Analysis of Amblyomma sculptum haplotypes in an area endemic for Brazilian spotted fever

Amblyomma sculptum (Ixodida: Ixodidae) Berlese, 1888, a member of the Amblyomma cajennense complex, is the major vector of Brazilian spotted fever (BSF) in southeastern Brazil. In this study, the genetic diversity of A. sculptum populations in the state of Rio de Janeiro (RJ), Brazil, was investigated because genetic variability in tick populations may be related to vector competence. Samples of A. sculptum from 19 municipalities in 7 regions of RJ were subjected to DNA extraction, amplification and sequencing of D‐loop, cytochrome oxidase II and 12S rDNA mitochondrial genes. These sequences were used to map the genetic diversity of this tick. Amblyomma sculptum populations are genetically diverse in RJ, especially in the South Centre and Highland regions. Few unique haplotypes were observed in all populations, and the majority of genetic variation found was among ticks within each population. Phylogenetic reconstruction reinforced the assumption that all the haplotypes identified in RJ belong to A. sculptum. However, some RJ haplotypes are closer to A. sculptum from Argentina than to A. sculptum from elsewhere in Brazil. In RJ, A. sculptum has high genetic diversity, although little genetic differentiation. Observations also indicated a high level of gene flow among the studied populations and no evidence of population structure according to region in RJ.     

我国巴拉巴按蚊形态描述

白踝按蚊种团是由很多形态近似的蚊种组成,其中巴拉巴按蚊和白踝按蚊均为东南亚一带的重要传疟媒介。我国过去资料均记载为白踝按蚊,但未从形态上详细鉴定。为了确定该种的分类地位,1963年作者等在海南岛万宁县兴隆附近山林区采集“白踝按蚊”全套标本10批共150多套,1971年后从云南省采集少数标本进行形态鉴定,发现其与Colless(1956,1957)所描述的白踝按蚊Anopheles leucosphyrus leucosphyrus Donitz(1901)有很明显的差别,而与巴拉巴按蚊A.balabacensis balabacensis Balsas(1936)除某些特征略有差异外,余均完全一致。按Colless的分类法,过去我国记载的“白踝按蚊”,应鉴定为巴拉巴按蚊A.balabacensis balabacensis Baisas。     

Evolutionary origins of Brassicaceae specific genes in Arabidopsis thaliana

Background  

All sequenced genomes contain a proportion of lineage-specific genes, which exhibit no sequence similarity to any genes outside the lineage. Despite their prevalence, the origins and functions of most lineage-specific genes remain largely unknown. As more genomes are sequenced opportunities for understanding evolutionary origins and functions of lineage-specific genes are increasing.     

Evolution of anaerobic ciliates from the gastrointestinal tract: phylogenetic analysis of the ribosomal repeat from Nyctotherus ovalis and its relatives

The 18S and 5.8S rDNA genes and the internal transcribed spacers ITS-1 and ITS-2 of ciliates living in the hindgut of frogs, millipedes, and cockroaches were analyzed in order to study the evolution of intestinal protists. All ciliates studied here belong to the genus Nycrotherus. Phylogenetic analysis revealed that these ciliates from a monophyletic group that includes the distantly related anaerobic free-living heterotrichous ciliates Metopus palaeformis and Metopus contortus. The intestinal ciliates from the different vertebrate and invertebrate hosts are clearly divergent at the level of their rDNA repeats. This argues for the antiquity of the associations and a predominantly vertical transmission. This mode of transmission seems to be controlled primarily by the behavior of the host. The different degrees of divergence between ciliates living in different strains of one and the same cockroach species most likely reflect the different geographical origins of the hosts. In addition, host switches must have occurred during the evolution of cockroaches, since identical ciliates were found only in distantly related hosts. These phenomena prevent the reconstruction of potential cospeciation events.      

Oblique membrane insertion of viral fusion peptide probed by neutron diffraction

Fusion peptides mimic the membrane fusion activities of the larger viral proteins from which they derive their sequences. A possible mode of activity involves their oblique insertion into lipid bilayers, causing membrane disruption by promoting highly curved hemifusion intermediates, leading to fusion. We have determined the location and orientation of the simian immunodeficiency virus (SIV) fusion peptide in planar lipid bilayers using neutron lamellar diffraction. The helical axis of the peptide adopts an angle of 55 degrees relative to the membrane normal, while it positions itself nearest the lipid bilayer surface. This is the first direct observation of the structural interaction between a fusion peptide and a phospholipid bilayer.     

Experimental evidence for hydrophobic matching and membrane-mediated interactions in lipid bilayers containing gramicidin.

