March flies and European Cenozoic palaeoclimates (Diptera: Bibionidae)

The proportions of the different bibionid genera are used to estimate the temperature changes between the Late Eocene and the Late Miocene in Western Europe. The genus Plecia is a good indicator of the warm Cenozoic palaeoclimates. We propose a new approach for the estimation of the value of the palaeoclimatic information that could be obtained by actualistic inferences using extinct taxa. Other taxa (i.e. Mastotermitidae) that could appear a priori better palaeoclimatic indicators result to be less sensitive than bibionids to temperature changes. Intraspecific and intrageneric morphological diversity is explored for the genera Bibio, Penthetria and Plecia, showing the difficulties to characterize the fossil bibionid species.     

Orientation and foraging movements in a patchy environment by the ant Serrastruma lujae (formicidae-myrmicinae)

Serrastruma lujae ants individually search for collembolans in the leaf litter of humid tropical forests. During the dry season, collembolans aggregate in wet patches randomly scattered in the dry litter where numerous single workers come hunting from their nest. We simulated this situation in the laboratory, and observed that workers seem to be able to use the humidity gradient direction to efficiently orient themselves towards a wet patch. Once the patch has been reached, they exhibit area-concentrated searching,consisting, in particular, of adopting a high sinuosity and a low speed. After capturing a collembolan, the ants return to their nest along nearly straight paths. This ability may rely on a spatial memory of the nest location by means of a path-integration process. In the absence of prey, however, various behaviours were observed after an unsuccessful search. Comparisons between these data and the results obtained with a homogeneously wet environment simulating the rainy season situation showed that these ants do not simply respond to the humidity level but are also sensitive to the degree of patchiness of their environment. They can therefore be said to be able to adapt suitably to the considerable climatic changes they encounter during the year.     

Orthosteric Binding of ρ-Da1a,a Natural Peptide of Snake Venom Interacting Selectively with the α1A-Adrenoceptor

ρ-Da1a is a three-finger fold toxin from green mamba venom that is highly selective for the α_1A-adrenoceptor. This toxin has atypical pharmacological properties, including incomplete inhibition of ³H-prazosin or ¹²⁵I-HEAT binding and insurmountable antagonist action. We aimed to clarify its mode of action at the α_1A-adrenoceptor. The affinity (pKi 9.26) and selectivity of ρ-Da1a for the α_1A-adrenoceptor were confirmed by comparing binding to human adrenoceptors expressed in eukaryotic cells. Equilibrium and kinetic binding experiments were used to demonstrate that ρ-Da1a, prazosin and HEAT compete at the α_1A-adrenoceptor. ρ-Da1a did not affect the dissociation kinetics of ³H-prazosin or ¹²⁵I-HEAT, and the IC₅₀ of ρ-Da1a, determined by competition experiments, increased linearly with the concentration of radioligands used, while the residual binding by ρ-Da1a remained stable. The effect of ρ-Da1a on agonist-stimulated Ca²⁺ release was insurmountable in the presence of phenethylamine- or imidazoline-type agonists. Ten mutations in the orthosteric binding pocket of the α_1A-adrenoceptor were evaluated for alterations in ρ-Da1a affinity. The D106^3.32A and the S188^5.42A/S192^5.46A receptor mutations reduced toxin affinity moderately (6 and 7.6 times, respectively), while the F86^2.64A, F288^6.51A and F312^7.39A mutations diminished it dramatically by 18- to 93-fold. In addition, residue F86^2.64 was identified as a key interaction point for ¹²⁵I-HEAT, as the variant F86^2.64A induced a 23-fold reduction in HEAT affinity. Unlike the M1 muscarinic acetylcholine receptor toxin MT7, ρ-Da1a interacts with the human α_1A-adrenoceptor orthosteric pocket and shares receptor interaction points with antagonist (F86^2.64, F288^6.51 and F312^7.39) and agonist (F288^6.51 and F312^7.39) ligands. Its selectivity for the α_1A-adrenoceptor may result, at least partly, from its interaction with the residue F86^2.64, which appears to be important also for HEAT binding.     

Wandering epithelial cells in the rabbit embryo milk line: A preliminary scanning electron microscope study

In order to confirm the previous results obtained during experimental studies on mammary gland organogenesis and elucidate by what means epidermal cells are clustered together into a protruding ridge, the rabbit embryo milk line was examined under the scanning electron microscope. The discovery of wandering epithelial cells strengthens the current hypothesis that cell migration is a fundamental process during milk line morphogenesis.     

Two different β-lactamase genes are present in Streptomycees cacaoi

Two beta-lactamase genes called blaL and blaU have been cloned independently in Liège and in Ume?, from Streptomyces cacaoi. Genes blaL and blaU were found to differ largely in their nucleotide sequences, although the encoded proteins both belonged to the class A of beta-lactamases (active-site serine penicillinases). DNA-hybridization and polymerase chain reaction assays have now demonstrated that both blaL and blaU genes were present in the S. cacaoi strains used in Liège and in Ume?.     

Characterization of an Atypical Superoxide Dismutase from Sinorhizobium meliloti

Sinorhizobium meliloti Rm5000 is an aerobic bacterium that can live free in the soil or in symbiosis with the roots of leguminous plants. A single detectable superoxide dismutase (SOD) was found in free-living growth conditions. The corresponding gene was isolated from a genomic library by using a sod fragment amplified by PCR from degenerate primers as a probe. The sodA gene was located in the chromosome. It is transcribed monocistronically and encodes a 200-amino-acid protein with a theoretical M(r) of 22,430 and pI of 5. 8. S. meliloti SOD complemented a deficient E. coli mutant, restoring aerobic growth of a sodA sodB recA strain, when the gene was expressed from the synthetic tac promoter but not from its own promoter. Amino acid sequence alignment showed great similarity with Fe-containing SODs (FeSODs), but the enzyme was not inactivated by H(2)O(2). The native enzyme was purified and found to be a dimeric protein, with a specific activity of 4,000 U/mg. Despite its Fe-type sequence, atomic absorption spectroscopy showed manganese to be the cofactor (0.75 mol of manganese and 0.24 mol of iron per mol of monomer). The apoenzyme was prepared from crude extracts of S. meliloti. Activity was restored by dialysis against either MnCl(2) or Fe(NH(4))(2)(SO(4))(2), demonstrating the cambialistic nature of the S. meliloti SOD. The recovered activity with manganese was sevenfold higher than with iron. Both reconstituted enzymes were resistant to H(2)O(2). Sequence comparison with 70 FeSODs and MnSODs indicates that S. meliloti SOD contains several atypical residues at specific sites that might account for the activation by manganese and resistance to H(2)O(2) of this unusual Fe-type SOD.