Merozoite surface protein 2 of Plasmodium falciparum: expression, structure, dynamics, and fibril formation of the conserved N-terminal domain

Merozoite surface protein 2 (MSP2) is a GPI-anchored protein on the surface of the merozoite stage of the malaria parasite Plasmodium falciparum. It is largely disordered in solution, but has a propensity to form amyloid-like fibrils under physiological conditions. The N-terminal conserved region (MSP2(1-25)) is part of the protease-resistant core of these fibrils. To investigate the structure and dynamics of this region, its ability to form fibrils, and the role of individual residues in these properties, we have developed a bacterial expression system that yields > or =10 mg of unlabeled or (15)N-labeled peptide per litre of culture. Two recombinant versions of MSP2(1-25), wild-type and a Y7A/Y16A mutant, have been produced. Detailed conformational analysis of the wild-type peptide and backbone (15)N relaxation data indicated that it contains beta-turn and nascent helical structures in the central and C-terminal regions. Residues 6-21 represent the most ordered region of the structure, although there is some flexibility around residues 8 and 9. The 10-residue sequence (MSP2(7-16)) (with two Tyr residues) was predicted to have a higher propensity for beta-aggregation than the 8-mer sequence (MSP2(8-15)), but there was no significant difference in conformation between MSP2(1-25) and [Y7A,Y16A]MSP2(1-25) and the rate of fibril formation was only slightly slower in the mutant. The peptide expression system described here will facilitate further mutational analyses to define the roles of individual residues in transient structural elements and fibril formation, and thus contribute to the further development of MSP2 as a malaria vaccine candidate.     

Forest Fragmentation Reduces Seed Dispersal of Duckeodendron cestroides, a Central Amazon Endemic

Fragmentation that alters mutualistic relationships between plants and frugivorous animals may reduce the seed dispersal of trees. We examined the effects of forest fragmentation on the distributions of seeds and seedlings of a Central Amazon endemic tree, Duckeodendron cestroides . In the dry seasons of 2002–2004, seeds and first-year seedlings were counted within wedge-shaped transects centered around Duckeodendron adults in fragments and nearby continuous forests at the Biological Dynamics of Forest Fragmentation Project. Analyses showed that fragmentation reduced seed dispersal quantity and quality. The percent and distance of dispersed seeds were both twice as great in continuous forest as in fragments. The distances of each tree's five furthest dispersed seeds were three times greater in continuous forest than fragments. Over the 3-yr study, 20 times more seeds were dispersed more than 10 m from parent crowns in continuous forest than fragments. A regression analysis showed more dispersed seeds at all distances in continuous forest than fragments. Dispersal differences were strong in 2002 and 2004, years of large fruit crops, but weak or absent in 2003, when fruit production was low. As distance from parent crowns increased, the number of seedlings declined more rapidly in fragments than continuous forest. Distance-dependent mortality between the seed and seedling stages appeared to be more important in continuous forest than fragments. This research provides ample, indirect evidence demonstrating that forest fragmentation can result in the breakdown of a seed dispersal mutualism, potentially jeopardizing the reproduction of a rare, tropical tree.     

New and general synthesis of beta-C-glycosylformaldehydes from easily available beta-C-glycosylpropanones

A highly effective method for the introduction of a formyl group at the anomeric position of pyranosides was developed via enolisation of beta-C-D-glycopyranosylpropan-2-one using thermodynamic conditions then oxidative cleavage of the more substituted double bond. This sequence affords the desired aldehydes that are conveniently protected as aminals for purification and storage and easily regenerated using Dowex resin H+. In this paper, the syntheses of nine differently protected aldehydes derived from d-glucose, d-galactose, lactose and N-acetyl-d-glucosamine are presented. Our strategy proved to be very efficient in most cases excepted in the D-mannose series.     

Sampling bias created by ampicillin in isolation media for Aeromonas

Members of the bacterial genus Aeromonas are widely isolated from aquatic environments and studied in part for their ability to act as opportunistic pathogens in a variety of animals. All aeromonads, with the exception of Aeromonas trota, are generally thought to be resistant to ampicillin, so the antibiotic is frequently added to isolation medium as a selective agent. In this study, 282 aeromonads from environmental sources were isolated on a medium without ampicillin and their resistance to ampicillin determined. Of the 104 of these isolates that were judged to be independent (nonredundant), 18 (17.3%) were susceptible to ampicillin. A chi-square analysis was performed to determine the impact of ampicillin use on enumerating Aeromonas species from environmental samples. Our results indicate that, when ampicillin is used as a selective agent, a significant portion of the aeromonad population in at least some environments can be omitted from isolation.     

Novel soil lineages of Archaea are present in semi-arid soils of eastern Australia

The diversity of Archaea was studied in vertisolic and loam soils of a semi-arid region in Australia. Sampling was undertaken at an agricultural site, two grassland environments, and a brigalow (Acacia harpophylla) woodland. Archaeal community structure was profiled using amplified ribosomal DNA restriction analysis (ARDRA) combined with rDNA sequencing of an example of each restriction fragment length polymorphism type. Sequence comparison and phylogenetic analysis demonstrated that both crenarchaeotal and euryarchaeotal Archaea were present at oxic depths in the soil at all field sites. Along with previously described soil archaeal lineages, novel soil lineages and the deeply divergent Pendant-33 group of Euryarchaeota were also detected. A novel statistical method for comparing ARDRA derived data was demonstrated and implemented using the archaeal communities from the four field sites. Archaeal diversity, as measured by this method, was significantly higher in the agricultural site than at either of the grassland sites or the brigalow woodland.     

