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91.
Atwill ER Phillips R Pereira MD Li X McCowan B 《Applied and environmental microbiology》2004,70(11):6748-6752
Twelve percent of 853 California ground squirrels (Spermophilus beecheyi) from six different geographic locations in Kern County, Calif., were found to be shedding on average 44,482 oocysts g of feces(-1). The mean annual environmental loading rate of Cryptosporidium oocysts was 57,882 oocysts squirrel(-1) day(-1), with seasonal patterns of fecal shedding ranging from <10,000 oocysts squirrel(-1) day(-1) in fall, winter, and spring to levels of 2 x 10(5) oocysts squirrel(-1) day(-1) in summer. Juveniles were about twice as likely as adult squirrels to be infected and shed higher concentrations of oocysts than adults did, with particularly high levels of infection and shedding being found among juvenile male squirrels. Based on DNA sequencing of a portion of the 18S small-subunit rRNA gene, there existed three genotypes of Cryptosporidium species in these populations of squirrels (Sbey03a, Sbey03b, and Sbey03c; accession numbers AY462231 to AY462233, respectively). These unique DNA sequences were most closely related (96 to 97% homology) to porcine C. parvum (AF115377) and C. wrairi (AF115378). Inoculating BALB/c neonatal mice with up to 10,000 Sbey03b or Sbey03c fresh oocysts from different infected hosts did not produce detectable levels of infection, suggesting that this common genotype shed by California ground squirrels is not infectious for mice and may constitute a new species of Cryptosporidium. 相似文献
92.
Xu Z Escamilla-Treviño L Zeng L Lalgondar M Bevan D Winkel B Mohamed A Cheng CL Shih MC Poulton J Esen A 《Plant molecular biology》2004,55(3):343-367
In plants, Glycoside Hydrolase (GH) Family 1 -glycosidases are believed to play important roles in many diverse processes including chemical defense against herbivory, lignification, hydrolysis of cell wall-derived oligosaccharides during germination, and control of active phytohormone levels. Completion of the Arabidopsis thalianagenome sequencing project has enabled us, for the first time, to determine the total number of Family 1 members in a higher plant. Reiterative database searches revealed a multigene family of 48 members that includes eight probable pseudogenes. Manual reannotation and analysis of the entire family were undertaken to rectify existing misannotations and identify phylogenetic relationships among family members. Forty-seven members (designated BGLU1 through BGLU47) share a common evolutionary origin and were subdivided into approximately 10 subfamilies based on phylogenetic analysis and consideration of intron–exon organizations. The forty-eighth member of this family (At3g06510; sfr2) is a -glucosidase-like gene that belongs to a distinct lineage. Information pertaining to expression patterns and potential functions of Arabidopsis GH Family 1 members is presented. To determine the biological function of all family members, we intend to investigate the substrate specificity of each mature hydrolase after its heterologous expression in the Pichia pastoris expression system. To test the validity of this approach, the BGLU44-encoded hydrolase was expressed in P. pastoris and purified to homogeneity. When tested against a wide range of natural and synthetic substrates, this enzyme showed a preference for -mannosides including 1,4--D-mannooligosaccharides, suggesting that it may be involved in A. thaliana in degradation of mannans, galactomannans, or glucogalactomannans. Supporting this notion, BGLU44 shared high sequence identity and similar gene organization with tomato endosperm -mannosidase and barley seed -glucosidase/-mannosidase BGQ60. 相似文献
93.
Radial arm maze performance of rats following repeated low level microwave radiation exposure 总被引:5,自引:0,他引:5
We examined the possibility of changes in "working" memory of rats following whole body exposure to microwave (MW) radiation. During each of 10 days, we exposed rats within circularly polarized waveguides for 45 min to 2450 MHz fields at whole body SARs of 0.6 W/kg (2 micros pulses, 500 pps), followed by testing in a 12 arm, radial arm maze (RAM). Rats received a preexposure injection of one of three psychoactive compounds or saline, to determine whether a compound would interact with MW exposure to affect performance in the maze. Error rate, i.e., reentry into arms already visited, and time to criterion data for 10 consecutive days of testing were analyzed by a three way analysis of variance (ANOVA) using main effects of "exposure" and "drug" and a repeated factor of "test day." Our alpha limit for significance was P <.05. Analyzes of error rates revealed no significant exposure effect, no significant drug effect and no significant interaction between the two main factors. There was a significant difference in test days, as expected, with repeated test-trial days, which indicates that learning was accomplished. There was no significant interaction of test day and the other two factors. The results of our analyzes of time to criterion data included no significant exposure effect, a significant drug effect, a significant test day effect, and a significant interaction between drug and test day factors. Post hoc analyzes of the drug factor revealed that rats treated with either physostigmine or nalrexone hydrochloride, took significantly longer to complete the maze task than rats pretreated with saline or with naloxone methodide. We conclude that there is no evidence from the current study that exposure to of MW radiation under parameters examined caused decrements in the ability of rats to learn the spatial memory task. 相似文献
94.
