How radiation influences atherosclerotic plaque development: a biophysical approach in ApoE ¯/¯ mice

Atherosclerosis is the development of lipid-laden plaques in arteries and is nowadays considered as an inflammatory disease. It has been shown that high doses of ionizing radiation, as used in radiotherapy, can increase the risk of development or progression of atherosclerosis. To elucidate the effects of radiation on atherosclerosis, we propose a mathematical model to describe radiation-promoted plaque development. This model distinguishes itself from other models by combining plaque initiation and plaque growth, and by incorporating information from biological experiments. It is based on two consecutive processes: a probabilistic dose-dependent plaque initiation process, followed by deterministic plaque growth. As a proof of principle, experimental plaque size data from carotid arteries from irradiated ApoE\(^{{-/-}}\) mice was used to illustrate how this model can provide insight into the underlying biological processes. This analysis supports the promoting role for radiation in plaque initiation, but the model can easily be extended to include dose-related effects on plaque growth if available experimental data would point in that direction. Moreover, the model could assist in designing future biological experiments on this research topic. Additional biological data such as plaque size data from chronically-irradiated mice or experimental data sets with a larger variety in biological parameters can help to further unravel the influence of radiation on plaque development. To the authors’ knowledge, this is the first biophysical model that combines probabilistic and mechanistic modeling which uses experimental data to investigate the influence of radiation on plaque development.     

Still life: Pollen tube growth observed in millisecond resolution

Our recent work used novel methods to localize and track discrete vesicle populations in pollen tubes undergoing oscillatory growth. The results show that clathrin-dependent endocytosis occurs along the shank of the pollen tube, smooth vesicle endocytosis occurs at the tip, and exocytosis occurs in the subapical region. Here, growth of tobacco and lily pollen tubes is examined in greater temporal resolution using refraction-free high-resolution time-lapse differential interference contrast microscopy. Images were collected at 0.21 s intervals for 10 min, sequentially examined for millisecond details, compressed into video format and then examined for details of growth dynamics. The subapical growth zone is structurally fluid, with vesicle insertion into the plasma membrane, construction of new cell surface and cellular expansion. Incorporation of new membrane and wall materials causes localized disruption at the cell surface that precedes the start of the growth cycle by 3.44 ± 0.39 s in tobacco, and 1.02 ± 0.01 s in lily pollen tubes. Vesicle deposition increases after the start of the growth cycle and supports expansion of the growth zone. Growth reorientation involves a shift in the position and angle of the growth zone. In summary, these results support a new model of pollen tube growth.Key words: growth zone, oscillation, exocytosis, growth reorientation, differential interference contrast microscopy, refraction-free     

Imaging phosphatidylinositol 4-phosphate dynamics in living plant cells

Polyphosphoinositides represent a minor group of phospholipids, accounting for less than 1% of the total. Despite their low abundance, these molecules have been implicated in various signalling and membrane trafficking events. Phosphatidylinositol 4-phosphate (PtdIns4 P ) is the most abundant polyphosphoinositide. ³²Pi-labelling studies have shown that the turnover of PtdIns4 P is rapid, but little is known about where in the cell or plant this occurs. Here, we describe the use of a lipid biosensor that monitors PtdIns4 P dynamics in living plant cells. The biosensor consists of a fusion between a fluorescent protein and a lipid-binding domain that specifically binds PtdIns4 P , i.e. the pleckstrin homology domain of the human protein phosphatidylinositol-4-phosphate adaptor protein-1 (FAPP1). YFP–PH_FAPP1 was expressed in four plant systems: transiently in cowpea protoplasts, and stably in tobacco BY-2 cells, Medicago truncatula roots and Arabidopsis thaliana seedlings. All systems allowed YFP–PH_FAPP1 expression without detrimental effects. Two distinct fluorescence patterns were observed: labelling of motile punctate structures and the plasma membrane. Co-expression studies with organelle markers revealed strong co-labelling with the Golgi marker STtmd–CFP, but not with the endocytic/pre-vacuolar marker GFP–AtRABF2b. Co-expression with the Ptdins3 P biosensor YFP–2 × FYVE revealed totally different localization patterns. During cell division, YFP–PH_FAPP1 showed strong labelling of the cell plate, but PtdIns3 P was completely absent from the newly formed cell membrane. In root hairs of M. truncatula and A. thaliana , a clear PtdIns4 P gradient was apparent in the plasma membrane, with the highest concentration in the tip. This only occurred in growing root hairs, indicating a role for PtdIns4 P in tip growth.     

Constructing Level-2 Phylogenetic Networks from Triplets

Jansson and Sung showed that, given a dense set of input triplets T (representing hypotheses about the local evolutionary relationships of triplets of taxa), it is possible to determine in polynomial time whether there exists a level-1 network consistent with T, and if so, to construct such a network [24]. Here, we extend this work by showing that this problem is even polynomial time solvable for the construction of level-2 networks. This shows that, assuming density, it is tractable to construct plausible evolutionary histories from input triplets even when such histories are heavily nontree-like. This further strengthens the case for the use of triplet-based methods in the construction of phylogenetic networks. We also implemented the algorithm and applied it to yeast data.     

