Recent evolutionary history of American Onchocerca volvulus, based on analysis of a tandemly repeated DNA sequence family

Polymerase chain reaction (PCR) products were characterized for a repeated sequence family (designated "O-150") of the human filarial parasite Onchocerca volvulus. In phylogenetic inferences, the O-150 sequences clustered into closely related groups, suggesting that concerted evolution maintains sequence homology in this family. Using a novel mathematical model based on a nested application of an analysis of variance, we demonstrated that African rainforest and savannah strain parasite populations are significantly different. In contrast, parasites collected in the New World are indistinguishable from African savannah strains of O. volvulus. This finding supports the hypothesis that onchocerciasis was recently introduced into the New World, possibly as a result of the slave trade.      

Architecture of Branch-root Junctions in Maize: Structure of the Connecting Xylem and the Porosity of Pit Membranes

The architecture of the connecting xylem network in the vascularplexus linking branch and main root vessels has been examinedusing cryoSEM, and the limiting porosity of the network determinedwith tracers (dye, and particles of known size: latex, polystyreneand gold sols). Dye and water move freely throughout the xylemnetwork, while particles are constrained to follow tortuousvessel-like conduits of irregularly-shaped elements linked bylarge-diameter perforations. These conduits end at special pitmembranes (boundary pit membranes) at the periphery of mainroot vessels. Particles accumulate on the outer side of thesefilters, often filling the terminal elements of these conduitsadjacent to the main root vessels. Some vessel elements withinthe plexus are isolated from the convoluted conduits by normalpit membranes, and often also from each other, by pit membranesand still-intact end walls in otherwise mature elements. Theseextra-conduit elements may be an auxiliary filtering system.The boundary pit membranes filtered out particles with meandiameters as small as 4.9 ± 0.7 nm, indicating a poresize one or two orders of magnitude smaller than most previousmeasurements for pit membranes, but close to pore sizes determinedfor hydrated primary cell walls. It is concluded that boundarypit membranes at branch-root junctions are efficient filtersfor microbes and particulates entering damaged branch roots.They would also restrict entry of air/water interfaces whenmain root xylem tension was less than approx. 100 MPa. Copyright2000 Annals of Botany Company Zea mays, air-seeding, branch-root junction, cryoSEM, embolisms, maize, pit membrane, pore size, xylem, water transport     

Use of bioluminescent aequorin for the pharmacological characterization of 5HT receptors.

A convenient functional assay for 5HT2a and 5HT2c receptors is reported utilizing the bioluminescent aequorin to detect intracellular calcium changes. Using this assay, the pharmacological properties of many 5HT ligands can be determined in a 96-well format. The data indicate that the aequorin detection method is superior to the inositol phosphate assay with regard to speed and scope. This system is also appropriate for kinetic studies of receptor desensitization. We showed that the human 5HT2c receptor desensitizes in a biphasic manner, with a fast desensitization of approximately 90% of the total response occurring within 15 minutes while the remaining 10% response remains for at least 3 hours.     

Discovery of a small molecule that inhibits cell division by blocking FtsZ,a novel therapeutic target of antibiotics

The emergence of bacterial resistance to antibiotics is a major health problem and, therefore, it is critical to develop new antibiotics with novel modes of action. FtsZ, a tubulin-like GTPase, plays an essential role in bacterial cell division, and its homologs are present in almost all eubacteria and archaea. During cell division, FtsZ forms polymers in the presence of GTP that recruit other division proteins to make the cell division apparatus. Therefore, inhibition of FtsZ polymerization will prevent cells from dividing, leading to cell death. Using a fluorescent FtsZ polymerization assay, the screening of >100,000 extracts of microbial fermentation broths and plants followed by fractionation led to the identification of viriditoxin, which blocked FtsZ polymerization with an IC50 of 8.2 microg/ml and concomitant GTPase inhibition with an IC50 of 7.0 microg/ml. That the mode of antibacterial action of viriditoxin is via inhibition of FtsZ was confirmed by the observation of its effects on cell morphology, macromolecular synthesis, DNA-damage response, and increased minimum inhibitory concentration as a result of an increase in the expression of the FtsZ protein. Viriditoxin exhibited broad-spectrum antibacterial activity against clinically relevant Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci, without affecting the viability of eukaryotic cells.     

Self-assemblage formation in a social insect: the protective curtain of a honey bee swarm

Summary. This paper considers a little-studied topic in the biology of social insects: the formation of self-assemblages. It focuses on the mechanisms whereby the outermost workers in a bivouacked swarm of honey bees, when rained upon, form a water repellent curtain of bees over the swarm cluster. Specifically, we analyzed how the worker bees in the mantle of a swarm cluster adjust their body orientation, wing spread, and inter-individual spacing to form a protective curtain when wetted. When warm and dry, the mantle bees orient their bodies weakly with respect to gravity, do not tuck their heads under adjacent bees, have high variability in wing spread, and space themselves widely. In contrast, when warm and wet, the mantle bees orient uniformly with head upward, tuck their heads beneath the abdomens of bees above, hold their wings together, and press tightly together. This produces a surface that closely resembles a tiled roof. When cool and dry, the mantle bees generally orient their bodies with head upward, press their heads into the interior of the cluster, hold their wings wide apart, and draw close together. We also examined the age distribution of the mantle bees. Older bees are more likely than younger bees to be found in the mantle of a swarm, perhaps because younger bees are more important than older bees to colony survival after swarming and so occupy a more sheltered position in a swarm. Finally, we tested whether swarm clusters that have formed a protective curtain shed water more effectively than ones that have not formed a curtain. We found that this is the case.Received 28 November 2003; revised 29 February 2004; accepted 11 April 2004.     

