953 resultados para Research formation multireferential
Resumo:
The Ensatina eschscholtzii complex of plethodontid salamanders, a well-known “ring species,” is thought to illustrate stages in the speciation process. Early research, based on morphology and coloration, has been extended by the incorporation of studies of protein variation and mitochondrial DNA sequences. The new data show that the complex includes a number of geographically and genetically distinct components that are at or near the species level. The complex is old and apparently has undergone instances of range contraction, isolation, differentiation, and then expansion and secondary contact. While the hypothesis that speciation is retarded by gene flow around the ring is not supported by molecular data, the general biogeographical hypothesis is supported. There is evidence of a north to south range expansion along two axes, with secondary contact and completion of the ring in southern California. Current research targets regions once thought to show primary intergradation, but which molecular markers reveal to be zones of secondary contact. Here emphasis is on the subspecies E. e. xanthoptica, which is involved in four distinct secondary contacts in central California. There is evidence of renewed genetic interactions upon recontact, with greater genetic differentiation within xanthoptica than between it and some of the interacting populations. The complex presents a full array of intermediate conditions between well-marked species and geographically variable populations. Geographically differentiated segments represent a diversity of depths of time of isolation and admixture, reflecting the complicated geomorphological history of California. Ensatina illustrates the continuing difficulty in making taxonomic assignments in complexes studied during species formation.
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The most productive (“star”) bioscientists had intellectual human capital of extraordinary scientific and pecuniary value for some 10–15 years after Cohen and Boyer’s 1973 founding discovery for biotechnology [Cohen, S., Chang, A., Boyer, H. & Helling, R. (1973) Proc. Natl. Acad. Sci. USA 70, 3240–3244]. This extraordinary value was due to the union of still scarce knowledge of the new research techniques and genius and vision to apply them in novel, valuable ways. As in other sciences, star bioscientists were very protective of their techniques, ideas, and discoveries in the early years of the revolution, tending to collaborate more within their own institution, which slowed diffusion to other scientists. Close, bench-level working ties between stars and firm scientists were needed to accomplish commercialization of the breakthroughs. Where and when star scientists were actively producing publications is a key predictor of where and when commercial firms began to use biotechnology. The extent of collaboration by a firm’s scientists with stars is a powerful predictor of its success: for an average firm, 5 articles coauthored by an academic star and the firm’s scientists result in about 5 more products in development, 3.5 more products on the market, and 860 more employees. Articles by stars collaborating with or employed by firms have significantly higher rates of citation than other articles by the same or other stars. The U.S. scientific and economic infrastructure has been particularly effective in fostering and commercializing the bioscientific revolution. These results let us see the process by which scientific breakthroughs become economic growth and consider implications for policy.
Resumo:
We analyzed the process of inflorescence formation in Impatiens balsamina by studying the architecture of the plant under different photoperiod treatments. Floral reversion under noninductive conditions in this species is caused by the lack of persistence of the induced state in the leaf. This can be used to control the amount of inductive signal and to examine its quantitative influence on morphological changes in the plant. The floral transition was characterized by a continuum of variation at the level of meristem identity, primordium initiation, and floral organ identity. This continuum was enhanced during reversion, suggesting that the establishment of a continuum partly reflects limiting amounts of inductive signal exported from the leaf to the meristem. The transcription patterns of two homologs of genes involved in the control of floral meristem identity, Imp-FLO and Imp-FIM, were similar in terminal and axillary flowers and may be associated with the continuum exhibited by I. balsamina. By analyzing the fate of axillary meristem primordia initiated before and after the beginning of the inductive period, we showed that de novo initiation of axillary meristem primordia by the evoked meristem is not required and that primordia initiated before evocation can adopt different fates, depending on the amount of inductive signal. The influence of age and/or position on primordium responsiveness to the inductive signal is discussed.