Convergence and extension movements mediate the specification and fate maintenance of zebrafish slow muscle precursors

During vertebrate gastrulation, concurrent inductive events and cell movements fashion the body plan. Convergence and extension (C&E) gastrulation movements narrow the vertebrate embryonic body mediolaterally while elongating it rostrocaudally. Segmented somites are shaped and positioned by C&E alongside the notochord and differentiate into skeleton, fast, and slow muscles during somitogenesis. In zebrafish, simultaneous inactivation of non-canonical Wnt signaling components Knypek and Trilobite strongly impairs C&E gastrulation movements. Here we show that knypek;trilobite double mutants exhibit a severe deficit in slow muscles and their precursor, adaxial cells, revealing essential roles of C&E movements in adaxial cell development. Adaxial cells become distinguishable in the presomitic mesoderm during late gastrulation by their expression of myogenic factors and axial-adjacent position. Using cell tracing analyses and genetic manipulations, we demonstrate that C&E movements regulate the number of prospective adaxial cells specified during gastrulation by determining the size of the interface between the inductive axial and target presomitic tissues. During segmentation, when the range of Hedgehog signaling from the axial tissue declines, tight apposition of prospective adaxial cells to the notochord, which is achieved by convergence movements, is necessary for their continuous Hedgehog reception and fate maintenance. We provide direct evidence to show that the deficiency of adaxial cells in knypek;trilobite double mutants is due to impaired C&E movements, rather than an alteration in Hedgehog signal and its reception, or a cell-autonomous requirement for Knypek and Trilobite in adaxial cell development. Our results underscore the significance of precise coordination between cell movements and inductive tissue interactions during cell fate specification.     

The appendage role of insect disco genes and possible implications on the evolution of the maggot larval form

Though initially identified as necessary for neural migration, Disconnected and its partially redundant paralog, Disco-related, are required for proper head segment identity during Drosophila embryogenesis. Here, we present evidence that these genes are also required for proper ventral appendage development during development of the adult fly, where they specify medial to distal appendage development. Cells lacking the disco genes cannot contribute to the medial and distal portions of ventral appendages. Further, ectopic disco transforms dorsal appendages toward ventral fates; in wing discs, the medial and distal leg development pathways are activated. Interestingly, this appendage role is conserved in the red flour beetle, Tribolium (where legs develop during embryogenesis), yet in the beetle we found no evidence for a head segmentation role. The lack of an embryonic head specification role in Tribolium could be interpreted as a loss of the head segmentation function in Tribolium or gain of this function during evolution of flies. However, we suggest an alternative explanation. We propose that the disco genes always function as appendage factors, but their appendage nature is masked during Drosophila embryogenesis due to the reduction of limb fields in the maggot style Drosophila larva.     

The significance of multiple mating in the social wasp Vespula maculifrons

The evolution of the complex societies displayed by social insects depended partly on high relatedness among interacting group members. Therefore, behaviors that depress group relatedness, such as multiple mating by reproductive females (polyandry), are unexpected in social insects. Nevertheless, the queens of several social insect species mate multiply, suggesting that polyandry provides some benefits that counteract the costs. However, few studies have obtained evidence for links between rates of polyandry and fitness in naturally occurring social insect populations. We investigated if polyandry was beneficial in the social wasp Vespula maculifrons. We used genetic markers to estimate queen mate number in V. maculifrons colonies and assessed colony fitness by counting the number of cells that colonies produced. Our results indicated that queen mate number was directly, strongly, and significantly correlated with the number of queen cells produced by colonies. Because V. maculifrons queens are necessarily reared in queen cells, our results demonstrate that high levels of polyandry are associated with colonies capable of producing many new queens. These data are consistent with the explanation that polyandry is adaptive in V. maculifrons because it provides a fitness advantage to queens. Our research may provide a rare example of an association between polyandry and fitness in a natural social insect population and help explain why queens in this taxon mate multiply.     

The mixed mating system of Impatiens capensis and infection by a foliar rust pathogen: patterns of resistance and fitness consequences

Outcrossing by hosts may offer protection from natural enemies adapted to parental genotypes by creating diverse progeny that differ from their parents through genetic recombination. However, past experimental work addressing the relationship between mating system and disease in offspring has given conflicting results, suggesting that outcrossing might also cause the dissolution of resistant genotypes. To determine if selfed progeny are more susceptible to disease caused by the heteroecious rust, Puccinia recondita, or if selfing preserves existing resistant genotypes, we used a factorial design to compare levels of infection of selfed and outcrossed progeny of Impatiens capensis, a woodland annual with a mixed mating system. We compared the level of host infection when exposed to three pathogen sources in the field: the sympatric rust population, and two allopatric rust populations. Outcrossed progeny exposed to sympatric rust had higher infection scores than selfed progeny exposed to the same rust, suggesting that outcrossing breaks up resistant genotypes. In addition, there was a trend for the rust to be more infective on sympatric rather than allopatric hosts. We also examined whether rust infection differentially alters the fitness of selfed and outcrossed progeny. Outcrossed plants that escaped infection had higher fitness, as measured by fruit production, than selfed plants, but there was no difference in fitness between infected selfed and infected outcrossed plants. Thus, outcrossing was advantageous in the absence of disease, but there was no fitness difference between selfed and outcrossed progeny in the presence of disease. In sum, our results indicate that interactions with pathogens can eliminate or reverse the advantage of outcrossing.