Ressources pour la classe de première générale et technologique - Sciences de la vie et de la Terre - Série S

http://eduscol.education.fr/pid23214-cid57514/ressources-pour-la-classe-de-premiere-du-lycee-general-et-technologique.htm

Characterization of a MAF1 knockout mouse model

L'ARN polymérase 3 transcrit un petit groupe de gènes fortement exprimés et impliqués dans plusieurs mécanismes moléculaires. Les ARNs de transfert ou ARNt représentent plus ou moins la moitié du transcriptome de l'ARN polymérase 3. Ils sont directement impliqués dans la traduction des protéines en agissant comme transporteurs d'acides aminés qui sont incorporés à la chaîne naissante de polypeptides. Chez des levures cultivées dans un milieu jusqu'à épuisement des nutriments, Maf1 réprime la transcription par l'ARN polymérase 3, favorisant ainsi l'économie énergétique cellulaire. Dans un modèle de cellules de mammifères, MAF1 réprime aussi la transcription de l'ARN polymérase 3 dans des conditions de stress, cependant il n'existe aucune donnée quant à son rôle chez un mammifère vivant. Pendant mon doctorat, j'ai utilisé une souris délétée pour le gène Maf1 afin de connaître les effets de ce gène chez un mammifère. Etonnamment, la souris Maf1-­‐/-­‐ est résistante à l'obésité même si celle-­‐ci est nourrie avec une nourriture riche en matières grasses. Des études moléculaires et de métabolomiques ont montré qu'il existe des cycles futiles de production et dégradation des lipides et des ARNt, ce qui entraîne une augmentation de la dépense énergique et favorise la résistance à l'obésité. En plus de la caractérisation de la souris Maf1-­‐/-­‐, pendant ma thèse j'ai également développé une méthode afin de normaliser les données de ChIP-­‐sequencing. Cette méthode est fondée sur l'utilisation d'un contrôle interne, représenté ici par l'ajout d'une quantité fixe de chromatine provenant d'un organisme différent de celui étudié. La méthode a amélioré considérablement la reproductibilité des valeurs entre réplicas biologiques. Elle a aussi révélé des différences entre échantillons issus de conditions différentes. Une occupation supérieure de l'ARN polymérase 3 sur les gènes Pol 3 chez les souris Maf1 KO entraîne une augmentation du niveau de précurseurs d'ARNt, ayant pour effet probable la saturation de la machinerie de maturation des ARNt. En effet, chez les souris Maf1 KO, le pourcentage d'ARNt modifiés est plus faible que chez les souris type sauvage. Ce déséquilibre entre le niveau de précurseurs et d'ARNt matures entraîne une diminution de la traduction protéique. Ces résultats ont permis d'identifier de nouvelles fonctions pour la protéine MAF1, comme étant une protéine régulatrice à la fois de la transcription mais aussi de la traduction et en étant un cible potentielle au traitement à l'obésité. -- RNA polymerase III (Pol 3) transcribes a small set of highly expressed genes involved in different molecular mechanisms. tRNAs account for almost half of the Pol 3 transcriptome and are involved in translation, bringing a new amino into the nascent polypeptide chain. In yeast, under nutrient deprivation, Maf1 acts for cell energetic economy by repressing Pol 3 transcription. In mammalian cells, MAF1 also represses Pol 3 activity under conditions of serum deprivation or DNA damages but nothing is known about its role in a mammalian organism. During my thesis studies, I used a Maf1 KO mouse model to characterize the effects of Maf1 deletion in a living animal. Surprisingly, the MAF1 KO mouse developed an unexpected phenotype, being resistant to high fat diet-­‐induced obesity and displaying an extended lifespan. Molecular and metabolomics characterizations revealed futile cycles of lipids and tRNAs, which are produced and immediately degraded, which increases energy consumption in the Maf1 KO mouse and probably explains in part the protection to obesity. Additionally to the mouse characterization, I also developed a method to normalize ChIP-­‐seq data, based on the addition of a foreign chromatin to be used as an internal control. The method improved reproducibility between replicates and revealed differences of Pol 3 occupancy between WT and Maf1 KO samples that were not seen without normalization to the internal control. I then established that increased Pol 3 occupancy in the Maf1 KO mouse liver was associated with increased levels of tRNA precursor but not of mature tRNAs, the effective molecules involved in translation. The overproduction of precursor tRNAs associated with the deletion of Maf1 apparently overwhelms the tRNA processing machinery as the Maf1 KO mice have lower levels of fully modified tRNAs. This maturation defect directly impacts on translation efficiency as polysomic fractions and newly synthetized protein levels were reduced in the liver of the Maf1 KO mouse. Altogether, these results indicate new functions for MAF1, a regulator of both transcription and translation as well as a potential target for obesity treatment

Health consequences of female genital mutilation/cutting in the Gambia, evidence into action

