Phenology, distribution, and host specificity of Solenopsis invicta virus-1

Studies were conducted to examine the phenology, geographic distribution, and host specificity of the Solenopsis invicta virus-1 (SINV-1). Two genotypes examined, SINV-1 and -1A, exhibited similar seasonal prevalence patterns. Infection rates among colonies of S. invicta in Gainesville, Florida, were lowest from early winter (December) to early spring (April) increasing rapidly in late spring (May) and remaining high through August before declining again in the fall (September/October). Correlation analysis revealed a significant relationship between mean monthly temperature and SINV-1 (p<0.0005, r=0.82) and SINV-1A (p<0.0001, r=0.86) infection rates in S. invicta colonies. SINV-1 was widely distributed among S. invicta populations. The virus was detected in S. invicta from Argentina and from all U.S. states examined, with the exception of New Mexico. SINV-1 and -1A were also detected in other Solenopsis species. SINV-1 was detected in Solenopsis richteri and the S. invicta/richteri hybrid collected from northern Alabama and Solenopsis geminata from Florida. SINV-1A was detected in S. geminata and Solenopsis carolinensis in Florida and the S. invicta/richteri hybrid in Alabama. Of the 1989 arthropods collected from 6 pitfall trap experiments from Gainesville and Williston, Florida, none except S. invicta tested positive for SINV-1 or SINV-1A. SINV-1 did not appear to infect or replicate within Sf9 or Dm-2 cells in vitro. The number of SINV-1 genome copies did not significantly increase over the course of the experiment, nor were any cytopathic effects observed. Phylogenetic analyses of SINV-1/-1A nucleotide sequences indicated significant divergence between viruses collected from Argentina and the U.S.     

The calcium-binding C-terminal domain of Escherichia coli alpha-hemolysin is a major determinant in the surface-active properties of the protein

alpha-Hemolysin (HlyA) from Escherichia coli is a protein toxin (1024 amino acids) that targets eukaryotic cell membranes, causing loss of the permeability barrier. HlyA consists of two main regions, an N-terminal domain rich in amphipathic helices, and a C-terminal Ca(2+)-binding domain containing a Gly- and Asp-rich nonapeptide repeated in tandem 11-17 times. The latter is called the RTX domain and gives its name to the RTX protein family. It had been commonly assumed that membrane interaction occurred mainly if not exclusively through the amphipathic helix domain. However, we have cloned and expressed the C-terminal region of HlyA, containing the RTX domain plus a few stabilizing sequences, and found that it is a potent surface-active molecule. The isolated domain binds Ca(2+) with about the same affinity (apparent K(0.5) approximately 150 microM) as the parent protein HlyA, and Ca(2+) binding induces in turn a more compact folding with an increased proportion of beta-sheet structure. Both with and without Ca(2+) the C-terminal region of HlyA can interact with lipid monolayers spread at an air-water interface. However, the C-terminal domain by itself is devoid of membrane lytic properties. The present results can be interpreted in the light of our previous studies that involved in receptor binding a peptide in the C-terminal region of HlyA. We had also shown experimentally the distinction between reversible membrane adsorption and irreversible lytic insertion of the toxin. In this context, the present data allow us to propose that both major domains of HlyA are directly involved in membrane-toxin interaction, the nonapeptide repeat, calcium-binding RTX domain being responsible for the early stages of HlyA docking to the target membrane.     

Road crossing in bank voles and yellow-necked mice

Roads and highways represent one of the most important anthropogenic impacts on natural areas and contribute to habitat fragmentation, because they are linear features that can inhibit animal movement, thereby causing barrier effects subdividing the populations adjacent to the roads. The paper examines to what extent a narrow (2-lane) and a wide (4-lane) highways represent barriers for two small mammal species: bank volesClethrionomys glareolus Schreber, 1780 and yellow-necked miceApodemus flavicollis Melchior, 1834, and whether displaced rodents are able to return across roads of different widths. The study was performed at four sites in the Czech Republic. The capture-mark-recapture method was used to determine crossing rates. At two sites, the animals captured close to the road were transferred to the other side and released, to compare return movements across the roads with the movements made by the non-transferred animals. We found that the narrow highway did not prevent movement of neither of the species, although voles crossed only after they had been transferred. Wide highways, on the other hand, completely prevened crossing of both species. While the narrow highways acted at individuals level, the wide highways affected the population subvision.     

