Herbivory on invasive exotic plants and their non-invasive relatives

The Enemy Release Hypothesis links exotic plant success to escape from enemies such as herbivores and pathogens. Recent work has shown that exotic plants that more fully escape herbivores and pathogens are more likely to become highly invasive, compared to plants with higher enemy loads in their novel ranges. We predicted that highly invasive plants from the Asteraceae and the Brassicaceae would be less acceptable, in laboratory no-choice feeding trials, to the generalist herbivore the American grasshopper, Schistocerca americana. We also compared herbivory on invasive and non-invasive plants from the genus Centaurea in no-choice feeding trials using the red-legged grasshopper Melanoplus femurrubrum and in a common garden in the field. In accordance with our predictions, highly invasive plants were fed on less by grasshoppers in the laboratory. They also received less damage in the field, suggesting that they contain feeding deterrents that render them less acceptable to generalist herbivores than non-invasive plants.     

Influence of age and exercise training on lipid metabolism in Fischer-344 rats

The influence of training on fatty acid and glyceride synthesis by liver and adipose tissue homogenates of young and old Fischer-344 rats was examined. Four groups of rats (10 animals/group) were studied: young untrained, young trained, old untrained, and old trained. Training of each group was for 10 wk at 75% maximal O2 uptake. Young rats were killed at 6 mo of age and old rats were killed at 27 mo of age. Fatty acid synthesis was assessed by measuring the activities of acetyl-CoA carboxylase, fatty acid synthase, ATP citrate-lyase, "malic" enzyme, and glucose-6-phosphate dehydrogenase. Glyceride synthesis was evaluated by determining the rate of incorporation of [14C]glycerol 3-phosphate into lipids. In addition, lipoprotein lipase activity was measured in acetone-ether powders of adipose tissue from the four groups of rats. In liver, training had no effect on fatty acid or glyceride synthesis in either group. However, aging caused a significant decrease in the activities of four of the lipogenic enzymes but had no effect on glyceride synthesis. Training caused an increase in fatty acid synthase and glyceride synthesis in adipose tissue, and aging decreased lipoprotein lipase activity. It was concluded that training enhances the synthetic capacity of lipids by adipose tissue but that aging had a more profound effect in that the activities of the enzymes involved in these processes were lower in the old rats. Furthermore, the decreased activity of lipoprotein lipase in the older rats may explain the higher plasma triglyceride levels that were observed in these animals.     

Influence of attractants and repellents on methyl group turnover on methyl-accepting chemotaxis proteins of Bacillus subtilis and role of CheW.

The ability of attractants and repellents to affect the turnover of methyl groups on the methyl-accepting chemotaxis proteins (MCPs) was examined for Bacillus subtilis. Attractants were found to cause an increase in the turnover of methyl groups esterified to the MCPs, while repellents caused a decrease. These reactions do not require CheW. However, a cheW null mutant exhibits enhanced turnover in unstimulated cells. Assuming that the turnover of methyl groups on the MCPs reflects a change in the activity of CheA, these results suggest that the activation of CheA via chemoeffector binding at the receptor does not require CheW.     

Temperature-dependent perturbation of phospholipid bilayers by dimethylsulfoxide.

Dimethylsulfoxide (DMSO) is known to protect isolated enzymes during freezing while destabilizing proteins at high temperatures. This apparent paradox is the subject of a review by Arakawa et al. ((1990) Cryobiology 27, 401-415), who present evidence for a temperature-dependent, hydrophobic interaction between DMSO and non-polar moieties of proteins. The present study investigates the interaction of DMSO with phospholipid bilayers. Phospholipid vesicles containing carboxyfluorescein were exposed to several concentrations of DMSO at various temperatures. Leakage rates increased with DMSO concentration and temperature. This effect was not reduced in the presence of solutes that have been shown to neutralize DMSO toxicity in tissues. The increased leakage rates correlate well with the increased partitioning of DMSO from water to octanol at higher temperatures. Additionally, reductions in the CH2 vibrations of the bilayer are also shown to depend on DMSO concentration and temperature. A similar reduction in CH2 vibrations was observed in solutions of octanol and DMSO, suggesting that this effect is not mediated through an interaction with water. Furthermore, investigation of sulfoxide vibrations indicate that DMSO is not hydrogen bonded to the alcohol moiety of octanol, and therefore the interaction between DMSO and octanol is most likely due to a hydrophobic association. These results are consistent with a destabilization of phospholipid membranes at higher temperatures due to a hydrophobic association between DMSO and the bilayer.     

VEGF is crucial for the hepatic vascular development required for lipoprotein uptake

Hepatic lipid catabolism begins with the transport of lipoprotein remnants from the sinusoidal vasculature into hepatocytes by endocytosis via microvilli. To test the hypothesis that fenestrated sinusoidal endothelial cells (SECs) are crucial for this process, we selectively disrupted SECs by downregulating vascular endothelial growth factor (VEGF) signaling, using hepatocyte-specific, tetracycline-regulatable expression of a VEGF receptor that can sequester VEGF but cannot relay its signal. Newborn mutant livers appeared grossly normal, but displayed a dark-red color that was distinguishable from normal physiological lipid-rich pink livers. Mutant sinusoidal networks were reduced and their SECs lacked fenestrae. Hepatocellular lipid levels were profoundly reduced, as determined by Oil Red O staining and transmission electron microscopy, and fewer hepatocytic microvilli were evident, indicating impaired lipoprotein endocytosis. Levels of apolipoprotein (APO) E bound to mutant sinusoidal networks were significantly reduced, and fluorescently-labeled murine remnant lipoproteins injected into the blood stream failed to accumulate in the space of Disse and diffuse into hepatocytes, providing evidence that reduced hepatocellular lipid levels in mutant livers are due to impaired lipoprotein uptake. Temporal downregulation of VEGF signaling revealed that it is crucial at all developmental stages of hepatic vascular morphogenesis, and repression of the dominant-negative effect can rescue the phenotype. These findings provide the first genetic evidence that VEGF dynamically regulates SEC fenestration during liver organogenesis, a process that is required for lipoprotein uptake by the liver.     

