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121.
Mitchell T Lo A Logan MR Lacy P Eitzen G 《American journal of physiology. Cell physiology》2008,295(5):C1354-C1365
The actin cytoskeleton regulates exocytosis in all secretory cells. In neutrophils, Rac2 GTPase has been shown to control primary (azurophilic) granule exocytosis. In this report, we propose that Rac2 is required for actin cytoskeletal remodeling to promote primary granule exocytosis. Treatment of neutrophils with low doses (< or = 10 microM) of the actin-depolymerizing drugs latrunculin B (Lat B) or cytochalasin B (CB) enhanced both formyl peptide receptor- and Ca(2+) ionophore-stimulated exocytosis. Higher concentrations of CB or Lat B, or stabilization of F-actin with jasplakinolide (JP), inhibited primary granule exocytosis measured as myeloperoxidase release but did not affect secondary granule exocytosis determined by lactoferrin release. These results suggest an obligatory role for F-actin disassembly before primary granule exocytosis. However, lysates from secretagogue-stimulated neutrophils showed enhanced actin polymerization activity in vitro. Microscopic analysis showed that resting neutrophils contain significant cortical F-actin, which was redistributed to sites of primary granule translocation when stimulated. Exocytosis and actin remodeling was highly polarized when cells were primed with CB; however, polarization was reduced by Lat B preincubation, and both polarization and exocytosis were blocked when F-actin was stabilized with JP. Treatment of cells with the small molecule Rac inhibitor NSC23766 also inhibited actin remodeling and primary granule exocytosis induced by Lat B/fMLF or CB/fMLF, but not by Ca(2+) ionophore. Therefore, we propose a role for F-actin depolymerization at the cell cortex coupled with Rac-dependent F-actin polymerization in the cell cytoplasm to promote primary granule exocytosis. 相似文献
122.
CTP:phosphocholine cytidylyltransferase (CCT) catalyzes the conversion of phosphocholine and cytidine 5'-triphosphate (CTP) to CDP-choline for the eventual synthesis of phosphatidylcholine (PC). The enzyme is regulated by reversible association with cellular membranes, with the rate of catalysis increasing following membrane association. Two isoforms of CCT appear to be present in higher eukaryotes, including Drosophila melanogaster, which contains the tandem genes Cct1 and Cct2. Before this study, the CCT1 isoform had not been characterized and the cellular location of each enzyme was unknown. In this investigation, the cDNA encoding the CCT1 isoform from D. melanogaster has been cloned and the recombinant enzyme purified and characterized to determine catalytic properties and the effect of lipid vesicles on activity. CCT1 exhibited a V max of 23904 nmol of CDP-choline min (-1) mg (-1) and apparent K m values for phosphocholine and CTP of 2.29 and 1.21 mM, respectively, in the presence of 20 muM PC/oleate vesicles. Cytidylyltransferases require a divalent cation for catalysis, and the cation preference of CCT1 was found to be as follows: Mg (2+) > Mn (2+) = Co (2+) > Ca (2+) = Ni (2+) > Zn (2+). The activity of the enzyme is stimulated by a variety of lipids, including phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, phosphatidylserine, diphosphatidylglycerol, and the fatty acid oleate. Phosphatidylethanolamine and phosphatidic acid, however, did not have a significant effect on CCT1 activity. The cellular location of both CCT1 and CCT2 isoforms was elucidated by expressing green fluorescent fusion proteins in cultured D. melanogaster Schneider 2 cells. CCT1 was identified as the nuclear isoform, while CCT2 is cytoplasmic. 相似文献
123.
Motojiro Yoshihara Alexander W. Ensminger J. Troy Littleton 《Functional & integrative genomics》2001,1(4):235-240
The sequencing and annotation of the euchromatin of the Drosophila melanogaster genome provides an important foundation that allows neurobiologists to work back from the complete gene set of neuronal proteins
to an eventual understanding of how they function to produce cognition and behavior. Here we provide a brief survey of some
of the key insights that have emerged from analyzing the complete gene set in Drosophila. Not surprisingly, both the Caenorhabditis elegans and Drosophila genomes contain a conserved repertoire of neuronal signaling proteins that are also present in mammals. This includes a large
number of neuronal cell adhesion receptors, synapse-organizing proteins, ion channels and neurotransmitter receptors, and
synaptic vesicle-trafficking proteins. In addition, there are a significant number of fly homologs of human neurological disease
loci, suggesting that Drosophila is likely to be an important disease model for human neuropathology in the near future. The experimental analysis of the Drosophila neuronal gene set will provide important insights into how the nervous system functions at the cellular level, allowing the
field to integrate this information into the framework of ultimately understanding how neuronal ensembles mediate cognition
and behavior.
