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排序方式: 共有369条查询结果,搜索用时 171 毫秒
41.
42.
Andrew R. Miller Gregory L. Davis Z. Maria Oden Mohamad Reza Razavi Abolfazl Fateh Morteza Ghazanfari Farid Abdolrahimi Shahin Poorazar Fatemeh Sakhaie Randall J. Olsen Ahmad Reza Bahrmand Mark C. Pierce Edward A. Graviss Rebecca Richards-Kortum 《PloS one》2010,5(8)
This study describes the design and evaluation of a portable bright-field and fluorescence microscope that can be manufactured for $240 USD. The microscope uses a battery-operated LED-based flashlight as the light source and achieves a resolution of 0.8 µm at 1000× magnification in fluorescence mode. We tested the diagnostic capability of this new instrument to identify infections caused by the human pathogen, Mycobacterium tuberculosis. Sixty-four direct, decontaminated, and serially diluted smears were prepared from sputa obtained from 19 patients suspected to have M. tuberculosis infection. Slides were stained with auramine orange and evaluated as being positive or negative for M. tuberculosis with both the new portable fluorescence microscope and a laboratory grade fluorescence microscope. Concordant results were obtained in 98.4% of cases. This highly portable, low cost, fluorescence microscope may be a useful diagnostic tool to expand the availability of M. tuberculosis testing at the point-of-care in low resource settings. 相似文献
43.
Endothelial-derived angiocrine signals induce and sustain regenerative lung alveolarization 总被引:1,自引:0,他引:1
Ding BS Nolan DJ Guo P Babazadeh AO Cao Z Rosenwaks Z Crystal RG Simons M Sato TN Worgall S Shido K Rabbany SY Rafii S 《Cell》2011,147(3):539-553
To identify pathways involved in adult lung regeneration, we employ a unilateral pneumonectomy (PNX) model that promotes regenerative alveolarization in the remaining intact lung. We show that PNX stimulates pulmonary capillary endothelial cells (PCECs) to produce angiocrine growth factors that induce proliferation of epithelial progenitor cells supporting alveologenesis. Endothelial cells trigger expansion of cocultured epithelial cells, forming three-dimensional angiospheres reminiscent of alveolar-capillary sacs. After PNX, endothelial-specific inducible genetic ablation of Vegfr2 and Fgfr1 in mice inhibits production of MMP14, impairing alveolarization. MMP14 promotes expansion of epithelial progenitor cells by unmasking cryptic EGF-like ectodomains that activate the EGF receptor (EGFR). Consistent with this, neutralization of MMP14 impairs EGFR-mediated alveolar regeneration, whereas administration of EGF or intravascular transplantation of MMP14(+) PCECs into pneumonectomized Vegfr2/Fgfr1-deficient mice restores alveologenesis and lung inspiratory volume and compliance function. VEGFR2 and FGFR1 activation in PCECs therefore increases MMP14-dependent bioavailability of EGFR ligands to initiate and sustain alveologenesis. 相似文献
44.
A comprehensive study based on gland and seed micromorphology in Euphorbia (Euphorbiaceae) for species distributed in Iranian highlands is presented. A total of 86 species were studied. The gland structure was examined by direct field observations. Taxonomically important characters of glands were observed and measured: size, texture, shape, color, and horns. For species out of Iran herbarium materials were studied. Seed characteristics were examined using scanning electron microscopy (SEM) as well as dissecting light microscopy. Significant features are: seed size, seed shape, presence of caruncle, shape of caruncle, and seed surface ornamentation. A phylogenetic study using Maximum Parsimony (MP) and Bayesian Inference (BI) was performed based on sequences of nuclear DNA internal transcribed spacers (ITS) for selected species representing the main clades known in Euphorbia and with special focus on the species distributed in Iranian highlands. ITS sequences for 20 accessions representing 19 species are provided for the first time, and 48 accessions of 47 species were used from GenBank. The topologies of both analyses were congruent. The results indicate: (1) four main clades with high supports in subgen. Esula which are appropriate to be recognized at sectional rank. (2) E. larica is nested within clade A including few members of subgen. Rhizanthium and is closely related to sect. Balsamis, which is suggested here to be transferred from subgen. Esula into subgen. Rhizanthium. (3) E. osyridea of the monotypic subsect. Osyrideae is closely related to E. buhsei and to the members of sect. Esula. Tracing morphological characters on the phylogenetic tree shows that several morphological characters, such as seed ornamentation applied in previous subgeneric classification of the subgen. Esula, are homoplasious, but the gland structure and capsule surface characters are more reliable for classification purposes. 相似文献
45.
