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971.
We examined the relationship between pond duration and life history characters of the clam shrimp Eulimnadia texana, a species
inhabiting ephemeral ponds in southwestern North America. Since the shrimp live in temporary habitats, we predicted that there
should be high selection pressure on life history characteristics associated with rapid development (e.g., fast growth, early
maturity, etc.), rather than selection for increased longevity. Pond duration was estimated using a combination of average
monthly rainfall and pond size (surface to volume ratio). Shrimp that live in smaller ponds (high surface to volume ratio)in
areas with low average rainfall should, on average, experience a shorter total time available for development than those in
larger ponds or in areas of higher rainfall. These shrimp should have an earlier age at maturity, reduced longevity, lower
fecundity, and faster growth. Five replicate populations of clam shrimp were collected as cysts from five ponds. These shrimp
were raised in a common garden experiment in the laboratory. Daily measurements of growth and egg production were taken and
ages at maturity and death were recorded. Shrimp from areas with higher average rainfall had slower growth, higher fecundity,
greater longevity, and an earlier age at maturity than those from areas with lower average rainfall. If average rainfall is
an accurate measure of pond duration, then the first three of these life history traits differ in the directions expected.
However, age at maturity varied in a manner opposite to that expected, being earlier in the ponds with longer duration. Surface
to volume ratio was not helpful in further resolving differences in these life history characters.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
972.
Inhibition of the High-Affinity Brain Glutamate Transporter GLAST-1 via Direct Phosphorylation 总被引:10,自引:5,他引:5
Abstract: Neurotransmission at excitatory glutamatergic synapses is terminated by the reuptake of the neurotransmitter by high-affinity transporters, which keep the extracellular glutamate concentration below excitotoxic levels. The amino acid sequence of the recently isolated and cloned brain-specific glutamate/aspartate transporter (GLAST-1) of the rat reveals three consensus sequences of putative phosphorylation sites for protein kinase C (PKC). The PKC activator phorbol 12-myristate 13-acetate (PMA) decreased glutamate transport activity in Xenopus oocytes and human embryonic kidney cells (HEK293) expressing the cloned GLAST-1 cDNA, within 20 min, to 25% of the initial transport activity. This down-regulation was blocked by the PKC inhibitor staurosporine. GLAST-1 transport activity remains unimpaired by phorbol 12-monomyristate. Removal of all putative PKC sites of wild-type GLAST-1 by site-directed mutagenesis did not abolish inhibition of glutamate transport. [32 P]Phosphate-labeled wild-type and mutant transport proteins devoid of all predicted PKC sites were detected by immunoprecipitation after stimulation with PMA. Immunoprecipitation of [35 S]methionine-labeled transporter molecules indicates a similar stability of phosphorylated and nonphosphorylated GLAST-1 protein. Immunofluorescence staining did not differentiate surface staining of HEK293 cells expressing GLAST-1 with and without PMA treatment. These data suggest that the neurotransmitter transporter activity of GLAST-1 is inhibited by phosphorylation at a non-PKC consensus site. 相似文献
973.
Human T cells recovered from human/Balb radiation chimeras are hypersensitive to human immunodeficiency virus type 1 infection. 下载免费PDF全文
O Shapira-Nahor H Marcus H Segall I Lubin S Slavin A Panet Y Reisner 《Journal of virology》1997,71(6):4495-4501
Replication of human immunodeficiency virus type 1 (HIV-1) is regulated by virus-encoded regulatory proteins, as well as by a variety of cellular factors. Productive infection of human T lymphocytes by HIV-1 is dependent upon the activation status of the target cells. In general, short-term mitogenic stimulation of CD4 T cells is used to enhance infection of peripheral blood mononuclear cells (PBMC) in vitro. Recently, we demonstrated that adoptive transfer of human PBMC into lethally irradiated BALB/c mice, radioprotected with severe combined immunodeficiency (SCID) mouse bone marrow, leads to marked T-cell activation and proliferation. In the present study, we investigated the effect of such xenoactivation of human T cells on their susceptibility to HIV-1 infection. Human cells that were recovered from human/Balb radiation chimeras supported efficient replication of laboratory strains of HIV-1, as well as of HIV-1 clinical isolates. The multiplicity of infection required to attain effective virus replication in the recovered xenoactivated human cells was 10- to 100-fold lower than that needed for infection of short- or long-term phytohemagglutinin (PHA)-stimulated blasts or of various T-cell lines. Analysis of human cell surface activation markers has indicated that xenoactivation in the mouse, in contrast to in vitro stimulation with PHA, is associated with a marked downregulation of CD25 (interleukin 2 receptor). Our results demonstrate that human cells recovered from human/Balb radiation chimeras, which are hypersensitive to HIV-1 infection, differ from in vitro-stimulated cells in their activation status. Therefore, this system could be used to study host factors that participate in HIV-1 infection and replication in vitro and in vivo. 相似文献
974.
