosophie de Sartre ? A-t-il jamais rencontré des peintres qui puissent corroborer ses thèses ? Existe-t-il seulement une esthétique constituée chez ce philosophe qui semblait préférer les mots aux images ? Il semblerait plus juste, dans un premier temps, de parler d’une esthétique « par la négative », dans la mesure où les textes de Sartre à propos de la peinture sont rares, fragmentaires voire inédits ; qui plus est, son rejet de la peinture officielle et des musées semble dominer tout autant ses œuvres littéraires que philosophiques ; et quand il s’agira de définir la peinture, elle sera reléguée au rang d’ « art non-signifiant » au même titre que la sculpture, la poésie ou la musique, dans cette œuvre liminaire que représente en 1947 Qu’est-ce que la littérature ? : ce arts ne sont pas engagés « de la même manière » que la littérature. N’est-ce pas alors l’ambivalence de la notion d’analogon, mais aussi celle d’engagement, qui constitue la clé de cette esthétique picturale ? S’il en est une, elle s’affirme en effet surtout à partir de 1947 comme « esthétique de la Présence », puisque la matière analogique va progressivement devenir la première préoccupation sartrienne. Sartre persiste à rejeter l’immobilisme pictural pour lui préférer le matiérisme d’un Tintoret, qui peint en sculpteur et devient le réalisateur de ses toiles, dans tous les sens du terme, annonçant tous les autres peintres « existentialistes ». C’est pourquoi Sartre semble avoir trouvé dans la peinture non seulement un moyen de totaliser le réel, mais aussi, par voie de conséquence, sa propre pensée.What's the place of painting in Sartre's life and philosophy ? Did he find painters who corroborate his philosophical arguments? Is there a pictorial esthetics by Sartre ? We could first talk about a pictorial esthetics which would be "in the negative" : indeed the Sartrian texts about painting are rare, fragmentary, in a disorganised manner, or even unpublished ; there is also a very strong reject of official painting through official galeries and portraits ; and the painter, the musician, the sculptor or the poet are not involved “in the same way” as the writer : they are only “non-significant arts”. If there is a pictorial esthetics by Sartre, it would be therefore an “esthetics of the Presence”, where the role of matter will be more and more important, after 1947: it is the ambivalent status of analogon and involvment in Sartre's philosophy which seems to be the key of his esthetics. The irreducible materiality is going to have more and more importance : he insists progressively on the matter whose things are made, on the real action of the painter, on the canva in itself. Sartre rejects immobility in painting and proposes a constant apology of movement. That's why he chooses Le Tintoret: the Venitian paints as if he was a film-maker. Therefore the painter will be really involved in his own work of art : he lives a creative situation. Finally we could say that Sartre has found in painting a good way to reach absolute and to totalize the reality, but also to totalize his own thought

L'éducation des patients sous antivitamine K (justificatifs et premières approches)

MONTPELLIER-BU Pharmacie (341722105) / SudocSudocFranceF

Sartre et la peinture (pour une définition de l'"analogon" pictural)

Quelle place occupe la peinture dans la vie et la philosophie de Sartre? A-t-il jamais rencontré des peintres qui puissent corroborer ses thèses? Existe-t-il seulement une esthétique constituée chez ce philosophe qui semblait préférer les mots aux images? Il semblerait plus juste, dans un premier temps, de parler d'une Esthétique par la négative , dans la mesure où les textes de Sartre à propos de la peinture sont rares, fragmentaires voire inédits; qui plus est, son rejet de la peinture officielle et des musées semble dominer tout autant ses œuvres littéraires que philosophiques; et quand il s'agira de définir la peinture, elle sera reléguée au rang d' art non-signifiant au même titre que la sculpture, la poésie ou la musique, dans cette œuvre liminaire que représente en 1947 Qu'est-ce que la Littérature ? : ces arts ne sont pas engagés de la même manière que la littérature. N'est-ce pas alors l'ambivalence de la notion d'analogon, mais aussi celle d'engagement, qui constitue la clé de cette esthétique picturale? S'il en est une, elle s'affirme en effet surtout à partir de 1947 comme Esthétique de la Présence , puisque la matière analogique va progressivement devenir la première préoccupation sartrienne, comme une compression du signifié dans le signifiant. Sartre rejette alors l'immobilisme pictural pour lui préférer le matiérisme d'un Tintoret, qui peint en sculpteur et devient le réalisateur de ses toiles, dans tous les sens du terme, annonçant tous les autres peintres existentialistes . C'est pourquoi Sartre semble avoir trouvé dans la peinture non seulement un moyen de totaliser le réel, mais aussi, par voie de conséquence, sa propre pensée, via une redéfinition plus matiériste de l'analogon pictural, annonçant, à bien des égards, l'Esthétique Merleau-pontienne.PARIS1-BU Pierre Mendès-France (751132102) / SudocSudocFranceF

Compteur de vehicules a detection par champ magnetique

Available from INIST (FR), Document Supply Service, under shelf-number : RL 288 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEMinistere de l'Equipement, des Transports et du Logement (METL), 92 - Puteaux (France). Direction de la Recherche et des Affaires Scientifiques et Techniques (DRAST)FRFranc