Density-dependence across dispersal stages in a hermaphrodite land snail: insights from discrete choice models

Dispersal movements, i.e. movements leading to gene flow, are key behaviours with important, but only partially understood, consequences for the dynamics and evolution of populations. In particular, density-dependent dispersal has been widely described, yet how it is determined by the interaction with individual traits, and whether density effects differ between the three steps of dispersal (departure, transience, and settlement), remains largely unknown. Using a semi-natural landscape, we studied dispersal choices of Cornu aspersum land snails, a species in which negative effects of crowding are well documented, and analysed them using dispersal discrete choice models, a new method allowing the analysis of dispersal decisions by explicitly considering the characteristics of all available alternatives and their interaction with individual traits. Subadults were more dispersive than adults, confirming existing results. In addition, departure and settlement were both density dependent: snails avoided crowded patches at both ends of the dispersal process, and subadults were more reluctant to settle into crowded patches than adults. Moreover, we found support for carry-over effects of release density on subsequent settlement decisions: snails from crowded contexts were more sensitive to density in their subsequent immigration choices. The fact that settlement decisions were informed indicates that costs of prospecting are not as important as previously thought in snails, and/or that snails use alternative ways to collect information, such as indirect social information (e.g. trail following). The observed density-dependent dispersal dynamics may play an important role in the ability of C. aspersum to successfully colonise frequently human-disturbed habitats around the world.     

The choice of controls in a case-control study on WBC-DNA adducts and metabolic polymorphisms

The choice of the control group is a key issue in case-control studies, particularly in studies of molecular epidemiology. We discuss the potential bias introduced by different options. To exemplify the consequences of different choices, we have analysed two sets of controls in the context of a case-control study on bladder cancer: 55 were patients with urological conditions (cystitis, prostate hypertrophy), while 49 had a miscellany of medical or surgical conditions. We measured DNA adducts in white blood cells (WBC) by ³²P-postlabelling and a series of metabolic polymorphisms (GSTM1, GSTT1, GSTP1, NAT2, NQO1). While no statistically significant differences were found for metabolic polymorphisms, the two series of controls showed different concentrations of DNA adducts, suggesting that conditions related to bladder cancer or intermediate steps leading to bladder cancer, such as chronic cystitis, may be associated with higher adduct levels. An association between DNA adduct levels and infection has been noted before in experimental animals: both in lung and in the skin, an inflammatory response increased the biologically effective doses of polycyclic aromatic hydrocarbons. An alternative explanation is confounding; in fact, after adjustment for the level of consumption of fruit and vegetables (but not for smoking) the difference between the two control groups was no longer statistically significant. In conclusion, the choice of controls in studies of molecular epidemiology has subtle methodological implications, including confounding of metabolic/molecular measurements by complex exposures such as diet.     

Discriminatory power of RAPD,PCR-RFLP and southern blot analyses of ureCD or ureA gene probes on Helicobacter pylori isolates

The genetic diversity of 33 Nigerian Helicobacter pylori isolates were studied using RAPD, PCR-RFLP and Southern blot analysis of ureA or ureCD gene probes. RAPD was able to distinguish the following number of isolates using the primers 3880: 5'-AAGAGCCCGT-3' (28), 3881 :5'-AACGCGCAAC-3' (33) and OPH8 :5'-GAAACACCCC-3' (25). Southern blot analysis using the ureCD probe was also able to distinguish the 12 isolates tested into ten different patterns. The PCR-RFLP technique distinguished all 33 isolates into six types. In conclusion, considering typeability, discriminatory power, and convenience, RAPD with the 3881 primer was considered the most useful technique.     

The interaction of peripheral proteins and membranes studied with alpha-lactalbumin and phospholipid bilayers of various compositions

To characterize the interaction of peripheral proteins and membranes at the molecular level, we studied the reversible association of bovine alpha-lactalbumin (BLA) with lipid bilayers composed of different molecular forms of phosphatidylserine or equimolar mixtures of these phosphatidylserine forms and egg yolk phosphatidylcholine. At pH 4.5, almost all BLA (>90%) associates to negatively charged small unilamellar vesicles. The conformational changes that binding to these bilayers induced on the protein were characterized by circular dichroism and fluorescence spectroscopy. Because binding of BLA to negatively charged vesicles is reverted by adjusting the pH back to >6.0, we also investigated the conformation of the membrane-bound protein by NMR-monitored H-D exchange of the backbone amide protons. The conformation adopted by BLA bound to these bilayers resembles a molten globule-like state but the negative ellipticity at 222 nm and the apparent alpha-helix content of the bound protein senses the changes in the physical properties of the membrane. Binding to bilayers in the gel state appears to correlate with an increased amount of alpha-helical structure and with a lower extent of integration into the membrane, corresponding to the adsorbed protein, while the opposite is found for BLA bound to vesicles in the liquid-crystalline phase, corresponding to the embedded conformation. A common feature for the membrane-bound conformations of BLA is that the amphipathic helix C (residues 86 to 99) is an important determinant for the adsorption and further integration of the protein into the membrane.     

Ultraviolet A radiation transiently disrupts gap junctional communication in human keratinocytes

Ultraviolet A (UVA) (320-400 nm)radiation is known to cause cutaneous aging and skin cancer. We studiedthe effect of UVA (365 nm) radiation on the human epidermis by focusingon keratinocyte gap junction-mediated intercellular communication(GJIC). We observed a dose-dependent 10-fold decrease in GJIC inducedby UVA in normal human keratinocytes. This decrease in GJIC wasassociated with time-dependent internalization of connexin43 (Cx43).UVA radiation also damaged the actin cytoskeleton, as shown bymicrofilament disappearance. Importantly, the decrease in GJIC wastransient when keratinocytes were irradiated with 10 J/cm²UVA, with a return to baseline values after 8 h. Concomitantly, Cx43 was relocalized and the actin cytoskeleton was restored. UVAirradiation and 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment activated protein kinase C and reduced GJIC. However, Cx43localization and phosphorylation were differently regulated by the twotreatments. This suggests that at least two different pathways maymediate the observed fall in GJIC. These findings identify keratinocyteGJIC as a new UVA target that might sensitize human skin to photoagingand cancer formation.

     

A Variable Gene in a Conserved Region of the Helicobacter pylori Genome: Isotopic Gene Replacement or Rapid Evolution?

The present study concerns the identification of a novel coding sequence in a region of the Helicobacter pylori genome, located between JHP1069/HP1141 and JHP1071/HP1143 according to the numbering of the J99 and 26695 reference strains, respectively, and spanning three different coding DNA sequences (CDSs). The CDSs located at the centre of this locus were highly polymorphic, as determined by the analysis of 24 European isolates, 3 Asian, and 3 African isolates. Phylogenetic and molecular evolutionary analyses showed that the CDSs were not restricted to the geographical origin of the strains. Despite a very high variability observed in the deduced protein sequences, significant similarity was observed, always with the same protein families, i.e. ATPase and bacteriophage receptor/invasion proteins. Although this variability could be explained by isotopic gene replacement via horizontal transfer of a gene with the same function but coming from a variety of sources, it seems more likely that the very high sequence variation observed at this locus is the result of a strong selection pressure exerted on the corresponding gene product. The CDSs identified in the present study could be used as strain specific markers.