U8 snoRNP is required for accumulation of mature 5.8S and 28S rRNA in vertebrates. We are identifying proteins that bind U8 RNA with high specificity to understand how U8 functions in ribosome biogenesis. Here, we characterize a Xenopus 29 kDa protein (X29), which we previously showed binds U8 RNA with high affinity. X29 and putative homologs in other vertebrates contain a NUDIX domain found in MutT and other nucleotide diphosphatases. Recombinant X29 protein has diphosphatase activity that removes m(7)G and m(227)G caps from U8 and other RNAs in vitro; the putative 29 kDa human homolog also displays this decapping activity. X29 is primarily nucleolar in Xenopus tissue culture cells. We propose that X29 is a member of a conserved family of nuclear decapping proteins that function in regulating the level of U8 snoRNA and other nuclear RNAs with methylated caps. 相似文献
95.
Filla MB Czirók A Zamir EA Little CD Cheuvront TJ Rongish BJ 《Birth defects research. Part C, Embryo today : reviews》2004,72(3):267-276
Vertebrate axis patterning depends on cell and extracellular matrix (ECM) repositioning and proper cell-ECM interactions. However, there are few in vivo data addressing how large-scale tissue deformations are coordinated with the motion of local cell ensembles or the displacement of ECM constituents. Combining the methods of dynamic imaging and experimental biology allows both cell and ECM fate-mapping to be correlated with ongoing tissue deformations. These fate-mapping studies suggest that the axial ECM components "move" both as a composite meshwork and as autonomous particles, depending on the length scale being examined. Cells are also part of this composite, and subject to passive displacements resulting from tissue deformations. However, in contrast to the ECM, cells are self-propelled. The net result of cell and ECM displacements, along with proper ECM-cell adhesion, is the assembly of new tissue architecture. Data herein show that disruption of normal cell-ECM interactions during axis formation results in developmental abnormalities and a disorganization of the ECM. Our goal in characterizing the global displacement patterns of axial cells and ECM is to provide critical information regarding existing strain fields in the segmental plate and paraxial mesoderm. Deducing the mechanical influences on cell behavior is critical, if we are to understand vertebral axis patterning. Supplementary material for this article is available online at http://www.mrw.interscience.wiley.com/suppmat/1542-975X/suppmat/72/v72.266.html. 相似文献
96.
Assembly and characterization of heterochromatin and euchromatin on human artificial chromosomes
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Background
Human centromere regions are characterized by the presence of alpha-satellite DNA, replication late in S phase and a heterochromatic appearance. Recent models propose that the centromere is organized into conserved chromatin domains in which chromatin containing CenH3 (centromere-specific H3 variant) at the functional centromere (kinetochore) forms within regions of heterochromatin. To address these models, we assayed formation of heterochromatin and euchromatin on de novo human artificial chromosomes containing alpha-satellite DNA. We also examined the relationship between chromatin composition and replication timing of artificial chromosomes.Results
Heterochromatin factors (histone H3 lysine 9 methylation and HP1α) were enriched on artificial chromosomes estimated to be larger than 3 Mb in size but depleted on those smaller than 3 Mb. All artificial chromosomes assembled markers of euchromatin (histone H3 lysine 4 methylation), which may partly reflect marker-gene expression. Replication timing studies revealed that the replication timing of artificial chromosomes was heterogeneous. Heterochromatin-depleted artificial chromosomes replicated in early S phase whereas heterochromatin-enriched artificial chromosomes replicated in mid to late S phase.Conclusions
Centromere regions on human artificial chromosomes and host chromosomes have similar amounts of CenH3 but exhibit highly varying degrees of heterochromatin, suggesting that only a small amount of heterochromatin may be required for centromere function. The formation of euchromatin on all artificial chromosomes demonstrates that they can provide a chromosome context suitable for gene expression. The earlier replication of the heterochromatin-depleted artificial chromosomes suggests that replication late in S phase is not a requirement for centromere function.97.
98.
