Les déterminants des performances scolaires des élèves marocains

Le Maroc fait partie des pays en développement dont le niveau des acquis des élèves reste relativement faible. En dépit des efforts engagés en vue d’améliorer en partie la qualité des apprentissages, les résultats des enquêtes internationales et nationales révèlent de faibles niveaux des acquis. Dès lors, l’objectif de cet article est de revenir sur les facteurs qui influencent les performances scolaires des élèves. Nous nous intéressons plus spécifiquement aux déterminants microéconomiques de la qualité de l’éducation à travers les performances des élèves. Les études sur les déterminants des performances scolaires sont riches d’enseignement. Les premières contributions se sont focalisées sur le rôle de l’environnement familial dans l’explication de la réussite des élèves (Coleman, 1966, par exemple). D’autres, plus récemment, ont abordé les facteurs liés à l’établissement scolaire. Pour autant, les contributions récentes mettent en avant l’importance à la fois de l’environnement familial et de l’école (Hanushek, 2003). Des travaux plus récents oulignent également l’influence des pairs sur les performances scolaires. Le présent travail s’inscrit dans cette logique. Son originalité se situe à un double niveau. La première réside dans la mise en évidence de l’ensemble des facteurs explicatifs des performances des élèves et des inégalités scolaires. Malgré l’existence d’une littérature abondante sur le sujet, cette question n’a pas été abordée, à notre connaissance, dans le cas marocain. La seconde cherche à corriger les problèmes d’endogénéité dans les modèles multiniveaux. Enfin, La technique d’imputation adoptée permet de traiter de façon pertinente les valeurs manquantes dans les bases de données. Cet article est structuré en trois parties. La première aborde la littérature empirique sur les déterminants de la réussite scolaire des élèves. La deuxième partie examine le modèle utilisé et décrit la base de données du Programme national d’évaluation des acquis (PNEA). Elle examine l’approche et la méthodologie utilisée. Enfin, la troisième partie traite des résultats obtenus et nous permet de formuler les principaux enseignements pouvant être tirés de nos résultats en matière de politiques publiques

Enzyme engineering of bovine trypsin

Bovine trypsin is a biocatalyst widely used to cleave recombinant proteins during the downstream processing of therapeutic proteins, and is used particularly for insulin bioprocessing. Evolution has produced a wealth of natural biocatalysts over billions of years, which are generally not optimised for specific industrial applications. Bovine trypsin has a relatively broad specificity towards cleavage at the C-terminal end of arginine or lysine residues. Consequently it has a tendency to cleave alternative sites in the insulin process leading to loss of yield and more complex downstream processing. This project describes efforts to alter the primary specificity of bovine trypsin. Trypsin variants were generated using two traditional random mutagenesis methods tailored to improve the chance of producing a useful mutant. These were focussed error prone PCR (fepPCR) and multiple-site saturation mutagenesis (MSSM). In order to select residues useful for MSSM, a study of the correlation between (1) mutations enhancing specificity or activity and (2) sequence entropy and distance of mutations from the active site was carried out based on past examples of directed and rational evolution. This analysis along with biochemical information for trypsin aided the selection of two specificity "hotspots" for random mutagenesis, each comprising four residues. These hotspots were regions in the trypsin gene close to or directly involved in substrate binding. Depending on the mutagenesis method used, the size of the mutant libraries differed considerably. For example, fepPCR of a 522 bp region of the trypsin gene required approximately 3,000 mutants to encompass all possibilities whereas the library size for MSSM was 160,000 for each of the selected four-residue regions. Two alternative library screening approaches, with different throughput capabilities, were tested to isolate mutants of interest. Automated colony screening was considered suitable for the smaller fepPCR library and consisted of the following steps: (1) transformation of a plasmid library into E. coli BL21-Gold(DE3) cells (2) fermentation of individual colonies in 384 square-well microplates (3) lysis of the cultures and (4) spectrophotometric activity measurement on a variety of substrates. The best mutant had a 2.54-fold improvement in arginine specificity. For the larger MSSM libraries, a nutritional selection method was developed using E. coli arg-auxotrophic strains. An alternative approach to generating trypsin variants was also explored based on the known ability of bovine trypsin to autolyse into "pseudo-trypsins". Since these pseudo-trypsins are variants of the native form of the enzyme, it was anticipated that they would have specificities different to that of the native enzyme. Efforts were made to separate the variants via novel chromatographic techniques and to characterise them with respect to molecular weight and specificity. Finally, the activity profile of bovine trypsin was comprehensively carried out on a range of novel substrates, and a comparison made between commercially available bovine trypsin and Eli Lilly's recombinant trypsin. Similar reaction profiles were returned by both enzymes on all substrates with the previously unreported finding that there was a preference for cleavage at the C-terminal end of two positively charged basic residues (i.e. KR or RR rather than GR)

In Vivo Assessment of Stem Cells for Treating Neurodegenerative Disease: Current Approaches and Future Prospects

