DNA dynamics vary according to macrodomain topography in the E. coli chromosome

The organization of the Escherichia coli chromosome has been defined genetically as consisting of four insulated macrodomains and two less constrained regions. Here we have examined the movement of chromosomal loci by tracking fluorescent markers in time-lapse microscopy during a complete cell cycle. Analysing the positioning, the segregation pattern and the motility of markers allowed us to show that the dynamic behaviour of loci belonging to various macrodomains and less constrained regions is radically different. In macrodomains constraints on mobility are apparent whereas in non-structured regions, markers exhibited a greater motility that may explain their ability to interact with flanking macrodomains. Following replication, duplicated markers belonging to macrodomains show a colocalization step and this landmark is not apparent in non-structured regions. Chromosome segregation occurs in three steps: first, the origin-proximal half of the chromosome consisting of the Ori macrodomain and the two non-structured region segregates concomitantly in a short period of time. Second, the Right and Left macrodomains segregate progressively following the genetic map. Third, the Ter macrodomain is rapidly segregated before division, after a significant period of colocalization. Macrodomain territories defined as cellular spaces occupied by the different macrodomains can be identified.     

Electrostatic interactions between hyaluronan and proteins at pH 4: how do they modulate hyaluronidase activity

Hyaluronan (HA) hydrolysis catalyzed by hyaluronidase (HAase) is inhibited at low HAase over HA ratio and low ionic strength, because HA forms electrostatic complexes with HAase, which is unable to catalyze hydrolysis. Bovine serum albumin (BSA) was used as a model to study the HA-protein electrostatic complexes at pH 4. At low ionic strength, there is formation of (i) neutral insoluble complexes at the phase separation and (ii) small positively-charged or large negatively-charged soluble complexes whether BSA or HA is in excess. According to the ionic strength, different types of complex are formed. Assays for HA and BSA led to the determination of the stoichiometry of these complexes. HAase was also shown to form the various types of complex with HA at low ionic strength. Finally, we showed that at 0 and 150 mmol L(-1) NaCl, BSA competes with HAase in forming complexes with HA and thus induces HAase release resulting in a large increase in the hydrolysis rate. These results, in addition to data in the literature, show that HA-protein complexes, which can exist under numerous and varied conditions of pH, ionic strength and protein over HA ratio, might control the in vivo HAase activity.     

Modified glutamine catabolism in macrophages of Ucp2 knock-out mice

Uncoupling protein 2 (UCP2) belongs to a family of transporters of the mitochondrial inner membrane and is reported to uncouple respiration from ATP synthesis. Our observation that the amino acid glutamine specifically induces UCP2 protein expression prompted us to investigate metabolic consequences of a UCP2 knockdown (Ucp2-KO) when glutamine is offered as a substrate. We found that Ucp2-KO macrophages incubated in the presence of glutamine exhibit a lower ammonium release, a decreased respiratory rate, and an intracellular accumulation of aspartate. Therefore, we conclude that UCP2 expression is required for efficient oxidation of glutamine in macrophages. This role of UCP2 in glutamine metabolism appears independent from the uncoupling activity of UCP2.     

Accounting for weather and time-of-day parameters when analysing count data from monitoring programs

Problems induced by heterogeneity in species and individuals detectability are now well recognized when analysing count data. Yet, most recent techniques developed to handle this problem are still hardly applicable to many monitoring schemes, and do not provide abundance estimates at the point count scale. Here, we show how using simple weather variables can be a useful surrogate to detect variability in species detectability. We further look for a potential bias or loss in statistical power based on count data while ignoring weather and time-of-day variables. We first used the French Breeding Bird Survey to test how each of the counts of the 97 most common breeding species was influenced by weather and time-of-day variables. We assessed how the estimation of each species response to fragmentation could be influenced by correcting counts with such variables. Among 97 species, 75 were affected by at least one of the five weather and time-of-day variables considered. Despite these strong influences, the relationship between species abundance and fragmentation was not biased when not controlling counts for weather and time-of-day variables and further found no improvement in statistical power when accounting for these variables. Our results show that simple variables can be very powerful to assess how species detectability is influenced by weather conditions but they are inconsistent with any specific bias due to heterogeneous detectability. We suggest that raw count data can be used without any correction in case the sources of variation in detectability could be considered independent to the factor of interest.     