Pathways of glycosphingolipid biosynthesis in SW13 cells in the presence and absence of vimentin intermediate filaments 总被引:2,自引:2,他引:0
We reported previously that the incorporation of sugars intoglycosphingolipids (GSL) is diminished in SW13 cells that lacka vimentin intermediate filament (IF) network (vim) comparedto vim+ cells. To further analyze the nature of this abnormality,we double-labeled cells with 3H-serine and l4C-sugars. Therewas no difference between vim+ and vim cells in the incorporationof serine into GSL, although the usual difference in sugar incorporationwas observed. This indicated that the defect in vim cellswas not in the incorporation of sugars into ceramide synthesizedde novo by acylation of sphinganine (pathway 1). Sugars canalso be incorporated into ceramide synthesized from sphingosinethat is derived from catabolism of sphin-golipids (pathway 2),and into GSL that recycle through the Golgi apparatus from endosomes(pathway 3). The amount of galactose and glucosamine incorporatedinto GSL in these three pathways was analyzed by the use oftwo inhibitors of sphingolipid biosynthesis. ß-Chloroala-nineinhibits the de novo synthesis of sphinganine (pathway 1), andfumonisin Bl inhibits the acylation of sphinganine and sphingosine(pathways 1 and 2). We were surprised to observe that in bothvim+ and vim cells only 2040% of sugar incorporationinto GSL took place in pathway 1, and 6080% of sugarincorporation took place in the recycling pathways. Moreover,in contrast to larger GSL, GlcCer was not synthesized in pathway3. Our observations indicate that vimentin IF facilitate therecycling of GSL and sphingosine, and that the differences betweenvim+ and vim cells are predominantly in pathways 2 and3. Furthermore, although it is generally believed that virtuallyall GSL are synthesized in the de novo pathway, these data indicatethat the recyling pathways predominate in the incorporationof sugars into GSL in SW13 cells. glycosphingolipid biosynthesis intermediate filaments SW13 cells sphingolipid recycling vimentin 相似文献
975.
Rodrigo Gaiga Paulino Marcus Vińicius Rezende Dos Santos Mark L Latash Gil Lúcio Almeida 《Journal of electromyography and kinesiology》2005,15(4):406-417
We studied the kinematic and electromyographic (EMG) patterns during single-joint elbow flexion movements with a reversal and tested two hypotheses. First, that the amplitude of the second phase of the movement (M(2)) will be controlled by two different means, a drop in the second flexor burst for a small M(2) and an increase in the integral of the extensor burst for larger M(2). Second, based on the muscle stretch-shortening cycle (SSC), that movements reversing without a delay will show a larger extensor burst, as compared to movements that reverse after a delay. Changes in EMG patterns with M(2) amplitude supported the first hypothesis and could be interpreted within the framework of the equilibrium-point hypothesis. The observations also corroborate a hypothesis that discrete movements represent outcomes of an oscillatory control process stopped at a particular phase. In Experiment-2, even the shortest delay at the target led to a significantly larger extensor burst. However, there were no differences in the peak velocity of M2 with and without the delay. These observations do not support a major role of stretch reflexes in the SSC effects during such movements. However, they are compatible with the idea of peripheral factors, such as peripheral muscle and tendon elasticity, playing a major potentiating role in the SSC. 相似文献
976.
977.
Helena Danielsson Thorell Natascha H Beyer Niels H H Heegaard Marcus Ohman Thomas Nilsson 《European journal of biochemistry》2004,271(17):3539-3546
A detailed comparison between native chlorite dismutase from Ideonella dechloratans, and the recombinant version of the protein produced in Escherichia coli, suggests the presence of a covalent modification in the native enzyme. Although the native and recombinant N- and C-terminal sequences are identical, the enzymes display different electrophoretic mobilities, and produce different peptide maps upon digestion with trypsin and separation of fragments using capillary electrophoresis. Comparison of MALDI mass spectra of tryptic peptides from the native and recombinant enzymes suggests two locations for modification in the native protein. Mass spectrometric analysis of isolated peptides from a tryptic digest of the native enzyme identifies a possible cross-linked dipeptide, suggesting an intrachain cross-link in the parent protein. Spectrophotometric titration of the native enzyme in the denatured state reveals two titrating components absorbing at 295 nm, suggesting the presence of about one tyrosine residue per subunit with an anomalously low pK(a). The EPR spectrum for the recombinant enzyme is different from that of the native enzyme, and contains a substantial contribution of a low-spin species with the characteristics of bis-histidine coordination. These results are discussed in terms of a covalent cross-link between a histidine and a tyrosine sidechain, similar to those found in other heme enzymes operating under highly oxidizing conditions. 相似文献
978.