Govindasamy L Kukar T Lian W Pedersen B Gu Y Agbandje-McKenna M Jin S McKenna R Wu D 《Journal of structural biology》2004,146(3):416-424
We report the crystal structure of a binary complex of human peroxisomal carnitine acetyltransferase and the substrate l-carnitine, refined to a resolution of 1.8 Angstrom with an R(factor) value of 18.9% (R(free)=22.3%). L-carnitine binds to a preformed pocket in the active site tunnel of carnitine acetyltransferase aligned with His(322). The quaternary nitrogen of carnitine forms a pi-cation interaction with Phe(545), while Arg(497) forms an electrostatic interaction with the negatively charged carboxylate group. An extensive hydrogen bond network also occurs between the carboxylate group and Tyr(431), Thr(444), and a bound water molecule. Site-directed mutagenesis and kinetic characterization reveals that Tyr(431), Thr(444), Arg(497), and Phe(545) are essential for high affinity binding of L-carnitine. 相似文献
99.
Chronic hypoxia in development selectively alters the activities of key enzymes of glucose oxidative metabolism in brain regions 总被引:2,自引:0,他引:2
Lai JC White BK Buerstatte CR Haddad GG Novotny EJ Behar KL 《Neurochemical research》2003,28(6):933-940
The immature brain is more resistant to hypoxia/ischemia than the mature brain. Although chronic hypoxia can induce adaptive-changes on the developing brain, the mechanisms underlying such adaptive changes are poorly understood. To further elucidate some of the adaptive changes during postnatal hypoxia, we determined the activities of four enzymes of glucose oxidative metabolism in eight brain regions of hypoxic and normoxic rats. Litters of Sprague-Dawley rats were put into the hypoxic chamber (oxygen level maintained at 9.5%) with their dams starting on day 3 postnatal (P3). Age-matched normoxic rats were use as control animals. In P10 hypoxic rats, lactate dehydrogenase (LDH) activity in cerebral cortex, striatum, olfactory bulb, hippocampus, hypothalamus, pons and medulla, and cerebellum was significantly increased (by 100%–370%) compared to those in P10 normoxic rats. In P10 hypoxic rats, hexokinase (HK) activity in hypothalamus, hippocampus, olfactory bulb, midbrain, and cerebral cortex was significantly decreased (by 15%–30%). Neither -ketoglutarate dehydrogenase complex (KGDHC, which is believed to have an important role in the regulation of the tricarboxylic acid [TCA] cycle flux) nor citrate synthase (CS) activity was significantly decreased in the eight regions of P10 hypoxic rats compared to those in P10 normoxic rats. In P30 hypoxic rats, LDH activity was only increased in striatum (by 19%), whereas HK activity was only significantly decreased (by 30%) in this region. However, KGDHC activity was significantly decreased in olfactory bulb, hippocampus, hypothalamus, cerebral cortex, and cerebellum (by 20%–40%) in P30 hypoxic rats compared to those in P30 normoxic rats. Similarly, CS activity was decreased, but only in olfactory bulb, hypothalamus, and midbrain (by 9%–21%) in P30 hypoxic rats. Our results suggest that at least some of the mechanisms underlying the hypoxia-induced changes in activities of glycolytic enzymes implicate the upregulation of HIF-1. Moreover, our observation that chronic postnatal hypoxia induces differential effects on brain glycolytic and TCA cycle enzymes may have pathophysiological implications (e.g., decreased in energy metabolism) in childhood diseases (e.g., sudden infant death syndrome) in which hypoxia plays a role. 相似文献
100.
Dobson DE Scholtes LD Valdez KE Sullivan DR Mengeling BJ Cilmi S Turco SJ Beverley SM 《The Journal of biological chemistry》2003,278(18):15523-15531
Lipophosphoglycan (LPG) is an abundant surface molecule that plays key roles in the infectious cycle of Leishmania major. The dominant feature of LPG is a polymer of phosphoglycan (PG) (6Galbeta1,4Manalpha1-PO(4)) repeating units. In L. major these are extensively substituted with Gal(beta1,3) side chains, which are required for binding to midgut lectins and survival. We utilized evolutionary polymorphisms in LPG structure and cross-species transfections to recover genes encoding the LPG side chain beta1,3-galactosyltransferases (betaGalTs). A dispersed family of six SCG genes was recovered, whose predicted proteins exhibited characteristics of eukaryotic GalTs. At least four of these proteins showed significant LPG side chain betaGalT activity; SCG3 exhibited initiating GalT activity whereas SCG2 showed both initiating and elongating GalT activity. However, the activity of SCG2 was context-dependent, being largely silent in its normal genomic milieu, and different strains show considerable variation in the extent of LPG galactosylation. Thus the L. major genome encodes a family of SCGs with varying specificity and activity, and we propose that strain-specific LPG galactosylation patterns reflect differences in their expression. 相似文献