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111.
During intra-erythrocytic maturation, malaria parasites catabolize up to 80% of cellular haemoglobin. Haem is liberated inside the parasite and converted to haemozoin, preventing haem iron from participating in cell-damaging reactions. Several experimental techniques exploit the relatively large paramagnetic susceptibility of malaria-infected cells as a means of sorting cells or investigating haemoglobin degradation, but the source of the dramatic increase in cellular magnetic susceptibility during parasite growth has not been unequivocally determined. Plasmodium falciparum cultures were enriched using high-gradient magnetic fractionation columns and the magnetic susceptibility of cell contents was directly measured. The forms of haem iron in the erythrocytes were quantified spectroscopically. In the 3D7 laboratory strain, the parasites converted approximately 60% of host cell haemoglobin to haemozoin and this product was the primary source of the increase in cell magnetic susceptibility. Haemozoin iron was found to have a magnetic susceptibility of (11.0 ± 0.9) × 10? 3 mL mol? 1. The calculated volumetric magnetic susceptibility (SI units) of the magnetically enriched cells was (1.88 ± 0.60) × 10? 6 relative to water while that of uninfected cells was not significantly different from water. Magnetic enrichment of parasitised cells can therefore be considered dependent primarily on the magnetic susceptibility of the parasitised cells. 相似文献
112.
Rebecca T. Kimball Edward L. Braun F. Keith Barker Rauri C.K. Bowie Michael J. Braun Jena L. Chojnowski Shannon J. Hackett Kin-Lan Han John Harshman Victoria Heimer-Torres Wallace Holznagel Christopher J. Huddleston Ben D. Marks Kathleen J. Miglia William S. Moore Sushma Reddy Frederick H. Sheldon Jordan V. Smith Christopher C. Witt Tamaki Yuri 《Molecular phylogenetics and evolution》2009,50(3):654-660
113.
Ahmed Moustafa Jeannette E. Loram Jeremiah D. Hackett Donald M. Anderson F. Gerald Plumley Debashish Bhattacharya 《PloS one》2009,4(6)
Background
Paralytic shellfish poisoning (PSP) is a potentially fatal syndrome associated with the consumption of shellfish that have accumulated saxitoxin (STX). STX is produced by microscopic marine dinoflagellate algae. Little is known about the origin and spread of saxitoxin genes in these under-studied eukaryotes. Fortuitously, some freshwater cyanobacteria also produce STX, providing an ideal model for studying its biosynthesis. Here we focus on saxitoxin-producing cyanobacteria and their non-toxic sisters to elucidate the origin of genes involved in the putative STX biosynthetic pathway.Methodology/Principal Findings
We generated a draft genome assembly of the saxitoxin-producing (STX+) cyanobacterium Anabaena circinalis ACBU02 and searched for 26 candidate saxitoxingenes (named sxtA to sxtZ) that were recently identified in the toxic strain Cylindrospermopsis raciborskii T3. We also generated a draft assembly of the non-toxic (STX−) sister Anabaena circinalis ACFR02 to aid the identification of saxitoxin-specific genes. Comparative phylogenomic analyses revealed that nine putative STX genes were horizontally transferred from non-cyanobacterial sources, whereas one key gene (sxtA) originated in STX+ cyanobacteria via two independent horizontal transfers followed by fusion. In total, of the 26 candidate saxitoxin-genes, 13 are of cyanobacterial provenance and are monophyletic among the STX+ taxa, four are shared amongst STX+ and STX-cyanobacteria, and the remaining nine genes are specific to STX+ cyanobacteria.Conclusions/Significance
Our results provide evidence that the assembly of STX genes in ACBU02 involved multiple HGT events from different sources followed presumably by coordination of the expression of foreign and native genes in the common ancestor of STX+ cyanobacteria. The ability to produce saxitoxin was subsequently lost multiple independent times resulting in a nested relationship of STX+ and STX− strains among Anabaena circinalis strains. 相似文献114.
Reyes-Prieto A Hackett JD Soares MB Bonaldo MF Bhattacharya D 《Current biology : CB》2006,16(23):2320-2325
A single cyanobacterial primary endosymbiosis that occurred approximately 1.5 billion years ago is believed to have given rise to the plastid in the common ancestor of the Plantae or Archaeplastida--the eukaryotic supergroup comprising red, green (including land plants), and glaucophyte algae. Critical to plastid establishment was the transfer of endosymbiont genes to the host nucleus (i.e., endosymbiotic gene transfer [EGT]). It has been postulated that plastid-derived EGT played a significant role in plant nuclear-genome evolution, with 18% (or 4,500) of all nuclear genes in Arabidopsis thaliana having a cyanobacterial origin with about one-half of these recruited for nonplastid functions. Here, we determine whether the level of cyanobacterial gene recruitment proposed for Arabidopsis is of the same magnitude in the algal sisters of plants by analyzing expressed-sequence tag (EST) data from the glaucophyte alga Cyanophora paradoxa. Bioinformatic analysis of 3,576 Cyanophora nuclear genes shows that 10.8% of these with significant database hits are of cyanobacterial origin and one-ninth of these have nonplastid functions. Our data indicate that unlike plants, early-diverging algal groups appear to retain a smaller number of endosymbiont genes in their nucleus, with only a minor proportion of these recruited for nonplastid functions. 相似文献
115.
