Etude de la respiration, à l’état isolé, des haplotypes de l’abeille tunisienne Apis mellifera intermissa (Buttel Reepen 1906) (Hymenoptera : Apidae)

L’étude de la respiration de l’abeille domestique, Apis mellifera intermissa, à l’état isolé a été réalisée sur les quatre haplotypes existant en Tunisie : A1, A4, A8 et A9 et sous différentes températures : 0°, 10°, 15°, 20°, 25°, 30° et 35°C. Des mesures effectuées sur 1000 abeilles isolées (250 de chaque haplotype) ont montré que la consommation d’oxygène de l’abeille varie en fonction de la température. L’intensité respiratoire des haplotypes augmente progressivement à partir de 0°C pour atteindre son maximum à 15°C. Au-delà de cette température, la consommation d’oxygène de l’abeille diminue progressivement. Pour les basses températures (0° et 10°C), la respiration de l’abeille dépend aussi du facteur génétique et la consommation d’oxygène est faible mais ne s’annule pas. Cette étude a montré qu’il existe une différence de consommation d’oxygène entre les haplotypes A1 et A8 et les haplotypes A4 et A9 pour les basses températures. Le déclenchement de la thermogenèse chez les haplotypes A1 et A8 se produit à 15°C, alors que chez les haplotypes A4 et A9, il a lieu à une température plus basse et qui est de 10°C.     

Antifungal activity of Bacillus thuringiensis strains and their efficacy against the cotton leaf worm Spodoptera littoralis

Bacillus thuringiensis strains that belong to B. thuringiensis, B. kurstaki and soil-isolated B.t. were assessed in the following phytopathogenic: Rhizoctonia solani, that had their mycelial growth decreased after incubation in the presence of the bacterial strains. The bacteria have also pathogenic effect against the insect pest Spodoptera littoralis. The isolate B.t. D-1 and the B.t. kurstaki HD-203 were found to be inhibiting R. solani, the strain B. kurstaki HD-203 displayed the highest percentage of inhibition (64%) and B.t. D-1 showed 49% of inhibition. Antagonistic activity was maintained up to pH 8.5, and the antifungal activity was stable to heat at 70?°C for 1?h. Minimal inhibitory concentrations were 152 and 131?μl/ ml for B.t. D-1 and B. kurstaki HD-203, respectively. The two strains also have high efficacy against S. littoralis larvae, B.t. D-1 gave 70% and the B. kurstaki HD-203 strain gave 80% mortality after seven days of treatment.     

Genetic structure of Tunisian ethnic groups revealed by paternal lineages

Tunisia has experienced a variety of human migrations that have modeled the myriad cultural groups inhabiting the area. Both Arabic and Berber-speaking populations live in Tunisia. Berbers are commonly considered as in situ descendants of peoples who settled roughly in Palaeolithic times, and posterior demographic events such as the arrival of the Neolithic, the Arab migrations, and the expulsion of the "Moors" from Spain, had a strong cultural influence. Nonetheless, the genetic structure and the population relationships of the ethnic groups living in Tunisia have been poorly assessed. In order to gain insight into the paternal genetic landscape and population structure, more than 40 Y-chromosome single nucleotide polymorphisms and 17 short tandem repeats were analyzed in five Tunisian ethnic groups (three Berber-speaking isolates, one Andalusian, and one Cosmopolitan Arab). The most common lineage was the North African haplogroup E-M81 (71%), being fixed in two Berber samples (Chenini-Douiret and Jradou), suggesting isolation and genetic drift. Differential levels of paternal gene flow from the Near East were detected in the Tunisian samples (J-M267 lineage over 30%); however, no major sub-Saharan African or European influence was found. This result contrasts with the high amount of sub-Saharan and Eurasian maternal lineages previously described in Tunisia. Overall, our results reveal a certain genetic inter-population diversity, especially among Berber groups, and sexual asymmetry, paternal lineages being mostly of autochthonous origin. In addition, Andalusians, who are supposed to be migrants from southern Spain, do not exhibit any substantial contribution of European lineages, suggesting a North African origin for this ethnic group.     