Biological invasion by a benthivorous fish reduced the cover and species richness of aquatic plants in most lakes of a large North American ecoregion 总被引:1,自引:0,他引:1 下载免费PDF全文
Przemyslaw G. Bajer Marcus W. Beck Timothy K. Cross Justine D. Koch William M. Bartodziej Peter W. Sorensen 《Global Change Biology》2016,22(12):3937-3947
Biological invasions are projected to be the main driver of biodiversity and ecosystem function loss in lakes in the 21st century. However, the extent of these future losses is difficult to quantify because most invasions are recent and confounded by other stressors. In this study, we quantified the outcome of a century‐old invasion, the introduction of common carp to North America, to illustrate potential consequences of introducing non‐native ecosystem engineers to lakes worldwide. We used the decline in aquatic plant richness and cover as an index of ecological impact across three ecoregions: Great Plains, Eastern Temperate Forests and Northern Forests. Using whole‐lake manipulations, we demonstrated that both submersed plant cover and richness declined exponentially as carp biomass increased such that plant cover was reduced to <10% and species richness was halved in lakes in which carp biomass exceeded 190 kg ha?1. Using catch rates amassed from 2000+ lakes, we showed that carp exceeded this biomass level in 70.6% of Great Plains lakes and 23.3% of Eastern Temperate Forests lakes, but 0% of Northern Forests lakes. Using model selection analysis, we showed that carp was a key driver of plant species richness along with Secchi depth, lake area and human development of lake watersheds. Model parameters showed that carp reduced species richness to a similar degree across lakes of various Secchi depths and surface areas. In regions dominated by carp (e.g., Great Plains), carp had a stronger impact on plant richness than human watershed development. Overall, our analysis shows that the introduction of common carp played a key role in driving a severe reduction in plant cover and richness in a majority of Great Plains lakes and a large portion of Eastern Temperate Forests lakes in North America. 相似文献
979.
Network analyses support the role of prey preferences in shaping resource use patterns within five animal populations 下载免费PDF全文
Paula Lemos‐Costa Mathias M. Pires Márcio S. Araújo Marcus A. M. de Aguiar Paulo R. Guimarães Jr. 《Oikos》2016,125(4):492-501
Individual variation is an inherent aspect of animal populations and understanding the mechanisms shaping resource use patterns within populations is crucial to comprehend how individuals partition resources. Theory predicts that differences in prey preferences among consumers and/or differences in the likelihood of adding new resources to their diets are key mechanisms underlying intrapopulation variation in resource use. We developed network models based on optimal diet theory that simulate how individuals consume resources under varying scenarios of individual variation in prey preferences and in the willingness of consuming alternate resources. We then investigated how the structure of individual–resource networks generated under each model compared to the structure of observed networks representing five classical examples of individual diet variation. Our results support the notion that, for the studied populations, individual variation in prey preferences is the major factor explaining patterns in individual–resource networks. In contrast, variation in the willingness of adding prey does not seem to play an important role in shaping patterns of resource use. Individual differences in prey preferences in the studied populations may be generated by complex behavioral rules related to cognitive constraints and experience. Our approach provides a pathway for mapping foraging models into network patterns, which may allow determining the possible mechanisms leading to variation in resource use within populations. 相似文献
980.
Initially investigated as a color formation process in thermally treated foods, nowadays, the relevance of the Maillard reaction in vivo is generally accepted. Many chronic and age-related diseases such as diabetes, uremia, atherosclerosis, cataractogenesis and Alzheimer’s disease are associated with Maillard derived advanced glycation endproducts (AGEs) and α-dicarbonyl compounds as their most important precursors in terms of reactivity and abundance. However, the situation in vivo is very challenging, because Maillard chemistry is paralleled by enzymatic reactions which can lead to both, increases and decreases in certain AGEs. In addition, mechanistic findings established under the harsh conditions of food processing might not be valid under physiological conditions. The present review critically discusses the relevant α-dicarbonyl compounds as central intermediates of AGE formation in vivo with a special focus on fragmentation pathways leading to formation of amide-AGEs. 相似文献