Adult Song Sparrows do not Alter their Song Repertoires

To understand fully the function of vocal learning, it is important to know when, during an individual's lifetime, learning occurs. Songbirds are generally categorized into two groups with respect to their adult song learning ability. 'Open-ended' song learners are able to learn to produce new songs in adulthood, whereas 'age-limited' song learners can only acquire songs during their first year of life. Researchers have long assumed that certain oscine species are open-ended or age-limited song learners, but the evidence to date has been inadequate to test these assumptions for most species. We tested the hypothesis that song sparrows ( Melospiza melodia ) are age-limited song learners who do not alter their song repertoires in adulthood by examining the song repertoires of 24 color-banded males who were fully recorded in two, three or four different years. We compared sonagrams of the song types produced by males in different years and looked for any changes in repertoire composition (i.e. added or dropped song types). With few exceptions, males produced song repertoires that were identical in every year they were recorded. The exceptions (four males who did not produce one of their song types during one recording session) were all cases in which we believe that we missed recording a song type that a male did indeed have, not that the males dropped a song type. The finding that adult males do not alter the composition of their song repertoires provides strong evidence that song sparrows are age-limited song learners. Although it is possible that song sparrows make subtle within-song type changes across years, such changes would not necessarily constitute new song learning.     

Imidazopyridyl compounds as aldosterone synthase inhibitors

The inhibition of aldosterone synthase (CYP11B2) may be an effective treatment of hypertension and heart failure, among other ailments. Previously reported benzimidazole CYP11B2 inhibitors led the way for bioisosteric imidazopyridines that are both potent and selective over CYP11B1.     

Identification of valid reference genes for the normalization of RT qPCR gene expression data in human brain tissue

Background

Transfection of cells with gene-specific, single-stranded oligonucleotides can induce the targeted exchange of one or two nucleotides in the targeted gene. To characterize the features of the DNA-repair mechanisms involved, we examined the maximal distance for the simultaneous exchange of two nucleotides by a single-stranded oligonucleotide. The chosen experimental system was the correction of a hprt-point mutation in a hamster cell line, the generation of an additional nucleotide exchange at a variable distance from the first exchange position and the investigation of the rate of simultaneous nucleotide exchanges.

Results

The smaller the distance between the two exchange positions, the higher was the probability of a simultaneous exchange. The detected simultaneous nucleotide exchanges were found to cluster in a region of about fourteen nucleotides upstream and downstream from the first exchange position.

Conclusion

We suggest that the mechanism involved in the repair of the targeted DNA strand utilizes only a short sequence of the single-stranded oligonucleotide, which may be physically incorporated into the DNA or be used as a matrix for a repair process.     

Effects of a habitat-altering invader on nesting sparrows: An ecological trap?

Many invading species impact native species through predation, parasitism or competition, while others affect natives indirectly by restructuring their habitat. How invasive plants affect native animals, and to what extent native animals respond to changes in their habitat and the novel selection pressures that follow, is not well known. We investigated the impacts of a habitat-altering invader, the Atlantic cordgrass Spartina alterniflora, on the nesting success of Alameda song sparrows (Melospiza melodia pusillula), a California Species of Special Concern, in tidal marshes in three sites in San Francisco Bay. Date of laying was the most influential factor in determining daily survival rate of nests, but whether the nest was placed in exotic Spartina was the most important ecological variable. Nests placed in exotic Spartina had a success rate that was 30% lower than those placed in native vegetation. Nests in exotic Spartina were significantly more likely to fail due to tidal flooding than were nests placed in native vegetation, because the densest stands of exotic Spartina occurred at significantly lower elevations relative to the tides. Our results suggest that exotic Spartina may be an ecological trap for song sparrows in San Francisco Bay, attracting birds to nest sites that are often destroyed by tidal flooding.     

Evidence That the EphA2 Receptor Exacerbates Ischemic Brain Injury

Ephrin (Eph) signaling within the central nervous system is known to modulate axon guidance, synaptic plasticity, and to promote long-term potentiation. We investigated the potential involvement of EphA2 receptors in ischemic stroke-induced brain inflammation in a mouse model of focal stroke. Cerebral ischemia was induced in male C57Bl6/J wild-type (WT) and EphA2-deficient (EphA2^−/−) mice by middle cerebral artery occlusion (MCAO; 60 min), followed by reperfusion (24 or 72 h). Brain infarction was measured using triphenyltetrazolium chloride staining. Neurological deficit scores and brain infarct volumes were significantly less in EphA2^−/− mice compared with WT controls. This protection by EphA2 deletion was associated with a comparative decrease in brain edema, blood-brain barrier damage, MMP-9 expression and leukocyte infiltration, and higher expression levels of the tight junction protein, zona occludens-1. Moreover, EphA2^−/− brains had significantly lower levels of the pro-apoptotic proteins, cleaved caspase-3 and BAX, and higher levels of the anti-apoptotic protein, Bcl-2 as compared to WT group. We confirmed that isolated WT cortical neurons express the EphA2 receptor and its ligands (ephrin-A1–A3). Furthermore, expression of all four proteins was increased in WT primary cortical neurons following 24 h of glucose deprivation, and in the brains of WT mice following stroke. Glucose deprivation induced less cell death in primary neurons from EphA2^−/− compared with WT mice. In conclusion, our data provide the first evidence that the EphA2 receptor directly contributes to blood-brain barrier damage and neuronal death following ischemic stroke.