Partial leptin deficiency favors diet-induced obesity and related metabolic disorders in mice

Partial leptin deficiency is not uncommon in the general population. We hypothesized that leptin insufficiency could favor obesity, nonalcoholic steatohepatitis (NASH), and other metabolic abnormalities, particularly under high calorie intake. Thus, mice partially deficient in leptin (ob/+) and their wild-type (+/+) littermates were fed for 4 mo with a standard-calorie (SC) or a high-calorie (HC) diet. Some ob/+ mice fed the HC diet were also treated weekly with leptin. Our results showed that, when fed the SC diet, ob/+ mice did not present significant metabolic abnormalities except for elevated levels of plasma adiponectin. Under high-fat feeding, increased body fat mass, hepatic steatosis, higher plasma total cholesterol, and glucose intolerance were observed in +/+ mice, and these abnormalities were further enhanced in ob/+ mice. Furthermore, some metabolic disturbances, such as blunted plasma levels of leptin and adiponectin, reduced UCP1 expression in brown adipose tissue, increased plasma liver enzymes, beta-hydroxybutyrate and triglycerides, and slight insulin resistance, were observed only in ob/+ mice fed the HC diet. Whereas de novo fatty acid synthesis in liver was decreased in +/+ mice fed the HC diet, it was disinhibited in ob/+ mice along with the restoration of the expression of several lipogenic genes. Enhanced expression of several genes involved in fatty acid oxidation was also observed only in ob/+ animals. Leptin supplementation alleviated most of the metabolic abnormalities observed in ob/+ fed the HC diet. Hence, leptin insufficiency could increase the risk of obesity, NASH, glucose intolerance, and hyperlipidemia in a context of calorie overconsumption.     

Variation in volatile leaf oils of five Eucalyptus species harvested from Jbel Abderrahman arboreta (Tunisia)

Hydrodistillation of the dried leaves of five species of the genus Eucalyptus L' Hér ., viz., E. dundasii Maiden , E. globulus Labill ., E. kitsoniana Maiden , E. leucoxylon F. Muell ., and E. populifolia Hook ., harvested from Jbel Abderrahman arboreta (region of Nabeul, northeast of Tunisia) in April 2006, afforded essential oils in yields varying from 0.9±0.3 to 3.8±0.6%, dependent on the species. E. globulus and E. Kitsoniana provided the highest and the lowest percentage of essential oil amongst the species examined, respectively. Analysis by GC (RI) and GC/MS allowed the identification of 127 compounds, representing 93.8 to 98.7% of the total oil composition. The contents of the different samples varied according to the species. The main components were 1,8‐cineole ( 2 ; 4.7–59.2%), followed by α‐pinene ( 1 ; 1.9–23.6%), trans‐pinocarveol ( 6 ; 3.5–21.6%), globulol ( 8 ; 4.3–12.8%), p‐cymene ( 3 ; 0.5–6.7%), α‐terpineol (1.5–4.5%), borneol (0.2–4.4%), pinocarvone (1.1–3.8%), aromadendrene (1.4–3.4%), isospathulenol (0.0–1.9%), fenchol ( 4 ; 0.1–2.5%), limonene (1.0–2.4%), epiglobulol (0.6–2.1%), viridiflorol ( 9 ; 0.8–1.8%), and spathulenol (0.1–1.6%). E. leucoxylon was the richest species in 2 . Principal component analysis (PCA) and hierarchical cluster analysis (HCA) separated the five Eucalyptus leaf essential oils into four groups, each constituting a chemotype.     

M19 modulates skeletal muscle differentiation and insulin secretion in pancreatic β-cells through modulation of respiratory chain activity

Mitochondrial dysfunction due to nuclear or mitochondrial DNA alterations contributes to multiple diseases such as metabolic myopathies, neurodegenerative disorders, diabetes and cancer. Nevertheless, to date, only half of the estimated 1,500 mitochondrial proteins has been identified, and the function of most of these proteins remains to be determined. Here, we characterize the function of M19, a novel mitochondrial nucleoid protein, in muscle and pancreatic β-cells. We have identified a 13-long amino acid sequence located at the N-terminus of M19 that targets the protein to mitochondria. Furthermore, using RNA interference and over-expression strategies, we demonstrate that M19 modulates mitochondrial oxygen consumption and ATP production, and could therefore regulate the respiratory chain activity. In an effort to determine whether M19 could play a role in the regulation of various cell activities, we show that this nucleoid protein, probably through its modulation of mitochondrial ATP production, acts on late muscle differentiation in myogenic C2C12 cells, and plays a permissive role on insulin secretion under basal glucose conditions in INS-1 pancreatic β-cells. Our results are therefore establishing a functional link between a mitochondrial nucleoid protein and the modulation of respiratory chain activities leading to the regulation of major cellular processes such as myogenesis and insulin secretion.     