Hydrophobic matching, in which transmembrane proteins cause the surrounding lipid bilayer to adjust its hydrocarbon thickness to match the length of the hydrophobic surface of the protein, is a commonly accepted idea in membrane biophysics. To test this idea, gramicidin (gD) was embedded in 1, 2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) and 1, 2-myristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers at the peptide/lipid molar ratio of 1:10. Circular dichroism (CD) was measured to ensure that the gramicidin was in the beta6.3 helix form. The bilayer thickness (the phosphate-to-phosphate distance, or PtP) was measured by x-ray lamellar diffraction. In the Lalpha phase near full hydration, PtP is 30.8 A for pure DLPC, 32.1 A for the DLPC/gD mixture, 35.3 A for pure DMPC, and 32.7 A for the DMPC/gD mixture. Gramicidin apparently stretches DLPC and thins DMPC toward a common thickness as expected by hydrophobic matching. Concurrently, gramicidin-gramicidin correlations were measured by x-ray in-plane scattering. In the fluid phase, the gramicidin-gramicidin nearest-neighbor separation is 26.8 A in DLPC, but shortens to 23.3 A in DMPC. These experiments confirm the conjecture that when proteins are embedded in a membrane, hydrophobic matching creates a strain field in the lipid bilayer that in turn gives rise to a membrane-mediated attractive potential between proteins.     

Theoretical analysis of hydrophobic matching and membrane-mediated interactions in lipid bilayers containing gramicidin.

We present a quantitative analysis of the effects of hydrophobic matching and membrane-mediated protein-protein interactions exhibited by gramicidin embedded in dimyristoylphosphatidylcholine (DMPC) and dilauroylphosphatidylcholine (DLPC) bilayers (Harroun et al., 1999. Biophys. J. 76:937-945). Incorporating gramicidin, at 1:10 peptide/lipid molar ratio, decreases the phosphate-to-phosphate (PtP) peak separation in the DMPC bilayer from 35.3 A without gramicidin to 32.7 A. In contrast, the same molar ratio of gramicidin in DLPC increases the PtP from 30.8 A to 32.1 A. Concurrently, x-ray in-plane scattering showed that the most probable nearest-neighbor separation between gramicidin channels was 26.8 A in DLPC, but reduced to 23.3 A in DMPC. In this paper we review the idea of hydrophobic matching in which the lipid bilayer deforms to match the hydrophobic surface of the embedded proteins. We use a simple elasticity theory, including thickness compression, tension, and splay terms to describe the membrane deformation. The energy of membrane deformation is compared with the energy cost of hydrophobic mismatch. We discuss the boundary conditions between a gramicidin channel and the lipid bilayer. We used a numerical method to solve the problem of membrane deformation profile in the presence of a high density of gramicidin channels and ran computer simulations of 81 gramicidin channels to find the equilibrium distributions of the channels in the plane of the bilayer. The simulations contain four parameters: bilayer thickness compressibility 1/B, bilayer bending rigidity Kc, the channel-bilayer mismatch Do, and the slope of the interface at the lipid-protein boundary s. B, Kc, and Do were experimentally measured; the only free parameter is s. The value of s is determined by the requirement that the theory produces the experimental values of bilayer thinning by gramicidin and the shift in the peak position of the in-plane scattering due to membrane-mediated channel-channel interactions. We show that both hydrophobic matching and membrane-mediated interactions can be understood by the simple elasticity theory.     

The oxygen delivery response to acute hypoxia during incremental knee extension exercise differs in active and trained males

Background

It is well known that hypoxic exercise in healthy individuals increases limb blood flow, leg oxygen extraction and limb vascular conductance during knee extension exercise. However, the effect of hypoxia on cardiac output, and total vascular conductance is less clear. Furthermore, the oxygen delivery response to hypoxic exercise in well trained individuals is not well known. Therefore our aim was to determine the cardiac output (Doppler echocardiography), vascular conductance, limb blood flow (Doppler echocardiography) and muscle oxygenation response during hypoxic knee extension in normally active and endurance-trained males.

Methods

Ten normally active and nine endurance-trained males (VO_2max = 46.1 and 65.5 mL/kg/min, respectively) performed 2 leg knee extension at 25, 50, 75 and 100% of their maximum intensity in both normoxic and hypoxic conditions (FIO₂ = 15%; randomized order). Results were analyzed with a 2-way mixed model ANOVA (group × intensity).

Results

The main finding was that in normally active individuals hypoxic sub-maximal exercise (25 – 75% of maximum intensity) brought about a 3 fold increase in limb blood flow but decreased stroke volume compared to normoxia. In the trained group there were no significant changes in stroke volume, cardiac output and limb blood flow at sub-maximal intensities (compared to normoxia). During maximal intensity hypoxic exercise limb blood flow increased approximately 300 mL/min compared to maximal intensity normoxic exercise.

Conclusion

Cardiorespiratory fitness likely influences the oxygen delivery response to hypoxic exercise both at a systemic and limb level. The increase in limb blood flow during maximal exercise in hypoxia (both active and trained individuals) suggests a hypoxic stimulus that is not present in normoxic conditions.