Aquatic invertebrate fauna of a northern prairie stream: range extensions and water quality characteristics

The benthic macroinvertebrate fauna of southern Saskatchewan, Canada, has received little attention relative to other regions of western North America. Therefore, little is known of the related aquatic ecosystem health and biogeography of regional aquatic insects. Here we present the results of an aquatic macroinvertebrate survey for the Pipestone Creek watershed in southeastern Saskatchewan. We qualitatively sampled aquatic macroinvertebrates in 5 sites on 4 dates through spring, summer, and fall 2006. Sampling produced 294 taxa of macroinvertebrates including 25 provincial range extensions to the southeast corner of the province. Presence/absence data of taxa grouped the sites into lentic and lotic sites. However, the relative proportions of the taxa varied greatly among sites, with no 2 sites having a community similarity greater than 50%. Functional feeding group analyses separated the sites into collector-dominated and scraper/grazer-dominated sites. However, the taxonomic make-up of the feeding groups varied among sites and also among dates. A modified Hilsenhoff Biotic Index of the site communities indicated that all were influenced by organic pollution. Results of this study suggest that although the watershed is enormously diverse, its biological communities are likely influenced by organic pollution. Further, range expansions of species found here, such as the stonefly Perlesta placida , have implications for invasion pathways and post-glaciation species islands in a prairie landscape.     

Mars' volatile and climate history.

There is substantial evidence that the martian volatile inventory and climate have changed markedly throughout the planet's history. Clues come from areas as disparate as the history and properties of the deep interior, the composition of the crust and regolith, the morphology of the surface, composition of the present-day atmosphere, and the nature of the interactions between the upper atmosphere and the solar wind. We piece together the relevant observations into a coherent view of the evolution of the martian climate, focusing in particular on the observations that provide the strongest constraints.     

Cooperative tandem binding of met repressor of Escherichia coli

We present biochemical and genetic data to support the hypothesis that the Escherichia coli met repressor, MetJ, binds to synthetic and natural operator sequences in tandem arrays such that repression depends not only on the affinity of the DNA-protein interaction, but also on protein-protein contacts along the tandem array. This represents a novel form of regulatory switch. Furthermore, there seems to be homology between the organization of the met and trp operators.     

Integrin cytoplasmic tyrosine motif is required for outside-in alphaIIbbeta3 signalling and platelet function.

Integrins not only bind adhesive ligands, they also act as signalling receptors. Both functions allow the integrin alphaIIbbeta3 to mediate platelet aggregation. Platelet agonists activate alphaIIbbeta3 (inside-out signalling) to allow the binding of soluble fibrinogen. Subsequent platelet aggregation leads to outside-in alphaIIbbeta3 signalling, which results in calcium mobilization, tyrosine phosphorylation of numerous proteins including beta3 itself, increased cytoskeletal reorganisation and further activation of alphaIIbbeta3. Thus, outside-in signals enhance aggregation, although the mechanisms and functional consequences of specific signalling events remain unclear. Here we describe a mouse that expresses an alphaIIbbeta3 in which the tyrosines in the integrin cytoplasmic tyrosine motif have been mutated to phenylalanines. These mice are selectively impaired in outside-in alphaIIbbeta3 signalling, with defective aggregation and clot-retraction responses in vitro, and an in vivo bleeding defect which is characterized by a pronounced tendency to rebleed. These data provide evidence for an important role of outside-in signalling in platelet physiology. Furthermore, they identify the integrin cytoplasmic tyrosine motif as a key mediator of beta-integrin signals and a potential target for new therapeutic agents.     

Charybdotoxin, a protein inhibitor of single Ca2+-activated K+ channels from mammalian skeletal muscle

The recent development of techniques for recording currents through single ionic channels has led to the identification of a K+-specific channel that is activated by cytoplasmic Ca2+. The channel has complex properties, being activated by depolarizing voltages and having a voltage-sensitivity that is modulated by cytoplasmic Ca2+ levels. The conduction behaviour of the channel is also unusual, its high ionic selectivity being displayed simultaneously with a very high unitary conductance. Very little is known about the biochemistry of this channel, largely due to the lack of a suitable ligand for use as a biochemical probe for the channel. We describe here a protein inhibitor of single Ca2+-activated K+ channels of mammalian skeletal muscle. This inhibitor, a minor component of the venom of the Israeli scorpion, Leiurus quinquestriatus, reversibly blocks the large Ca2+-activated K+ channel in a simple biomolecular reaction. We have partially purified the active component, a basic protein of relative molecular mass (Mr) approximately 7,000.     

Human immunodeficiency virus genetic variation that can escape cytotoxic T cell recognition.

In a longitudinal study of HIV seropositive patients, there were fluctuations in the specificity of cytotoxic T cells for the virus. This was matched by variability in proviral gag DNA epitope sequences in the lymphocytes of these patients. Some of these viral variants are not recognized by autologous T cells. Accumulation of such mutations in T-cell antigenic targets would provide a mechanism for immune escape.