Adaptation of the bovine spongiform encephalopathy agent to primates and comparison with Creutzfeldt-- Jakob disease: implications for human health.
(65/2155)
There is substantial scientific evidence to support the notion that bovine spongiform encephalopathy (BSE) has contaminated human beings, causing variant Creutzfeldt-Jakob disease (vCJD). This disease has raised concerns about the possibility of an iatrogenic secondary transmission to humans, because the biological properties of the primate-adapted BSE agent are unknown. We show that (i) BSE can be transmitted from primate to primate by intravenous route in 25 months, and (ii) an iatrogenic transmission of vCJD to humans could be readily recognized pathologically, whether it occurs by the central or peripheral route. Strain typing in mice demonstrates that the BSE agent adapts to macaques in the same way as it does to humans and confirms that the BSE agent is responsible for vCJD not only in the United Kingdom but also in France. The agent responsible for French iatrogenic growth hormone-linked CJD taken as a control is very different from vCJD but is similar to that found in one case of sporadic CJD and one sheep scrapie isolate. These data will be key in identifying the origin of human cases of prion disease, including accidental vCJD transmission, and could provide bases for vCJD risk assessment. (+info)
Complete genome sequence of Caulobacter crescentus.
(66/2155)
The complete genome sequence of Caulobacter crescentus was determined to be 4,016,942 base pairs in a single circular chromosome encoding 3,767 genes. This organism, which grows in a dilute aquatic environment, coordinates the cell division cycle and multiple cell differentiation events. With the annotated genome sequence, a full description of the genetic network that controls bacterial differentiation, cell growth, and cell cycle progression is within reach. Two-component signal transduction proteins are known to play a significant role in cell cycle progression. Genome analysis revealed that the C. crescentus genome encodes a significantly higher number of these signaling proteins (105) than any bacterial genome sequenced thus far. Another regulatory mechanism involved in cell cycle progression is DNA methylation. The occurrence of the recognition sequence for an essential DNA methylating enzyme that is required for cell cycle regulation is severely limited and shows a bias to intergenic regions. The genome contains multiple clusters of genes encoding proteins essential for survival in a nutrient poor habitat. Included are those involved in chemotaxis, outer membrane channel function, degradation of aromatic ring compounds, and the breakdown of plant-derived carbon sources, in addition to many extracytoplasmic function sigma factors, providing the organism with the ability to respond to a wide range of environmental fluctuations. C. crescentus is, to our knowledge, the first free-living alpha-class proteobacterium to be sequenced and will serve as a foundation for exploring the biology of this group of bacteria, which includes the obligate endosymbiont and human pathogen Rickettsia prowazekii, the plant pathogen Agrobacterium tumefaciens, and the bovine and human pathogen Brucella abortus. (+info)
Differential CD4/CCR5 utilization, gp120 conformation, and neutralization sensitivity between envelopes from a microglia-adapted human immunodeficiency virus type 1 and its parental isolate.
(67/2155)
Human immunodeficiency virus type 1 (HIV-1) infects and induces syncytium formation in microglial cells from the central nervous system (CNS). A primary isolate (HIV-1(BORI)) was sequentially passaged in cultured microglia, and the isolate recovered (HIV-1(BORI-15)) showed high levels of fusion and replicated more efficiently in microglia (J. M. Strizki, A. V. Albright, H. Sheng, M. O'Connor, L. Perrin, and F. Gonzalez-Scarano, J. Virol. 70:7654-7662, 1996). The parent and adapted viruses used CCR5 as coreceptor. Recombinant viruses demonstrated that the syncytium-inducing phenotype was associated with four amino acid differences in the V1/V2 region of the viral gp120 (J. T. C. Shieh, J. Martin, G. Baltuch, M. H. Malim, and F. Gonzalez-Scarano, J. Virol. 74:693-701, 2000). We produced luciferase-reporter, env-pseudotyped viruses using plasmids containing env sequences from HIV-1(BORI), HIV-1(BORI-15), and the V1/V2 region of HIV-1(BORI-15) in the context of HIV-1(BORI) env (named rBORI, rB15, and rV1V2, respectively). The pseudotypes were used to infect cells expressing various amounts of CD4 and CCR5 on the surface. In contrast to the parent recombinant, the rB15 and rV1V2 pseudotypes retained their infectability in cells expressing low levels of CD4 independent of the levels of CCR5, and they infected cells expressing CD4 with a chimeric coreceptor containing the third extracellular loop of CCR2b in the context of CCR5 or a CCR5 Delta4 amino-terminal deletion mutant. The VH-rB15 and VH-rV1V2 recombinant viruses were more sensitive to neutralization by a panel of HIV-positive sera than was VH-rBORI. Interestingly, the CD4-induced 17b epitope on gp120 was more accessible in the rB15 and rV1V2 pseudotypes than in rBORI, even before CD4 binding, and concomitantly, the rB15 and rV1V2 pseudotypes were more sensitive to neutralization with the human 17b monoclonal antibody. Adaptation to growth in microglia--cells that have reduced expression of CD4 in comparison with other cell types--appears to be associated with changes in gp120 that modify its ability to utilize CD4 and CCR5. Changes in the availability of the 17b epitope indicate that these affect conformation. These results imply that the process of adaptation to certain tissue types such as the CNS directly affects the interaction of HIV-1 envelope glycoproteins with cell surface components and with humoral immune responses. (+info)
Computational genomics.