Cheviron ZA Hackett SJ Brumfield RT 《Proceedings. Biological sciences / The Royal Society》2006,273(1594):1613-1618
Avian plumage traits are the targets of both natural and sexual selection. Consequently, genetic changes resulting in plumage variation among closely related taxa might represent important evolutionary events. The molecular basis of such differences, however, is unknown in most cases. Sequence variation in the melanocortin-1 receptor gene (MC1R) is associated with melanistic phenotypes in many vertebrate taxa, including several avian species. The blue-crowned manakin (Lepidothrix coronata), a widespread, sexually dichromatic passerine, exhibits striking geographic variation in male plumage colour across its range in southern Central America and western Amazonia. Northern males are black with brilliant blue crowns whereas southern males are green with lighter blue crowns. We sequenced 810 bp of the MC1R coding region in 23 individuals spanning the range of male plumage variation. The only variable sites we detected among L. coronata sequences were four synonymous substitutions, none of which were strictly associated with either plumage type. Similarly, comparative analyses showed that L. coronata sequences were monomorphic at the three amino acid sites hypothesized to be functionally important in other birds. These results demonstrate that genes other than MC1R underlie melanic plumage polymorphism in blue-crowned manakins. 相似文献
116.
117.
Christine A. Hackett John E. Bradshaw Glenn J. Bryan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2014,127(9):1885-1904
Key message
Dense linkage maps derived by analysing SNP dosage in autotetraploids provide detailed information about the location of, and genetic model at, quantitative trait loci.Abstract
Recent developments in sequencing and genotyping technologies enable researchers to generate high-density single nucleotide polymorphism (SNP) genotype data for mapping studies. For polyploid species, the SNP genotypes are informative about allele dosage, and Hackett et al. (PLoS ONE 8:e63939, 2013) presented theory about how dosage information can be used in linkage map construction and quantitative trait locus (QTL) mapping for an F1 population in an autotetraploid species. Here, QTL mapping using dosage information is explored for simulated phenotypic traits of moderate heritability and possibly non-additive effects. Different mapping strategies are compared, looking at additive and more complicated models, and model fitting as a single step or by iteratively re-weighted modelling. We recommend fitting an additive model without iterative re-weighting, and then exploring non-additive models for the genotype means estimated at the most likely position. We apply this strategy to re-analyse traits of high heritability from a potato population of 190 F1 individuals: flower colour, maturity, height and resistance to late blight (Phytophthora infestans (Mont.) de Bary) and potato cyst nematode (Globodera pallida), using a map of 3839 SNPs. The approximate confidence intervals for QTL locations have been improved by the detailed linkage map, and more information about the genetic model at each QTL has been revealed. For several of the reported QTLs, candidate SNPs can be identified, and used to propose candidate trait genes. We conclude that the high marker density is informative about the genetic model at loci of large effects, but that larger populations are needed to detect smaller QTLs. 相似文献118.
119.
Rani A Afzali B Kelly A Tewolde-Berhan L Hackett M Kanhere AS Pedroza-Pacheco I Bowen H Jurcevic S Jenner RG Cousins DJ Ragheb JA Lavender P John S 《Journal of immunology (Baltimore, Md. : 1950)》2011,187(7):3721-3729
Blockade of IL-2R with humanized anti-CD25 Abs, such as daclizumab, inhibits Th2 responses in human T cells. Recent murine studies have shown that IL-2 also plays a significant role in regulating Th2 cell differentiation by activated STAT5. To explore the role of activated STAT5 in the Th2 differentiation of primary human T cells, we studied the mechanisms underlying IL-2 regulation of C-MAF expression. Chromatin immunoprecipitation studies revealed that IL-2 induced STAT5 binding to specific sites in the C-MAF promoter. These sites corresponded to regions enriched for markers of chromatin architectural features in both resting CD4 and differentiated Th2 cells. Unlike IL-6, IL-2 induced C-MAF expression in CD4 T cells with or without prior TCR stimulation. TCR-induced C-MAF expression was significantly inhibited by treatment with daclizumab or a JAK3 inhibitor, R333. Furthermore, IL-2 and IL-6 synergistically induced C-MAF expression in TCR-activated T cells, suggesting functional cooperation between these cytokines. Finally, both TCR-induced early IL4 mRNA expression and IL-4 cytokine expression in differentiated Th2 cells were significantly inhibited by IL-2R blockade. Thus, our findings demonstrate the importance of IL-2 in Th2 differentiation in human T cells and support the notion that IL-2R-directed therapies may have utility in the treatment of allergic disorders. 相似文献
120.