In recent years, stem cell-related therapies have been widely applied for treating neurodegenerative disease. Despite their potential, stem cell tracking and imaging techniques for the evaluation of in vivo proof-of-concept (PoC) therapies have not been sufficiently represented in the research area. This review summarizes the recent approaches that have been used for tracking and imaging engrafted stem cells in vivo. Furthermore, we introduce tissue clearing technology that can be applied to develop three-dimensional in vivo experiments. Monitoring stem cell survival and migration and graft-host relationships is a useful strategy to evaluate the therapeutic efficacy of regenerative medicine approaches in neurodegenerative disease

Cuscuta Species Identification Based on the Morphology of Reproductive Organs and Complete Chloroplast Genome Sequences

The genus Cuscuta (Convolvulaceae) comprises well-known parasitic plants. Cuscuta species are scientifically valuable, as their life style causes extensive crop damage. Furthermore, dried seeds of C. chinensis are used as a Korean traditional herbal medicine. Despite the importance of Cuscuta species, it is difficult to distinguish these plants by the naked eye. Moreover, plastid sequence information available for Cuscuta species is limited. In this study, we distinguished between C. chinensis and C. japonica using morphological characterisation of reproductive organs and molecular characterisation of chloroplast genomes. The differences in morphological characteristics of reproductive organs such as style, stigma, infrastaminal scale, seed shape and testa ornamentation were useful for distinguishing between C. japonica and C. chinensis. Analysis of chloroplast genomes revealed drastic differences in chloroplast genome length and gene order between the two species. Although both species showed numerous gene losses and genomic rearrangements, chloroplast genomes showed highly similar structure within subgenera. Phylogenetic analysis of Cuscuta chloroplast genomes revealed paraphyletic groups within subgenera Monogynella and Grammica, which is consistent with the APG IV system of classification. Our results provide useful information for the taxonomic, phylogenetic and evolutionary analysis of Cuscuta and accurate identification of herbal medicine

Comparative Morphological, Ultrastructural, and Molecular Studies of Four Cicadinae Species Using Exuvial Legs

Previous studies have suggested that exuviae can be used for the identification of cicada species, but the precise characteristics that differ among species have not been determined. Thus, we performed the first comparative analyses of the leg morphology, ultrastructure, and mitochondrial DNA sequences of exuviae of four dominant cicada species in Korea, Hyalessa maculaticollis (Motschulsky, 1866), Meimuna opalifera (Walker, 1850), Platypleura kaempferi (Fabricius, 1794) and Cryptotympana atrata (Fabricius, 1775), the source of Cicadidae Periostracum, a well-known traditional medicine. A morphological analysis revealed that the profemur length, femoral tooth angle, and distance between the intermediate and last tooth of the femoral comb are useful characteristics for identification. We also evaluated the usefulness of the size, degree of reflex, and number of spines on the mid-legs and hind legs as diagnostic features. An ultrastructural study showed that Meimuna opalifera has a unique surface pattern on the legs. The sequences obtained using exuviae were identical to previously obtained sequences for adult tissues. Moreover, in a phylogenetic analysis using CO1 sequences, each species formed a monophyletic cluster with high bootstrap support. Accordingly, multiple methodological approaches using exuviae might provide highly reliable identification tools. The integrative data provide useful characteristics for the exuviae-based identification of closely related species and for further taxonomic and systematic studies of Cicadinae

Successful Management of Periampullary Diverticular Bleeding with Hemoclipping Using Side-viewing Endoscope during Endoscopic Retrograde Cholangiopancreatography

Periampullary diverticulum is commonly found during endoscopy and can occur at any age although its prevalence increases with age. Periampullary diverticular bleeding is a rare and difficult to diagnose during clinical practice because of its unique appearance and location. This often can lead to massive bleeding and interfere with adequate bleeding control. Endoscopic management on duodenal diverticular bleeding is limited compared to colonic diverticular bleeding due to lack of experience. Herein, we report a case of active bleeding from a periampullary diverticulum during bile duct stone extraction diagnosed by side-viewing endoscope and successfully controlled using hemoclips without any complications. (Korean J Gastroenterol 2016;67:146-149

ADSC-Based Cell Therapies for Musculoskeletal Disorders: A Review of Recent Clinical Trials

Recently published clinical trials involving the use of adipose-derived stem cells (ADSCs) indicated that approximately one-third of the studies were conducted on musculoskeletal disorders (MSD). MSD refers to a wide range of degenerative conditions of joints, bones, and muscles, and these conditions are the most common causes of chronic disability worldwide, being a major burden to the society. Conventional treatment modalities for MSD are not sufficient to correct the underlying structural abnormalities. Hence, ADSC-based cell therapies are being tested as a form of alternative, yet more effective, therapies in the management of MSDs. Therefore, in this review, MSDs subjected to the ADSC-based therapy were further categorized as arthritis, craniomaxillofacial defects, tendon/ligament related disorders, and spine disorders, and their brief characterization as well as the corresponding conventional therapeutic approaches with possible mechanisms with which ADSCs produce regenerative effects in disease-specific microenvironments were discussed to provide an overview of under which circumstances and on what bases the ADSC-based cell therapy was implemented. Providing an overview of the current status of ADSC-based cell therapy on MSDs can help to develop better and optimized strategies of ADSC-based therapeutics for MSDs as well as help to find novel clinical applications of ADSCs in the near future