Thayyullathil F Chathoth S Shahin A Kizhakkayil J Hago A Patel M Galadari S 《Journal of cellular biochemistry》2011,112(4):1138-1153
Sphingosine (SPH) is an important bioactive lipid involved in mediating a variety of cell functions including apoptosis. However, the signaling mechanism of SPH-induced apoptosis remains unclear. We have investigated whether SPH inhibits survival signaling in cells by inhibiting Akt kinase activity. This study demonstrates that treatment of Jurkat cells with SPH leads to Akt dephosphorylation as early as 15 min, and the cells undergo apoptosis after 6 h. This Akt dephosphorylation is not mediated through deactivation of upstream kinases, since SPH does not inhibit the upstream phosphoinositide-dependent kinase 1 (PDK1) phosphorylation. Rather, sensitivity to the Ser/Thr protein phosphatase inhibitors (calyculin A, phosphatidic acid, tautomycin, and okadaic acid) indicates an important role for protein phosphatase 1 (PP1) in this process. In vitro phosphatase assay, using Akt immunoprecipitate following treatment with SPH, reveals an increase in Akt-PP1 association as determined by immunoprecipitation analysis. Moreover, SPH-induced dephosphorylation of Akt at Ser(473) subsequently leads to the activation of GSK-3β, caspase 3, PARP cleavage, and ultimately apoptosis. Pre-treatment with caspase 3 inhibitor z-VAD-fmk and Ser/Thr phosphatase inhibitor abrogates the effect of SPH on facilitating apoptosis. Altogether, these results demonstrate that PP1-mediated inhibition of the key anti-apoptotic protein, Akt, plays an important role in SPH-mediated apoptosis in Jurkat cells. 相似文献
46.
Variations in seed micromorphology of 64 taxa of Arenaria and allied genera were examined using scanning electron microscopy (SEM) in order to evaluate their diagnostic value for systematic studies in the genus and providing additional evidence on delimitation of natural groups. Significant diversity was found in seed coat morphology both among and within genera. Size, color, and shape of seeds appear to be of low importance at species level but provide useful evidence at generic rank. Cerastium and Stellaria are well distinguished from Arenaria by serrate seed margins and solid columellae on testa cells. The sculpturing pattern renders most characters potentially applicable in taxonomy and phylogeny assessment in Arenaria. The studied taxa show four basic types of sculpturing, viz. colliculate, rugose, papillate, and smooth. The colliculate type which is characteristic for the core group of Arenaria (A. subg. Arenaria) can be further divided into five subtypes. The smooth seed surface with indistinct cell boundaries represents a synapomorphy for A. subg. Leiosperma, whereas the winged seeds along with rugose surface characterize subg. Odontostemma. Otherwise seed micromorphology rarely provides adequate evidence for separation of natural groups, especially at sectional rank. We hypothesize that the seeds are highly polymorphic in certain groups of taxa showing recent adaptive radiation, such as the annual species of Arenaria, and do not provide strong support for natural groups within the genus. 相似文献
47.