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Trichome development is dependent on gibberellin (GA) signaling in Arabidopsis thaliana. Using the GA-deficient mutant ga1–3, the GA-response mutant spy-5, and uniconazol (a GA-biosynthesis inhibitor), we show that the GA level response correlates positively with both trichome number and trichome branch number. Two genes, GL1 and TTG, are required for trichome initiation. In ga1–3, coexpression of GL1 and R, the maize TTG functional homolog, under control of the constitutive 35S promoter, restored trichome development, whereas overexpression of neither GL1 nor R alone was sufficient to significantly suppress the glabrous phenotype. We next focused on GL1 regulation by GAs. In the double mutant the gl1–1 glabrous phenotype is epistatic to the spy-5 phenotype, suggesting that GL1 acts downstream of the GA signal transduction pathway. The activity of a β-glucuronidase reporter gene driven by the GL1 promoter was decreased in the wild type grown on uniconazol and showed a clear GA-dependent activation in ga1–3. Finally, quantification of GL1 transcript levels by reverse transcriptase-polymerase chain reaction demonstrated that relative to wild type, ga1–3 plants contained less transcript. These data support the hypothesis that GAs induce trichome development through up-regulation of GL1 and possibly TTG genes.
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The effects of plant hormones and sucrose (Suc) on potato (Solanum tuberosum L.) tuberization were studied using in vitro cultured single-node cuttings. Tuber-inducing (high Suc) and -noninducing (low Suc or high Suc plus gibberellin [GA]) media were tested. Tuberization frequencies, tuber widths, and stolon lengths were measured during successive stages of development. Endogenous GAs and abscisic acid (ABA) were identified and quantified by high-performance liquid chromatography and gas chromatography-mass spectrometry. Exogenous GA4/7 promoted stolon elongation and inhibited tuber formation, whereas exogenous ABA stimulated tuberization and reduced stolon length. Indoleacetic acid-containing media severely inhibited elongation of stolons and smaller sessile tubers were formed. Exogenous cytokinins did not affect stolon elongation and tuber formation. Endogenous GA1 level was high during stolon elongation and decreased when stolon tips started to swell under inducing conditions, whereas it remained high under noninducing conditions. GA1 levels were negatively correlated with Suc concentration in the medium. We conclude that GA1 is likely to be the active GA during tuber formation. Endogenous ABA levels decreased during stolon and tuber development, and ABA levels were similar under inducing and noninducing conditions. Our results indicate that GA is a dominant regulator in tuber formation: ABA stimulates tuberization by counteracting GA, and Suc regulates tuber formation by influencing GA levels.
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The de-epoxidation of violaxanthin to antheraxanthin (Anth) and zeaxanthin (Zeax) in the xanthophyll cycle of higher plants and the generation of nonphotochemical fluorescence quenching in the antenna of photosystem II (PSII) are induced by acidification of the thylakoid lumen. Dicyclohexylcarbodiimide (DCCD) has been shown (a) to bind to lumen-exposed carboxy groups of antenna proteins and (b) to inhibit the pH-dependent fluorescence quenching. The possible influence of DCCD on the de-epoxidation reactions has been investigated in isolated pea (Pisum sativum L.) thylakoids. The Zeax formation was found to be slowed down in the presence of DCCD. The second step (Anth → Zeax) of the reaction sequence seemed to be more affected than the violaxanthin → Anth conversion. Comparative studies with antenna-depleted thylakoids from plants grown under intermittent light and with unstacked thylakoids were in agreement with the assumption that binding of DCCD to antenna proteins is probably responsible for the retarded kinetics. Analyses of the DCCD-induced alterations in different antenna subcomplexes showed that Zeax formation in the PSII antenna proteins was predominantly influenced by DCCD, whereas Zeax formation in photosystem I was nearly unaffected. Our data support the suggestion that DCCD binding to PSII antenna proteins is responsible for the observed alterations in xanthophyll conversion.
