The lichens <Emphasis Type="Italic">Xanthoria elegans</Emphasis> and <Emphasis Type="Italic">Cetraria islandica</Emphasis> maintain a high protection against UV-B radiation in Arctic habitats

This study reports UV screening pigments in the upper cortices of two widespread lichens collected in three sun-exposed locations along a latitudinal gradient from the Arctic lowland to alpine sites of the Central European Alps. Populations from the Alps receive 3–5 times higher UV-B irradiance than their Arctic counterparts from Svalbard because of latitudinal and altitudinal gradients in UV-B irradiance. In Cetraria islandica, the screening capacity of melanin in the upper cortices was assessed by direct measurements of cortical transmittance (250–1,000 nm). A comparison of cortical transmittances in brown sun-exposed and pale shade-adapted forest C. islandica thalli showed that fungal melanins strongly absorb both UV-B and photosynthetically active radiation (PAR). For Xanthoria elegans cortical UV-B absorbing pigments, mainly the orange parietin, were extracted and quantified. Field experiments with extracted, parietin-deficient X. elegans thalli cultivated under various filters showed that UV-B was essential for the induction of parietin synthesis. The parietin resynthesis in these parietin-deficient samples increased with decreasing latitude of their location in which they had been sampled, which may imply that the synthesis of pigments is habitat specific. However, no latitudinal gradient in cortical screening capacity was detected for any of the two species investigated in the field. This implies that Arctic populations maintain a high level of screening pigments in spite of low ambient UV-B, and that the studied lichen species presumably may tolerate an increase in UV-B radiation due to the predicted thinning of the ozone layer over polar areas     

Increased activin levels in cerebrospinal fluid of rabbits with bacterial meningitis are associated with activation of microglia

Activin, a member of the transforming growth factor superfamily, is upregulated in a number of inflammatory episodes such as septicemia and rheumatoid arthritis. In the CNS, activin has been predominantly assessed in terms of a neuroprotective role. In this report we characterized the activin response in the CNS in a rabbit model of meningitis. In normal animals, cerebrospinal fluid (CSF) activin levels were higher than those in serum, indicating an intracranial secretion of this cytokine. Following intracisternal inoculation with Streptococcus pneumoniae, activin in CSF was unchanged for the first 12 h and then rose progressively; levels were increased approximately 15-fold within 24 h. Activin levels were correlated positively with CSF protein content and with the number of apoptotic neurons in the dentate gyrus. No apparent correlation was observed between CSF activin concentrations and bacterial titer, lactate concentrations or leukocyte density. Using immunohistochemistry, activin staining was localized to epithelial cells of the choroid plexus, cortical neurons and the CA3 region of the hippocampus, with similar staining intensities in both normal and meningitic brains. However, in meningitic brains there was also strong staining in activated microglia and infiltrating macrophages. Taken together, these results demonstrate that activin forms part of the CNS response to immune challenge and may be an important mediator to modulate inflammatory processes in the brain.     

The design and discovery of novel amide CCR5 antagonists

The synthesis of a range of novel amine-containing structures and their primary potency as inhibitors of HIV-1 fusion via blocking of the CCR5 receptor is described. The development of the medicinal chemistry strategy and SAR’s which led to the identification of the piperidine amide compounds 33 and 36 as excellent leads for further evaluation is described, along with key physicochemical data which highlighted their lead potential.     

Weichselian chironomid and cladoceran assemblages from maar lakes

Sediments from maar lakes in the periglacial area were analysed to obtain information about the limnetic fauna of Pleniglacial lakes. On the basis of abundance and species composition of the subfossil chironomid and cladoceran assemblages, three major zones were biostratigraphically separated: the Upper Pleniglacial, the Middle Pleniglacial, and the Eem Interglacial.     

Evidence that humidity influences snake activity patterns: a field study of the Malayan pit viper Calloselasma rhodostoma

Multivariate statistical methods were used to elucidate which environmental factors influence the activity patterns of free-living Malayan pit vipers, Calloselasma rhodostoma. Fourteen adult snakes were implanted with miniature radiotransmitters and located a total of 887 times in 5 months. The pit vipers usually remained coiled on the ground for several consecutive days before moving at night to a new site. Partial correlation tests revealed that the frequency and distance of movements to new sites by tagged snakes were highly positively correlated with ambient relative humidity, but not with rainfall, ambient temperature or the lunar cycle. This finding was corroborated by the frequency with which active non-tagged C. rhodostoma were encountered at night, In each site, the proportion of the snakes' bodies exposed to view was positively correlated with ambient humidity, and the snakes retreated to areas with deeper undergrowth when ambient humidity was low. Overt thermoregulatory behaviour was not observed, and implanted thermosensitive transmitters revealed that the snakes were passive thermoconformers.
These findings seem lo contradict much of the current literature which shows temperature to be the dominant abiotic factor affecting reptilian activity, but most herpetologists have considered only temperate forms. Ambient temperature in our tropical study site was warm and relatively constant throughout the year (mean daily range = 24- 33°C), so the pit vipers could passively maintain body temperature within a fairly narrow range, with a daytime mean of 29.4°C. Ambient relative humidity, on the other hand, was very variable, and confining exposure and activity to periods of high ambient humidity may be necessary to avoid dehydration     

Regional Differences in Seasonal Timing of Rainfall Discriminate between Genetically Distinct East African Giraffe Taxa