Description of Tischeria gouaniae sp. n. from the tropical forest of Belize - an exotic new addition to the American fauna of Tischeria (Insecta: Lepidoptera: Tischeriidae)

We describe Tischeria gouaniae sp. n. from the tropical forests of Belize. The new species is a leaf-miner of Gouania polygama (Rhamnaceae). Together with the related T. bifurcata Braun, it is among the most striking representatives of Tischeria. Both species possess a pseudognathos and very broad aedeagus fused with extremely long lateral processes of the juxta. The new species differs from T. bifurcata in the broadly rounded vinculum, spiny juxta, and slender apical processes of the aedeagus, and in its host plant. The external features and male genitalia of Tischeria gouaniae sp. n. are figured and described. A checklist and distribution map for all nine currently known Tischeria species from North and South America are given. Most American species are known from USA, but others are now known from tropical forest habitats of Central America, the Caribbean, and Guyana. Host-plants are known for five of the nine species reviewed here, belonging to four genera and two plant families (Fagaceae and Rhamnaceae).     

Expression of Hoxa2 in cells entering chondrogenesis impairs overall cartilage development

Vertebrate Hox genes act as developmental architects by patterning embryonic structures like axial skeletal elements, limbs, brainstem territories, or neural crest derivatives. While active during the patterning steps of development, these genes turn out to be down-regulated in specific differentiation programs like that leading to chondrogenesis. To investigate why chondrocyte differentiation is correlated to the silencing of a Hox gene, we generated transgenic mice allowing Cre-mediated conditional misexpression of Hoxa2 and induced this gene in Collagen 2 alpha 1-expressing cells committed to enter chondrogenesis. Persistent Hoxa2 expression in chondrogenic cells resulted in overall chondrodysplasia with delayed cartilage hypertrophy, mineralization, and ossification but without proliferation defects. The absence of skeletal patterning anomaly and the regular migration of precursor cells indicated that the condensation step of chondrogenesis was normal. In contrast, closer examination at the differentiation step showed severely impaired chondrocyte differentiation. In addition, this inhibition affected structures independently of their embryonic origin. In conclusion, for the first time here, by a cell-type specific misexpression, we precisely uncoupled the patterning function of Hoxa2 from its involvement in regulating differentiation programs per se and demonstrate that Hoxa2 displays an anti-chondrogenic activity that is distinct from its patterning function.     

H-mediated coupling of transmembrane Ca fluxes in vegetative Trichoderma viride mycelia suggested by the study of ageing and adaptation to extreme Ca concentrations

The adaptation to extreme concentrations of Ca²⁺ and its consequence on the properties of the ⁴⁵Ca²⁺ transport were studied in submerged mycelia of Trichoderma viride. The adaptation to low [Ca²⁺]_o did not cause changes in kinetic parameters of the ⁴⁵Ca²⁺ influx but the adaptation to high [Ca²⁺]_o increased the K_M(Ca2+). The V_max of the ⁴⁵Ca²⁺ influx decreased with the age of (non-adapted) mycelia with concomitant decrease of the K_M(Ca2+) these changes were prevented in mycelia adapted to high Ca²⁺. High [Ca²⁺]_o decreased the stimulation by the uncoupler, 3, 3′, 4′, 5-tetrachloro salicylanilide (TCS) (30 μM), as compared to the control, whereas the Ca²⁺ chelator, EGTA, stimulated it. In the aged mycelia, the stimulation by TCS of the ⁴⁵Ca²⁺ influx faded away, in parallel with the activity of the H⁺-ATPase. The ⁴⁵Ca²⁺ efflux from mycelia was affected by TCS in a similar way as the ⁴⁵Ca²⁺ influx. The results demonstrate the adaptive responses of transport processes participating in the mycelial Ca²⁺ homeostasis and ageing are in agreement with a notion that both Ca²⁺-influx and-efflux are coupled by the H⁺-homeostasis at the plasma membrane.