(68/2155)
We now know how to read the sequences of nucleotide letters that comprise the genome at a rather frightening speed--a several-million-base bacterial genome in several days is not a problem for one of the sequencing centers, and a billion-base eukaryotic genome can be done in less than a year. But reading a text and understanding it are two different things. So how well can we understand the genome sequences? The answer to this question is central to the whole enterprise of genomics, and this is where computational analysis of genomes takes the driver's seat. Here I will try to briefly outline some major goals, problems, challenges and approaches of computational genomics. Such a young field is already quite diverse, and in this short article I will concentrate on several issues that seen to be critical for deciphering biology from genome sequences, rather than mathematical and computer-science aspects that are well covered in several excellent books. (+info)
Selective mRNA degradation by polynucleotide phosphorylase in cold shock adaptation in Escherichia coli.
(69/2155)
Upon cold shock, Escherichia coli cell growth transiently stops. During this acclimation phase, specific cold shock proteins (CSPs) are highly induced. At the end of the acclimation phase, their synthesis is reduced to new basal levels, while the non-cold shock protein synthesis is resumed, resulting in cell growth reinitiation. Here, we report that polynucleotide phosphorylase (PNPase) is required to repress CSP production at the end of the acclimation phase. A pnp mutant, upon cold shock, maintained a high level of CSPs even after 24 h. PNPase was found to be essential for selective degradation of CSP mRNAs at 15 degrees C. In a poly(A) polymerase mutant and a CsdA RNA helicase mutant, CSP expression upon cold shock was significantly prolonged, indicating that PNPase in concert with poly(A) polymerase and CsdA RNA helicase plays a critical role in cold shock adaptation. (+info)
Rapid changes in polyphosphate content within acidocalcisomes in response to cell growth, differentiation, and environmental stress in Trypanosoma cruzi.
(70/2155)
Inorganic polyphosphate (polyP) has been identified and measured in different stages of Trypanosoma cruzi. Millimolar levels (in terms of P(i) residues) in chains of less than 50 residues long, and micromolar levels in chains of about 700--800 residues long, were found in different stages of T. cruzi. Analysis of purified T. cruzi acidocalcisomes indicated that polyPs were preferentially located in these organelles. This was confirmed by visualization of polyPs in the acidocalcisomes using 4',6-diamidino-2-phenylindole. A rapid increase (within 2--4 h) in the levels of short and long chain polyPs was detected during trypomastigote to amastigote differentiation and during the lag phase of growth of epimastigotes (within 12--24 h). Levels rapidly decreased after the epimastigotes resumed growth. Short and long chain polyP levels rapidly decreased upon exposure of epimastigotes to hypo-osmotic or alkaline stresses, whereas levels increased after hyperosmotic stress. Ca(2+) release from acidocalcisomes by a combination of ionophores (ionomycin and nigericin) was associated with the hydrolysis of short and long chain polyPs. In agreement with these results, acidocalcisomes were shown to contain polyphosphate kinase and exopolyphosphatase activities. Together, these results suggest a critical role for these organelles in the adaptation of the parasite to environmental changes. (+info)
Males' evolutionary responses to experimental removal of sexual selection.
(71/2155)
We evaluated the influence of pre- and post-copulatory sexual selection upon male reproductive traits in a naturally promiscuous species, Drosophila melanogaster. Sexual selection was removed in two replicate populations through enforced monogamous mating with random mate assignment or retained in polyandrous controls. Monogamous mating eliminates all opportunities for mate competition, mate discrimination, sperm competition, cryptic female choice and, hence, sexual conflict. Levels of divergence between lines in sperm production and male fitness traits were quantified after 38-81 generations of selection. Three a priori predictions were tested: (i) male investment in spermatogenesis will be lower in monogamy-line males due to the absence of sperm competition selection, (ii) due to the evolution of increased male benevolence, the fitness of females paired with monogamy-line males will be higher than that of females paired with control-line males, and (iii) monogamy-line males will exhibit decreased competitive reproductive success relative to control-line males. The first two predictions were supported, whereas the third prediction was not. Monogamy males evolved a smaller body size and the size of their testes and the number of sperm within the testes were disproportionately further reduced. In contrast, the fitness of monogamous males (and their mates) was greater when reproducing in a non-competitive context: females mated once with monogamous males produced offspring at a faster rate and produced a greater total number of surviving progeny than did females mated to control males. The results indicate that sexual selection favours the production of increased numbers of sperm in D. melanogaster and that sexual selection favours some male traits conferring a direct cost to the fecundity of females. (+info)
Calorimetrically obtained information about the efficiency of ectoine synthesis from glucose in Halomonas elongata.
(72/2155)
Compatible solutes are becoming more and more attractive commercially. Thus, knowledge of the efficiency of synthesis of compatible solutes from different carbon substrates is very important. As the growth rate and rates of formation of compatible solutes correspond to the heat flux, calorimetric measurements are particularly suitable for providing this information. By growing microorganisms continuously in a calorimeter, and generating a feeding stream with gradually increasing salinity without changing any other growth conditions, we were able to determine the efficiency of growth-associated synthesis of compatible solutes. This was shown for Halomonas elongata DMSZ 2581(T) growing on glucose, which synthesizes (at 25 degrees C) 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) as its main osmotic counterweight. The requirement of biologically usable energy for its growth-associated synthesis was found to be very low: a 100% efficiency of the conversion of the substrate-carbon into ectoine is both theoretically possible and was reached approximately in practice. The growth rate and yield coefficient were essentially independent of the ectoine formation rate, and the rate of substrate-carbon assimilation was far greater than the rate of dissimilation. The specific maximum growth rate was limited by the rate of formation of ectoine. (+info)