Resumo:
Recently, the biosynthesis of an unusual membrane phospholipid, N-acylphosphatidylethanolamine (NAPE), was found to increase in elicitor-treated tobacco (Nicotiana tabacum L.) cells (K.D. Chapman, A. Conyers-Hackson, R.A. Moreau, S. Tripathy [1995] Physiol Plant 95: 120–126). Here we report that before induction of NAPE biosynthesis, N-acylethanolamine (NAE) is released from NAPE in cultured tobacco cells 10 min after treatment with the fungal elicitor xylanase. In radiolabeling experiments [14C]NAE (labeled on the ethanolamine carbons) increased approximately 6-fold in the culture medium, whereas [14C]NAPE associated with cells decreased approximately 5-fold. Two predominant NAE molecular species, N-lauroylethanolamine and N-myristoylethanolamine, were specifically identified by gas chromatography-mass spectrometry in lipids extracted from culture medium, and both increased in concentration after elicitor treatment. NAEs were found to accumulate extracellularly only. A microsomal phospholipase D activity was discovered that formed NAE from NAPE; its activity in vitro was stimulated about 20-fold by mastoparan, suggesting that NAPE hydrolysis is highly regulated, perhaps by G-proteins. Furthermore, an NAE amidohydrolase activity that catalyzed the hydrolysis of NAE in vitro was detected in homogenates of tobacco cells. Collectively, these results characterize structurally a new class of plant lipids and identify the enzymatic machinery involved in its formation and inactivation in elicitor-treated tobacco cells. Recent evidence indicating a signaling role for NAPE metabolism in mammalian cells (H.H.O. Schmid, P.C. Schmid, V. Natarajan [1996] Chem Phys Lipids 80: 133–142) raises the possibility that a similar mechanism may operate in plant cells.
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We report that silver ion HPLC provides remarkable separations of C27 sterols differing only in the number or location of olefinic double bonds. This technique has been extended to LC-MS, analysis of purified components by GC, GC-MS, and 1H NMR, and to its use on a semipreparative scale. The application of this methodology for the demonstration of the catalysis, by rat liver microsomes, of the conversion of 7-dehydrocholesterol to cholesta-5,8-dien-3 beta-ol is also presented.
Resumo:
How fast can a protein fold? The rate of polypeptide collapse to a compact state sets an upper limit to the rate of folding. Collapse may in turn be limited by the rate of intrachain diffusion. To address this question, we have determined the rate at which two regions of an unfolded protein are brought into contact by diffusion. Our nanosecond-resolved spectroscopy shows that under strongly denaturing conditions, regions of unfolded cytochrome separated by approximately 50 residues diffuse together in 35-40 microseconds. This result leads to an estimate of approximately (1 microsecond)-1 as the upper limit for the rate of protein folding.
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Lipid bodies, cytoplasmic inclusions that develop in cells associated with inflammation, are inducible structures that might participate in generating inflammatory eicosanoids. Cis-unsaturated fatty acids (arachidonic and oleic acids) rapidly induced lipid body formation in leukocytes, and this lipid body induction was inhibited by aspirin and nonsteroidal antiinflammatory drugs (NSAIDs). Several findings indicates that the inhibitory effect of aspirin and NSAIDs on lipid body formation was independent of cyclooxygenase (COX) inhibition. First, the non-COX inhibitor, sodium salicylate, was as potent as aspirin in inhibiting lipid body formation elicited by cis-fatty acids. Second, cis-fatty acid-induced lipid body formation was not impaired in macrophages from COX-1 or COX-2 genetically deficient mice. Finally, NSAIDs inhibited arachidonic acid-induced lipid body formation likewise in macrophages from wild-type and COX-1- and COX-2-deficient mice. An enhanced capacity to generate eicosanoids developed after 1 hr concordantly with cis-fatty acid-induced lipid body formation. Arachidonic and oleic acid-induced lipid body numbers correlated with the enhanced levels of leukotrienes B4 and C4 and prostaglandin E2 produced after submaximal calcium ionophore stimulation. Aspirin and NSAIDs inhibited both induced lipid body formation and the enhanced capacity for forming leukotrienes as well as prostaglandins. Our studies indicate that lipid body formation is an inducible early response in leukocytes that correlates with enhanced eicosanoid synthesis. Aspirin and NSAIDs, independent of COX inhibition, inhibit cis-fatty acid-induced lipid body formation in leukocytes and in concert inhibit the enhanced synthesis of leukotrienes and prostaglandins.