Induction of DNA fragmentation, chromosome aberrations and micronuclei by cisplatin in rat bone-marrow cells: protective effect of recombinant human erythropoietin

Cisplatin (Cisp) is one of the most effective chemotherapeutic agents. However, at higher doses several side effects may occur. Recombinant human erythropoietin (rhEPO), a glycoprotein regulating haematopoiesis, has recently been shown to exert an important cyto-protective effects in many tissues. The purpose of this study was to explore whether rhEPO protects against Cisp-induced genotoxicity in rat bone-marrow cells. Adult male Wistar rats were divided into six groups of 18 animals each: control group, rhEPO-alone group, Cisp-alone group and three rhEPO+Cisp-groups (pre-, co- and post-treatment condition, respectively). Our results show that Cisp induced a noticeable genotoxic effect in rat bone-marrow cells. In all types of treatment, rhEPO significantly decreased the frequency of micronuclei, the percentage of chromosome aberrations and the level of DNA damage. The protective effect of rhEPO was more efficient when it was administrated 24h before exposure to Cisp.     

Towards a characterization of the locomotor activity rhythm of the supralittoral isopod Tylos europaeus

Freshly collected samples of Tylos europaeus from Korba beach (northeast of Tunisia) were housed in an environmental cabinet at controlled temperature (18°C?±?.5°C) and photoperiod. Locomotor activity was recorded under two photoperiodic regimens by infrared actography every 20?min by multichannel data loggers. One regimen simulated the natural light-dark cycle on the day of collection, whereas the second imposed a state of continuous darkness on all individuals. Under entraining conditions, the animals displayed rhythmic activity, in phase with the period of darkness, whereas in continuous darkness these isopods exhibited a strong endogenous rhythm with circadian and semidiurnal components at mean periods of τ (h:min)?=?25:09?±?01:02?h and τ?=?12:32?±?00:26?h, respectively. Under free-running conditions, this endogenous rhythm showed significant intraspecific variability.     

Intra‐annual variation of the spatiotemporal distribution and abundance of Talitridae and Oniscidea (Crustacea,Peracarida) at Bizerte Lagoon (northern Tunisia)

During 1 year from spring 2007 to winter 2008, we conducted four seasonal samplings along a transect in the supralittoral zone of Bizerte Lagoon at Menzel Jmil (Tunisia) to study the intra‐annual variation of Peracarida diversity, Talitridae and Oniscidea. For each season, one transect was studied and quadrates were placed successively from the shoreline to the road backing the shore. Talitridae and Oniscidea were the most abundant taxa in our samples reaching highest densities in summer, when fourteen species were found. The minimum and maximum values of species richness of Talitridae were observed in winter (four species) and summer (eight species), respectively, while for Oniscidea, species richness ranged from one species in winter and five species in spring. Both Talitridae and Oniscidea exhibited intra‐annual variation in their spatial distribution; in that, they moved away from the shoreline in winter and were found near the waterline in the other seasons. ANOVA test shows a high significant correlation between both Talitridae with Suaeda maritima and Oniscidea with the plants S. maritima,Salicornia arabica and Obione portulacoides.     

Noncanonical mismatch repair as a source of genomic instability in human cells

Mismatch repair (MMR) is a key antimutagenic process that increases the fidelity of DNA replication and recombination. Yet genetic experiments showed that MMR is required for antibody maturation, a process during which the immunoglobulin loci of antigen-stimulated B cells undergo extensive mutagenesis and rearrangements. In an attempt to elucidate the mechanism underlying the latter events, we set out to search for conditions that compromise MMR fidelity. Here, we describe noncanonical MMR (ncMMR), a process in which the MMR pathway is activated by various DNA lesions rather than by mispairs. ncMMR is largely independent of DNA replication, lacks strand directionality, triggers PCNA monoubiquitylation, and promotes recruitment of the error-prone polymerase-η to chromatin. Importantly, ncMMR is not limited to B cells but occurs also in other cell types. Moreover, it contributes to mutagenesis induced by alkylating agents. Activation of ncMMR may therefore play a role in genomic instability and cancer.