Background: Female Genital Mutilation/Cutting (FGM/C) is a harmful traditional practice with severe health complications, deeply rooted in many Sub-Saharan African countries. In The Gambia, the prevalence of FGM/C is 78.3% in women aged between 15 and 49 years. The objective of this study is to perform a first evaluation of the magnitude of the health consequences of FGM/C in The Gambia. Methods: Data were collected on types of FGM/C and health consequences of each type of FGM/C from 871 female patients who consulted for any problem requiring a medical gynaecologic examination and who had undergone FGM/C in The Gambia. Results: The prevalence of patients with different types of FGM/C were: type I, 66.2%; type II, 26.3%; and type III, 7.5%. Complications due to FGM/C were found in 299 of the 871 patients (34.3%). Even type I, the form of FGM/C of least anatomical extent, presented complications in 1 of 5 girls and women examined. Conclusion: This study shows that FGM/C is still practiced in all the six regions of The Gambia, the most common form being type I, followed by type II. All forms of FGM/C, including type I, produce significantly high percentages of complications, especially infections

Usinage des composites renforcés en fibres de carbone : stratégie de surfaçage pour limiter les efforts de coupe

International audienceLes matériaux composites sont des multi-matériaux (matrice + renfort) souvent anisotropes. De part leur constitution, ces matériaux posent de nombreuses problématiques lors de leur usinage. Les défauts générés lors de l'opération de parachèvement de la pièce peuvent être : la décohésion de deux plis de matière, l'écaillage des fibres, ou la dégradation thermique de la résine polymère. De plus le caractère abrasif des fibres de carbone tend à user rapidement les arêtes de coupe, augmentant ainsi la génération des défauts cités précédemment. Dans cet article, nous proposons une stratégie d'usinage en surfaçage limitant les efforts sur l'arête. Le matériau utilisé est un composite Carbone/résine époxy (T800S/M21), il a été observé que la résultante des efforts s'appliquant sur l'outil est maximum lorsque l'angle entre la vitesse de coupe et la fibre est entre 0° et 45°. Connaissant les orientations des plis dans la matière, il est alors possible de jouer sur l'engagement de la fraise et la profondeur de passe pour limiter les efforts de coupe sur l'outil

Public libraries embrace citizen science: Strengths and challenges

Can public libraries become hubs for citizen science? In line with the principles of citizen science, this question was answered collaboratively with librarians from the Barcelona Network of Public Libraries who performed two hands-on activities. One activity was a training course taken by 30 librarians from 24 different libraries which enabled them to envisage citizen science implementation at each library. The other activity consisted of co-creating a citizen social science project and involved 40 library users, seven librarians from three different cities, and professional scientists. The analysis considers the perspectives of both librarians and users, through participant observation, surveys, and a focus group to identify strengths and challenges. The overall results suggest that public libraries can offer leadership in the promotion of citizen science and contribute to the mission of public libraries to act as local community hubs. The main challenges identified were related to the complexity of collaboration, uncertainty regarding research co-creation, and participant retention strategies

Citizen science at public libraries: Data on librarians and users perceptions of participating in a citizen science project in Catalunya, Spain

As libraries struggle to keep pace with the changing societal landscape, emerging practices such as citizen science (CS) initiatives are being incorporated to reinforce the idea of public libraries as gathering, meeting, and collaboration spaces within the context of shared community and shared learning resources. However, there is little empirical evidence of whether the most open and participatory ways that CS puts forward can converge with and be nurtured by the essence of public libraries. Also, the roles of librarians and users in the 'next generation public library' have been under-developed. As the number of CS initiatives at public libraries grows, so does the need to collect evidence on the impact and the capacity of assimilation of CS practices. The data describes librarians and users' perceptions of participating in a citizen science project. Two hands-on activities for librarians of the Barcelona Network of Public Libraries were implemented. One was a training course for 30 librarians from 24 libraries which allowed them to envisage citizen science implementation in each library. The second activity consisted in the co-creation of a citizen social science project. 40 library users, 7 librarians from 3 different cities, and professional scientists, were involved. The data on librarians and users' perception was collected through participant observation, surveys, and a focus group to identify strengths and challenges of implementing citizen science at public libraries. The data covers librarians and users attitudes towards citizen science, their motivations to participate, their perceived ability to implement a citizen science project (as for librarians) or to contribute to science (as for library users), and the participants intention to keep engaged with citizen science, drawing on the Theory of Planned Behavior. Responses to closed-ended survey questions are analyzed at a descriptive level. The qualitative feedback from the focus group and the open-ended survey question on motivations is subjected to a thematic analysis. The data offers interesting insights to identify opportunities and challenges of implementing citizen science at public libraries, contributing to the debate over the public library's mission as local community hub

10 ideas to include the RRI perspective in STEM education

The report includes in its first section RRI: A short introduction a brief summary about what RRI is and which are its antecedents. In the second section RRI in STEM education: What and why? a discussion about why including RRI perspective in STEM education is important and what implications would this new perspective imply. In the latter section, a more nuanced definition is proposed than is hitherto available of STEM education pillar. Finally, the last section 10 ideas to include the RRI perspective in STEM education offers a useful guide of ten big ideas about how RRI perspective could be brought to STEM Education, considering the pillars and processes that characterize the RRI paradigm and linking the big ideas with the several methodologies in STEM education