Masai (Giraffa tippelskirchi), Reticulated (G. reticulata) and Rothschild''s (G. camelopardalis) giraffe lineages in East Africa are morphologically and genetically distinct, yet in Kenya their ranges abut. This raises the question of how divergence is maintained among populations of a large mammal capable of long-distance travel, and which readily hybridize in zoos. Here we test four hypotheses concerning the maintenance of the phylogeographic boundaries among the three taxa: 1) isolation-by-distance; 2) physical barriers to dispersal; 3) general habitat differences resulting in habitat segregation; or 4) regional differences in the seasonal timing of rainfall, and resultant timing of browse availability. We used satellite remotely sensed and climate data to characterize the environment at the locations of genotyped giraffes. Canonical variate analysis, random forest algorithms, and generalized dissimilarity modelling were employed in a landscape genetics framework to identify the predictor variables that best explained giraffes'' genetic divergence. We found that regional differences in the timing of precipitation, and resulting green-up associated with the abundance of browse, effectively discriminate between taxa. Local habitat conditions, topographic and human-induced barriers, and geographic distance did not aid in discriminating among lineages. Our results suggest that selection associated with regional timing of events in the annual climatic cycle may help maintain genetic and phenotypic divergence in giraffes. We discuss potential mechanisms of maintaining divergence, and suggest that synchronization of reproduction with seasonal rainfall cycles that are geographically distinct may contribute to reproductive isolation. Coordination of weaning with green-up cycles could minimize the costs of lactation and predation on the young. Our findings are consistent with theory and empirical results demonstrating the efficacy of seasonal or phenologically dictated selection pressures in contributing to the reproductive isolation of parapatric populations.     

Opening windows into the cell: focused-ion-beam milling for cryo-electron tomography

1. Download : Download high-res image (251KB)
2. Download : Download full-size image

     

Rapid self-assembly of alpha-synuclein observed by in situ atomic force microscopy

Self-assembly of alpha-synuclein resulting in protein aggregates of diverse morphology has been implicated in the pathogenesis of Parkinson's disease and other neurodegenerative disorders known as synucleinopathies. Apart from its biomedical relevance, this aggregation process is representative of the interconversion of an unfolded protein into nanostructures with typical amyloid features. We have used in situ tapping mode atomic force microscopy to continuously monitor the self-assembly of wild-type alpha-synuclein, its disease-related mutants A30P and A53T, and the C-terminally truncated variant alpha-synuclein(1-108). Different aggregation modes were observed depending on experimental conditions, i.e. pH, protein concentration, polyamine concentration, temperature and the supporting substrate. At pH 7.5, in the absence of the biogenic polyamines spermidine or spermine, elongated sheets 1.1(+/-0.2)nm in height and presumably representing individual beta-sheet structures, were formed on mica substrates within a few minutes. Their orientation was directed by the crystalline substructure of the substrate. In contrast, sheet formation was not observed with hydrophobic highly oriented pyrolytic graphite substrates, suggesting that negatively charged surfaces promote alpha-synuclein self-assembly. In the presence of spermidine or spermine 5.9(+/-1.0)nm high spheroidal structures were preferentially formed, sharing characteristics with similar structures previously reported for several amyloidogenic proteins and linked to neurotoxicity. alpha-Synuclein spheroid formation depended critically on polyamine binding to the C terminus, revealing a promoting effect of the C terminus on alpha-synuclein assembly in the bound state. In rare cases, fibril growth from spheroids or preformed aggregates was observed. At pH 5.0, fibrils were formed initially and incorporated into amorphous aggregates in the course of the aggregation process, providing evidence for the potential of amyloid fibril surfaces to act as nucleation sites in amorphous aggregation. This study provides a direct insight into different modes of alpha-synuclein self-assembly and identifies key factors modulating the aggregation process.     

cGMP/Protein Kinase G Signaling Suppresses Inositol 1,4,5-Trisphosphate Receptor Phosphorylation and Promotes Endoplasmic Reticulum Stress in Photoreceptors of Cyclic Nucleotide-gated Channel-deficient Mice

Photoreceptor cyclic nucleotide-gated (CNG) channels play a pivotal role in phototransduction. Mutations in the cone CNG channel subunits CNGA3 and CNGB3 are associated with achromatopsia and cone dystrophies. We have shown endoplasmic reticulum (ER) stress-associated apoptotic cone death and increased phosphorylation of the ER Ca²⁺ channel inositol 1,4,5-trisphosphate receptor 1 (IP₃R1) in CNG channel-deficient mice. We also presented a remarkable elevation of cGMP and an increased activity of the cGMP-dependent protein kinase (protein kinase G, PKG) in CNG channel deficiency. This work investigated whether cGMP/PKG signaling regulates ER stress and IP₃R1 phosphorylation in CNG channel-deficient cones. Treatment with PKG inhibitor and deletion of guanylate cyclase-1 (GC1), the enzyme producing cGMP in cones, were used to suppress cGMP/PKG signaling in cone-dominant Cnga3^−/−/Nrl^−/− mice. We found that treatment with PKG inhibitor or deletion of GC1 effectively reduced apoptotic cone death, increased expression levels of cone proteins, and decreased activation of Müller glial cells. Furthermore, we observed significantly increased phosphorylation of IP₃R1 and reduced ER stress. Our findings demonstrate a role of cGMP/PKG signaling in ER stress and ER Ca²⁺ channel regulation and provide insights into the mechanism of cone degeneration in CNG channel deficiency.