Influence de la nature et de l'abondance des proies sur l'augmentation des effectifs de deux coccinelles prédatrices de la cochenille du manioc au Congo

Résumé Les variations d'abondance des 2 cochenillesPhenacoccus manihoti Matile-Ferrero etFerrisia virgata Cockerell et des 2 prédateurs CoccinellidaeHyperaspis senegalensis hottentotta Mulsant etExochomus flaviventris Mader sont étudiées dans une parcelle de manioc. La colonisation de cette dernière parE. flaviventris est précoce, en présence de faibles niveaux numériques des 2 proies, mais avec une dominance deF. virgata; celle d'H. s. hottentotta intervient un mois plus tard en relation semble-t-il avec la présence d'une population deP. manihoti abondante et jeune. Nos observations font ressortir une dynamique des populations propre à chaque espèce de coccinelle, conditionnée par l'abondance de l'une ou l'autre des proies, la structure des colonies de chaque cochenille et les conditions climatiques (température) qui interviennent en synergie. Ainsi, la réponse numérique deH. s. hottentotta, plus forte que celle d'E. flaviventris, semble en relation plus étroite avecP. manihoti. PourE. flaviventris il appara?t difficile de séparer ce qui revient à chaque espèce de cochenille:F. virgata joue sans doute un r?le important pour son implantation dans les champs, puis sa raréfaction, mais c'est probablementP. manihoti qui permet l'augmentation de ses effectifs.      

Sensory receptors of the ovipositor ofTrichogramma maidis [Hym.:Trichogrammatidae]

Sensory receptors of the ovipositor ofTrichogramma maidis are described. Sense organs are found on the 2^nd valvifers (1 type), on the tip of the 3^rd valvulae (2 types) and on the 1^st valvulae (4 types). The nature and possible functions of these sensilla are discussed.      

Retroviral insertional activation of the c-myb proto-oncogene in a Marek's disease T-lymphoma cell line.

Marek's disease virus (MDV) is an avian herpesvirus that causes, in chickens, a lymphoproliferative disease characterized by malignant transformation of T lymphocytes. The rapid onset of polyclonal tumors indicates the existence of MDV-encoded oncogenic products. However, the molecular basis of MDV-induced lymphoproliferative disease and latency remains largely unclear. Several lines of evidence suggest that MDV and Rous-associated virus (RAV) might cooperate in the development of B-cell lymphomas induced by RAV. Our present results indicate for the first time that MDV and RAV might also act synergistically in the development of T-cell lymphomas. We report an example of an MDV-transformed T-lymphoblastoid cell line (T9) expressing high levels of a truncated C-MYB protein as a result of RAV integration within one c-myb allele. The chimeric RAV-c-myb mRNA species initiated in the 5' long terminal repeat of RAV are deprived of sequences corresponding to c-myb exons 1 to 3. The attenuation of MDV oncogenicity has been strongly related to structural changes in the MDV BamHI-D and BamHI-H DNA fragments. We have established that both DNA restriction fragments are rearranged in the T9 MDV-transformed cells. Our results suggest that retroviral insertional activation of the c-myb proto-oncogene is a critical factor involved in the maintenance of the transformed phenotype and the tumorigenic potential of this T-lymphoma cell line.     

Linkage disequilibrium and extended haplotypes in the HLA-A to D6S105 region: implications for mapping the hemochromatosis gene (HFE)