Resumo:
Parathyroid hormone-related peptide (PTHrP) was initially identified as a product of malignant tumors that mediates paraneoplastic hypercalcemia. It is now known that the parathyroid hormone (PTH) and PTHrP genes are evolutionarily related and that the products of these two genes share a common receptor, the PTH/PTHrP receptor. PTHrP and the PTH/PTHrP receptor are widely expressed in both adult and fetal tissues, and recent gene-targeting and disruption experiments have implicated PTHrP as a developmental regulatory molecule. Apparent PTHrP functions include the regulation of endochondral bone development, of hair follicle formation, and of branching morphogenesis in the breast. Herein, we report that overexpression of PTHrP in chondrocytes using the mouse type II collagen promoter induces a novel form of chondrodysplasia characterized by short-limbed dwarfism and a delay in endochondral ossification. This features a delay in chondrocyte differentiation and in bone collar formation and is sufficiently marked that the mice are born with a cartilaginous endochondral skeleton. In addition to the delay, chondrocytes in the transgenic mice initially become hypertrophic at the periphery of the developing long bones rather than in the middle, leading to a seeming reversal in the pattern of chondrocyte differentiation and ossification. By 7 weeks, the delays in chondrocyte differentiation and ossification have largely corrected, leaving foreshortened and misshapen but histologically near-normal bones. These findings confirm a role for PTHrP as an inhibitor of the program of chondrocyte differentiation. PTHrP may function in this regard to maintain the stepwise differentiation of chondrocytes that initiates endochondral ossification in the midsection of endochondral bones early in development and that also permits linear growth at the growth plate later in development.
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In studies of variants of the P(ant) promoter of bacteriophage P22, the Arc protein was found not only to slow the rate at which RNA polymerase forms open complexes but also to accelerate the rate at which the enzyme clears the promoter. These dual activities permit Arc, bound at a single operator subsite, to act as an activator or as a repressor of different promoter variants. For example, Arc activates a P(ant) variant for which promoter clearance is rate limiting in the presence and absence of Arc but represses a closely related variant for which open-complex formation becomes rate limiting in the presence of Arc. The acceleration of promoter clearance by Arc requires occupancy of the operator subsite proximal to the -35 region and is diminished when Arc bears a mutation in Arg-23, a residue that makes a DNA-backbone contact in the operator complex.
Resumo:
The interaction of the hormone erythropoietin and its receptor (EpoR) is though to be required for normal hematopoiesis. To define the role of EpoR in this process, the murine EpoR was disrupted by homologous recombination. Mice lacking the EpoR died in utero at embryonic day 11-12.5 with severe anemia. Embryonic erythropoiesis was markedly diminished, while fetal liver hematopoiesis was blocked at the proerythroblast stage. Other cell types known to express EpoR, including megakaryocytes, mast, and neural cells were morphologically normal. Reverse transcription-coupled PCR analysis of RNA from embryonic yolk sac, peripheral blood, and fetal liver demonstrated near normal transcripts levels for EKLF, thrombopoietin (Tpo), c-MPL, GATA-1, GATA-2, and alpha- and embryonic beta H1-globin but non for adult beta maj-globin. While colony-forming unit-erythroid (CFU-E) and burst-forming unit-erythroid (BFU-E) colonies were not present in cultures derived from EpoR-/- liver or yolk sac cells, hemoglobin-containing BFU-E colonies were detected in cultures treated with recombinant Tpo and Kit ligand or with Tpo and interleukin 3 and 11. Rescued BFU-E colonies expressed adult beta-globin and c-MPL and appeared morphologically normal. Thus, erythroid progenitors are formed in vivo in mice lacking the EpoR, and our studies demonstrate that a signal transmitted through the Tpo receptor c-MPL stimulates proliferation and terminal differentiation of these progenitors in vitro.
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By using a novel, extremely sensitive and specific gas chromatography-mass spectrometry technique we demonstrate in Pinus sylvestris (L.) trees the existence of a steep radial concentration gradient of the endogenous auxin, indole-3-acetic acid, over the lateral meristem responsible for the bulk of plant secondary growth, the vascular cambium. This is the first evidence that plant morphogens, such as indole-3-acetic acid, occur in concentration gradients over developing tissues. This finding gives evidence for a regulatory system in plants based on positional signaling, similar to animal systems.