Concomitant Raman spectroscopy and dynamic light scattering for characterization of therapeutic proteins at high concentrations

A Raman spectrometer and dynamic light scattering system were combined in a single platform (Raman–DLS) to provide concomitant higher order structural and hydrodynamic size data for therapeutic proteins at high concentration. As model therapeutic proteins, we studied human serum albumin (HSA) and intravenous immunoglobulin (IVIG). HSA concentration and temperature interval during heating did not affect the onset temperatures for conformation perturbation or aggregation. The impact of pH on thermal stability of HSA was tested at pHs 3, 5, and 8. Stability was the greatest at pH 8, but distinct unfolding and aggregation behaviors were observed at the different pHs. HSA structural transitions and aggregation kinetics were also studied in real time during isothermal incubations at pH 7. In a forced oxidation study, it was found that hydrogen peroxide (H₂O₂) treatment reduced the thermal stability of HSA. Finally, the structure and thermal stability of IVIG were studied, and a comprehensive characterization of heating-induced structural perturbations and aggregation was obtained. In conclusion, by providing comprehensive data on protein tertiary and secondary structures and hydrodynamic size during real-time heating or isothermal incubation experiments, the Raman–DLS system offers unique physical insights into the properties of high-concentration protein samples.     

Genetic and phylogenetic divergence of feline immunodeficiency virus in the puma (Puma concolor).

Feline immunodeficiency virus (FIV) is a lentivirus which causes an AIDS-like disease in domestic cats (Felis catus). A number of other felid species, including the puma (Puma concolor), carry a virus closely related to domestic cat FIV. Serological testing revealed the presence of antibodies to FIV in 22% of 434 samples from throughout the geographic range of the puma. FIV-Pco pol gene sequences isolated from pumas revealed extensive sequence diversity, greater than has been documented in the domestic cat. The puma sequences formed two highly divergent groups, analogous to the clades which have been defined for domestic cat and lion (Panthera leo) FIV. The puma clade A was made up of samples from Florida and California, whereas clade B consisted of samples from other parts of North America, Central America, and Brazil. The difference between these two groups was as great as that reported among three lion FIV clades. Within puma clades, sequence variation is large, comparable to between-clade differences seen for domestic cat clades, allowing recognition of 15 phylogenetic lineages (subclades) among puma FIV-Pco. Large sequence divergence among isolates, nearly complete species monophyly, and widespread geographic distribution suggest that FIV-Pco has evolved within the puma species for a long period. The sequence data provided evidence for vertical transmission of FIV-Pco from mothers to their kittens, for coinfection of individuals by two different viral strains, and for cross-species transmission of FIV from a domestic cat to a puma. These factors may all be important for understanding the epidemiology and natural history of FIV in the puma.     

Intertissue differences in the hysteretic behaviour of carnitine palmitoyltransferase in the presence of malonyl-CoA.

In the presence of malonyl-CoA, the overt form of carnitine palmitoyltransferase (CPT1) in mitochondria from rat liver, kidney cortex, heart, skeletal muscle and brown adipose tissue shows non-linear time courses, suggesting hysteretic behaviour. The pattern of this hysteresis is similar in heart, skeletal muscle and brown adipose tissue, but the hysteretic behaviour of the enzyme in these three tissues differs markedly from that seen in liver and kidney.     

Accurate measurement of gene copy number for human alpha-defensin DEFA1A3

Background

Multi-allelic copy number variants include examples of extensive variation between individuals in the copy number of important genes, most notably genes involved in immune function. The definition of this variation, and analysis of its impact on function, has been hampered by the technical difficulty of large-scale but accurate typing of genomic copy number. The copy-variable alpha-defensin locus DEFA1A3 on human chromosome 8 commonly varies between 4 and 10 copies per diploid genome, and presents considerable challenges for accurate high-throughput typing.

Results

In this study, we developed two paralogue ratio tests and three allelic ratio measurements that, in combination, provide an accurate and scalable method for measurement of DEFA1A3 gene number. We combined information from different measurements in a maximum-likelihood framework which suggests that most samples can be assigned to an integer copy number with high confidence, and applied it to typing 589 unrelated European DNA samples. Typing the members of three-generation pedigrees provided further reassurance that correct integer copy numbers had been assigned. Our results have allowed us to discover that the SNP rs4300027 is strongly associated with DEFA1A3 gene copy number in European samples.

Conclusions

We have developed an accurate and robust method for measurement of DEFA1A3 copy number. Interrogation of rs4300027 and associated SNPs in Genome-Wide Association Study SNP data provides no evidence that alpha-defensin copy number is a strong risk factor for phenotypes such as Crohn’s disease, type I diabetes, HIV progression and multiple sclerosis.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-14-719) contains supplementary material, which is available to authorized users.