The hemochromatosis gene (HFE) maps to 6p21.3, in close linkage with the HLA Class I genes. Linkage disequilibrium (LD) studies were designed to narrow down the most likely candidate region for HFE, as an alternative to traditional linkage analysis. However, both the HLA-A and D6S105 subregions, which are situated 2–3 cM and approximately 3 Mb apart, have been suggested to contain HFE. The present report extends our previous study based upon the analysis of a large number of HFE and normal chromosomes from 66families of Breton ancestry. In addition to the previously used RFLP markers spanning the 400-kb surrounding HLA-A, we examined three microsatellites: D6S510, HLA-F, and D6S105. Our combined data not only confirm a peak of LD at D6S105, but also reveal a complex pattern of LD over the i82 to D6S105 interval. Within our ethnically well-defined population of Brittany, the association of HFE with D6S105 is as great as that with HLA-A, while the internal markers display a lower LD. Fine haplotype analysis enabled us to identify two categories of haplotypes segregating with HFE. In contrast to the vast majority of normal haplotypes, 50% of HFE haplotypes are completely conserved over the HLA-A to D6S105 interval. These haplotypes could have been conserved through recombination suppression, selective forces and/or other evolutionary factors. This particular haplotypic configuration might account for the apparent inconsistencies between genetic linkage and LD data, and additionally greatly complicates positional cloning of HFE through disequilibrium mapping.The authors contributed equally to this work     

Adaptive surface antigen variation in Mycoplasma bovis to the host immune response

Abstract The variability of predominant Mycoplasma bovis surface antigens in the presence of specific immune pressure was analyzed in an in vitro assay to determine if M. bovis could escape immune destruction. We have shown that serum antibodies from immunized or experimentally infected calves and monoclonal antibodies which specifically react with previously characterized or as yet undefined major M. bovis membrane surface proteins cause repression of expression or shortening of the target protein, or induce switching to expression of an antigenically distinct variant protein. We have further demonstrated that removal of the inducing antibody results in reversion to the original phenotype. These results suggest that the level of expression and the length of M. bovis surface antigens in the host is modulated by cognate antibodies. According to the surface antigenic variation systems, random selection of preexisting variants resistant to antibody-mediated inhibition or direct regulation of gene expression may be means by which this organism evades host immune defences.     

Core temperature variability in diving king penguins (Aptenodytes patagonicus): a preliminary analysis

Core temperature was determined in two king penguins living in the wild at Ile de la Possession, Crozel Archipelago, using implantable four-channel temperature loggers. Core temperatures derived from bird no. 1 (sensor placed under the sternum, in the vicinity of the liver and upper stomach) were closely correlated with diving activity (as determined by an external light recorder), and ranged from 38.3°C, (on land) to a minimum of 37.2°C during a dive. Core temperatures measured in bird no. 2 showed that temperatures near the heart were generally 1°C lower than those under the sternum or in the lower abdomen. Core temperatures declined continuously during dives (by 0.8, 1.2 and 2.7°C in the lower abdomen, under the sternum and near the heart, respectively) and showed precipitous drops to 35°C, probably associated with ingestion of food. Temperatures measured near the heart fluctuated over a period of 288 s, corresponding to the duration (from the literature) of the surface/dive cycle. The relevance of these findings with respect to diving physiology, blood perfusion of tissues, tissue metabolism and aerobic dive limits is discussed.     

Human neurotrophin-3: A one-step peptide mapping method and complete disulfide characterization of the recombinant protein

Human neurotrophin-3 (NT-3) is a member of the nerve growth factor (NGF) family of neurotrophic factors, and the recombinant protein is being developed as a therapeutic for neurodegenerative diseases. The final product purity and lot-to-lot variation are monitored routinely by peptide mapping. However, only the N-terminal region of NT-3 was susceptible to proteolysis under native conditions. Complete digestion required that the protein be chemically modified by reduction and S-alkylation prior to proteolysis. Complete proteolytic degradation of the protein was achieved simply by an intial denaturation of NT-3 in 6 M guanidinium chloride (pH 6) for 2 hr at 37°C, followed by a tenfold dilution with the digestion buffer (0.1 M Tris-HCl, 1 mM CaCl₂ at pH 7.0) and immediate addition of chymotrypsin at 1% by weight. Direct comparison of the peptide map with an identical aliquot that had been reduced and alkylated also allowed the establishment of the cystine linkages present in NT-3: Cys¹⁴ to Cys⁷⁹, Cys⁵⁷ to Cys¹⁰⁸, and Cys⁶⁷ to Cys¹¹⁰. This disulfide structure is homologous to the NGF family of neurotrophic factors.