Promiscuous mitochondria in Cryptococcus gattii

Cryptococcus gattii is a primary pathogenic basidiomycetous yeast comprising four genotypic groups. Here we present data on two mitochondrial loci (MtLrRNA and ATP6 ). Two of the genotypic groups, namely amplified fragment length polymorphism (AFLP)5/VGIII and AFLP6/VGII, formed monophyletic lineages. The AFLP4/VGI genotypic group, however, possessed five different mitochondrial genotypes that did not form a monophyletic lineage. The majority of these isolates contained mitochondrial genomes that are partially identical to those found in isolates belonging to AFLP6/VGII, which is causing the ongoing and expanding Vancouver Island outbreak. Two out of four AFLP7/VGIV isolates contained an AFLP4/VGI allele of MtLrRNA. These observations are best explained by assuming a process of mitochondrial recombination. If this is true, mitochondrial recombination seems possible between cells belonging to different genotypic groups of C. gattii , especially between AFLP6/VGII or AFLP7/VGIV and AFLP4/VGI. We also have to assume that mitochondria, most likely, were transferred from cells belonging to AFLP6/VGII to AFLP4/VGI. As such a process of mitochondrial recombination is only possible after cell–cell conjugation, this may also allow the further exchange of genetic material, for example nuclear or plasmid in nature, between different genotypes of C. gattii . This may be relevant as it may provide a possible mechanism contributing to the modulation of virulence attributes of isolates, such as has been observed in the ongoing Vancouver Island outbreak of C. gattii .     

The dynamics of naturally acquired immune responses to Plasmodium falciparum sexual stage antigens Pfs230 & Pfs48/45 in a low endemic area in Tanzania

Background

Naturally acquired immune responses against sexual stages of P. falciparum can reduce the transmission of malaria from humans to mosquitoes. These antigens are candidate transmission-blocking vaccines but little is known about the acquisition of sexual stage immunity after exposure to gametocytes, or their longevity and functionality. We conducted a longitudinal study on functional sexual stage immune responses.

Methodology/Principal Findings

Parasitaemic individuals (n = 116) were recruited at a health centre in Lower Moshi, Tanzania. Patients presented with gametocytes (n = 16), developed circulating gametocytes by day 7 (n = 69) or between day 7 and 14 (n = 10) after treatment or did not develop gametocytes (n = 21). Serum samples were collected on the first day of gametocytaemia and 28 and 84 days post-enrolment (or d7, 28, 84 after enrolment from gametocyte-negative individuals). Antibody responses to sexual stage antigens Pfs230 and Pfs48/45 were detected in 20.7% (72/348) and 15.2% (53/348) of the samples, respectively, and were less prevalent than antibodies against asexual stage antigens MSP-1₁₉ (48.1%; 137/285) and AMA-1 (52.4%; 129/246)(p<0.001). The prevalence of anti-Pfs230 (p = 0.026) and anti-Pfs48/45 antibodies (p = 0.017) increased with longer duration of gametocyte exposure and had an estimated half-life of approximately 3 months. Membrane feeding experiments demonstrated a strong association between the prevalence and concentration of Pfs230 and Pfs48/45 antibodies and transmission reducing activity (TRA, p<0.01).

Conclusions/Significance

In a longitudinal study, anti-Pfs230 and Pf48/45 antibodies developed rapidly after exposure to gametocytes and were strongly associated with transmission-reducing activity. Our data indicate that the extent of antigen exposure is important in eliciting functional transmission-reducing immune responses.     

Jaw and long bone marrow derived osteoclasts differ in shape and their response to bone and dentin

Increasing evidence suggests the existence of osteoclast diversity. Here we investigated whether precursors obtained from marrow of the mandibula or long bone could give rise to phenotypically different osteoclasts. Formation of multinucleated cells was assessed after culturing mouse marrow cells of the two bone types with macrophage colony stimulating factor (M-CSF) and receptor activator of NFκB ligand (RANKL) for up to 10 days on plastic, bone or dentin. Two times more osteoclasts formed from long bone marrow cells on bone compared to dentin, whereas higher numbers of jaw osteoclasts formed on dentin. Resorption of dentin or bone was similar for osteoclasts formed from both types of precursors. In contrast to jaw marrow derived osteoclasts, long bone osteoclasts predominantly had a multi-compartmented shape, with at least two nuclei containing compartments per cell. Osteoclasts on bone contained two times more actin rings than osteoclasts on dentin, regardless of their precursor origin. However, the area per osteoclast covered by actin rings was similar (20%) for both substrates. This study suggests that marrow cells obtained from different bones give rise to different osteoclasts. The substrate on which the osteoclasts are generated plays a role in steering their formation rather than their resorption.     

Genome sequences of Alicycliphilus denitrificans strains BC and K601T

Alicycliphilus denitrificans strain BC and A. denitrificans strain K601(T) degrade cyclic hydrocarbons. These strains have been isolated from a mixture of wastewater treatment plant material and benzene-polluted soil and from a wastewater treatment plant, respectively, suggesting their role in bioremediation of soil and water. Although the strains are phylogenetically closely related, there are some clear physiological differences. The hydrocarbon cyclohexanol, for example, can be degraded by strain K601(T) but not by strain BC. Furthermore, both strains can use nitrate and oxygen as an electron acceptor, but only strain BC can use chlorate as electron acceptor. To better understand the nitrate and chlorate reduction mechanisms coupled to the oxidation of cyclic compounds, the genomes of A. denitrificans strains BC and K601(T) were sequenced. Here, we report the complete genome sequences of A. denitrificans strains BC and K601(T).