Nusrat Shahin Qureshi Tobias Matzel Erhan Can Cetiner Robbin Schnieders Hendrik R A Jonker Harald Schwalbe Boris Fürtig 《Nucleic acids research》2021,49(13):7753
The ribosomal S1 protein (rS1) is indispensable for translation initiation in Gram-negative bacteria. rS1 is a multidomain protein that acts as an RNA chaperone and ensures that mRNAs can bind the ribosome in a single-stranded conformation, which could be related to fast recognition. Although many ribosome structures were solved in recent years, a high-resolution structure of a two-domain mRNA-binding competent rS1 construct is not yet available. Here, we present the NMR solution structure of the minimal mRNA-binding fragment of Vibrio Vulnificus rS1 containing the domains D3 and D4. Both domains are homologues and adapt an oligonucleotide-binding fold (OB fold) motif. NMR titration experiments reveal that recognition of miscellaneous mRNAs occurs via a continuous interaction surface to one side of these structurally linked domains. Using a novel paramagnetic relaxation enhancement (PRE) approach and exploring different spin-labeling positions within RNA, we were able to track the location and determine the orientation of the RNA in the rS1–D34 bound form. Our investigations show that paramagnetically labeled RNAs, spiked into unmodified RNA, can be used as a molecular ruler to provide structural information on protein-RNA complexes. The dynamic interaction occurs on a defined binding groove spanning both domains with identical β2-β3-β5 interfaces. Evidently, the 3′-ends of the cis-acting RNAs are positioned in the direction of the N-terminus of the rS1 protein, thus towards the 30S binding site and adopt a conformation required for translation initiation. 相似文献
48.
Camilla Godlee Ondrej Cerny Mei Liu Samkeliso Blundell Alanna E. Gallagher Meriam Shahin David W. Holden 《PLoS pathogens》2022,18(5)
SteD is a transmembrane effector of the Salmonella SPI-2 type III secretion system that inhibits T cell activation by reducing the amounts of at least three proteins –major histocompatibility complex II (MHCII), CD86 and CD97 –from the surface of antigen-presenting cells. SteD specifically localises at the trans-Golgi network (TGN) and MHCII compartments; however, the targeting, membrane integration and trafficking of SteD are not understood. Using systematic mutagenesis, we identify distinct regions of SteD that are required for these processes. We show that SteD integrates into membranes of the ER/Golgi through a two-step mechanism of membrane recruitment from the cytoplasm followed by integration. SteD then migrates to and accumulates within the TGN. From here it hijacks the host adaptor protein (AP)1-mediated trafficking pathway from the TGN to MHCII compartments. AP1 binding and post-TGN trafficking require a short sequence in the N-terminal cytoplasmic tail of SteD that resembles the AP1-interacting dileucine sorting signal, but in inverted orientation, suggesting convergent evolution. 相似文献
49.
Functional and specific receptors for vasoactive intestinal peptide (VIP) (determined by their capacity to bind 125I-VIP and activate adenylate cyclase) and cyclic AMP-dependent phosphodiesterase activities were characterized in enterocytes of human fetal small intestine between 18 and 23 weeks of gestation. Half-maximal stimulation of the cyclase and inhibition of 125I-VIP binding in membrane preparations were respectively observed at 1.4 and 5 × 10−10 M VIP. The peptides structurally related to VIP activated the cyclic AMP generating system at pharmacological doses (10−7M and above) in the following order of potency: VIP> PHI> GRF> secretin. Other peptides or test substances, including GIP, pancreatic glucagon, somatostatin-14, gastrin, CCK, neurotensin, pancreatic polypeptide, PYY, substance P, histamine and isoproterenol are inactive in this system, while the ubiquitous adenylate cyclase activators NaF, forskolin and prostaglandins were effective. These results, combined with the appearance of intestinal VIP in nerve fibers at 8 weeks and with the morphological and enzymatic maturation at 9–12 weeks of the intestinal mucosa, indicate that this neuropeptide may regulate either the differentiation or function of enterocytes during the early development of human intestinal mucosa. 相似文献
50.