A genome scan for quantitative trait loci affecting the Salmonella carrier-state in the chicken

Selection for increased resistance to Salmonella colonisation and excretion could reduce the risk of foodborne Salmonella infection. In order to identify potential loci affecting resistance, differences in resistance were identified between the N and 6₁ inbred lines and two QTL research performed. In an F2 cross, the animals were inoculated at one week of age with Salmonella enteritidis and cloacal swabs were carried out 4 and 5 wk post inoculation (thereafter called CSW4F2 and CSW4F2) and caecal contamination (CAECF2) was assessed 1 week later. The animals from the (N × 6₁) × N backcross were inoculated at six weeks of age with Salmonella typhimurium and cloacal swabs were studied from wk 1 to 4 (thereafter called CSW1BC to CSW4BC). A total of 33 F₂ and 46 backcross progeny were selectively genotyped for 103 and 135 microsatellite markers respectively. The analysis used least-squares-based and non-parametric interval mapping. Two genome-wise significant QTL were observed on Chromosome 1 for CSW2BC and on Chromosome 2 for CSW4F2, and four suggestive QTL for CSW5F2 on Chromosome 2, for CSW5F2 and CSW2BC on chromosome 5 and for CAECF2 on chromosome 16. These results suggest new regions of interest and the putative role of SAL1.     

Genetic traces of east-to-west human expansion waves in Eurasia

In this study, we describe the landscape of human demographic expansions in Eurasia using a large continental Y chromosome and mitochondrial DNA dataset. Variation at these two uniparentally-inherited genetic systems retraces expansions that occurred in the past 60 ky, and shows a clear decrease of expansion ages from east to west Eurasia. To investigate the demographic events at the origin of this westward decrease of expansion ages, the estimated divergence ages between Eurasian populations are compared with the estimated expansion ages within each population. Both markers suggest that the demographic expansion diffused from east to west in Eurasia in a demic way, i.e., through migrations of individuals (and not just through diffusion of new technologies), highlighting the prominent role of eastern regions within Eurasia during Palaeolithic times.     

Degradation of lyophilized lipid/DNA complexes during storage: The role of lipid and reactive oxygen species

The presence of trace amounts of metal ions in nonviral vector formulations can significantly affect the stability of lipid/DNA complexes (lipoplexes) during acute freeze-drying. The goal of the present study was to evaluate the generation of reactive oxygen species (ROS) in dried formulations of lipoplexes and in their individual components (lipid or naked DNA). The experiments were conducted in the presence or absence of a transition metal (Fe²⁺). Lipoplexes and their individual components were formulated in trehalose and subjected to lyophilization and stored for a period of up to 2 months at + 60 °C. Physico-chemical characteristics and biological activity were evaluated at different time intervals. Generation of ROS during storage was determined by adding a fluorescence probe to the formulations prior to freeze-drying. We also monitored the formation of thiobarbituric reactive substances (TBARS). Our results show that ROS and TBARS form during storage in the dried state. Our findings also suggest that degradation is more rapid in the presence of lipid, even in the absence of metal. We also showed that dried naked DNA formulations are more stable without the lipid component. Effective strategies are then needed to minimize the formation and accumulation of oxidative damage of lipoplexes during storage.     

Relationship between antagonistic leg muscles co-contractions and body centre of gravity mechanics in different level gait disorders.

Body centre of gravity (CG) mechanics and electromyographic activity of flexor-extensor antagonistic muscles of the lower limb were simultaneously recorded in lowest and middle-level gait disorders. Muscle co-contractions between tibialis anterior and triceps surae, and between rectus femoris and hamstrings were evaluated. CG mechanics was assessed by the external mechanical work (W(ext)) done to translate the CG with respect to the ground, and the recovery quantifying the efficacy of gait mechanism by the amount of energy transferred between gravitational potential and kinetic energies of the CG. The results showed a strong relationship between CG mechanics and the co-contractions of the main flexor-extensor ankle muscles. In middle-level gait disorders, our results suggest that the ankle antagonistic muscle co-contractions and the CG mechanics could provide information about gait mechanism and the integrity level of the locomotor program.     

Floristic and life form diversity in post-pasture successions on a Mediterranean island (Corsica)

The landscapes of the French island of Corsica are the result of thegrazing tradition which has always occupied a pivotal position in the island'seconomy. Furthermore, in the last fifty years, a reduction in the pressure fromhuman activity has lead to changes in plant cover. This article intends tostudythe evolution of dynamic mechanisms during the secondary successions and theeffect of changes in vegetation on plant diversity. Our study was based on asimultaneous study of 375 plots carried out between May and September from 1996to 1998. We studied the floristic composition of each stage both qualitatively(life form, adaptive strategy and seed dispersal mode) and quantitatively(species richness, equitability, Shannon index). The results show a change inspecies and environmental conditions, with a progressive move from heliophilicgrassland and low shrub species with an S or SR strategy, anemochoric and withahigh tolerance for soil quality to a final stage of dense forest composed ofcompetitive (C or CS) zoochoric or barochoric phanerophytes. Moreover, theturning point in Corsica in terms of floristic diversity lies between 20 and 55years after land abandonment. Successions are due to a series of rapidinteractions. Thus, when a site is given reserve or protected area status, weneed to take into account the fact that it will evolve according to thebiological traits of the species. From a research point of view, we need tolookat process diversity and the role of each of the species present during thesuccessions.