Electronic Publication 相似文献
124.
Bacteriophage Latent-Period Evolution as a Response to Resource Availability 总被引:11,自引:3,他引:8 下载免费PDF全文
Bacteriophages (phages) modify microbial communities by lysing hosts, transferring genetic material, and effecting lysogenic conversion. To understand how natural communities are affected it is important to develop predictive models. Here we consider how variation between models—in eclipse period, latent period, adsorption constant, burst size, the handling of differences in host quantity and host quality, and in modeling strategy—can affect predictions. First we compare two published models of phage growth, which differ primarily in terms of how they model the kinetics of phage adsorption; one is a computer simulation and the other is an explicit calculation. At higher host quantities (~108 cells/ml), both models closely predict experimentally determined phage population growth rates. At lower host quantities (107 cells/ml), the computer simulation continues to closely predict phage growth rates, but the explicit model does not. Next we concentrate on predictions of latent-period optima. A latent-period optimum is the latent period that maximizes the population growth of a specific phage growing in the presence of a specific quantity and quality of host cells. Both models predict similar latent-period optima at higher host densities (e.g., 17 min at 108 cells/ml). At lower host densities, however, the computer simulation predicts latent-period optima that are much shorter than those suggested by explicit calculations (e.g., 90 versus 1,250 min at 105 cells/ml). Finally, we consider the impact of host quality on phage latent-period evolution. By taking care to differentiate latent-period phenotypic plasticity from latent-period evolution, we argue that the impact of host quality on phage latent-period evolution may be relatively small. 相似文献
125.
Allen Harmsen Kimberley Kusser Louise Hartson Michael Tighe Mary Jean Sunshine Jonathon D Sedgwick Yongwon Choi Dan R Littman Troy D Randall 《Journal of immunology (Baltimore, Md. : 1950)》2002,168(3):986-990
Peyer's patch and nasal-associated lymphoid tissue (NALT) are mucosal lymphoid tissues that appear similar in structure and function. Surprisingly, we found that NALT, unlike Peyer's patch, was formed independently of lymphotoxin (LT)alpha. Furthermore, using mice deficient in the retinoic acid receptor-related orphan receptor-gamma, we found that NALT was formed in the absence of CD4+CD3- cells, which are thought to be the embryonic source of LTalpha. However, we also found that NALT of LTalpha-/- animals was disorganized and lymphopenic, suggesting that the organization and recruitment of lymphocytes within NALT remained dependent on LTalpha. Finally, we demonstrated that both the structure and function of NALT were restored in LTalpha-/- animals upon reconstitution with normal bone marrow. These results demonstrate that the organogenesis of NALT occurs through unique mechanisms. 相似文献
126.
127.
Richard J. Mills Sean J. Humphrey Patrick R.J. Fortuna Mary Lor Simon R. Foster Gregory A. Quaife-Ryan Rebecca L. Johnston Troy Dumenil Cameron Bishop Rajeev Rudraraju Daniel J. Rawle Thuy Le Wei Zhao Leo Lee Charley Mackenzie-Kludas Neda R. Mehdiabadi Christopher Halliday Dean Gilham James E. Hudson 《Cell》2021,184(8):2167-2182.e22
128.
129.
Syntrichia ruralis is a cosmopolitan moss that occupies steep environmental gradients. In arid to semi-arid regions of the world it is a key component of biological soil crusts, which are fundamental to healthy dryland ecosystem processes. As such, S. ruralis has attracted the attention of conservationists seeking to restore degraded biological soil crust communities and their associated vascular flora. Here, we generate genomic data for S. ruralis populations that span climatic gradients across the Colorado Plateau of the southwestern USA to investigate the contributions of neutral and deterministic processes to the partitioning of genomic structure. Although S. ruralis appears to be highly dispersible, geographic proximity significantly predicts genomic similarity. In addition, even when taking into account apparently high migration rates among populations and spatial autocorrelation of allele frequencies, some genomic variation is explained by environmental gradients correlated with elevation and latitude. Consequently, efforts to restore dryland ecosystems by establishing S. ruralis as a foundation should include strategies to ensure that propagule sources of this moss are environmentally stratified and targeted to the current/future climates of restoration sites. 相似文献
130.