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961.
Rapid induction of matrix production and mechanical strengthening is essential to the development of bio-artificial constructs for repair and replacement of load-bearing connective tissues. Toward this end, we describe the development of a mechanical bioreactor and its application to investigate the influence of cyclic strain on fibroblast proliferation, matrix accumulation, and the mechanical properties of fibroblast-seeded polyurethane constructs (FSPC). Human fibroblasts were cultured in 10% serum-containing conditions within three-dimensional, porous elastomeric substrates under static conditions and a model regime of cyclic strain (10% strain, 0.25 Hz, 8 h/day), with and without ascorbic acid supplementation. After one week, the combination of cyclic strain and ascorbic acid resulted in significantly increased construct elastic modulus (>110%) relative to either condition alone. In contrast, cyclic strain alone was sufficient to stimulate significant increases in fibroblast proliferation. Mechanical strengthening of FSPCs was accompanied by increased type I collagen and fibronectin matrix accumulation and distribution, and significantly increased gene expression for type I collagen, TGFbeta-1, and CTGF. These results suggest that strain-induced conditioning in vitro leads to mechanical strengthening of fibroblast/material constructs, most likely resulting from increased collagen matrix deposition, secondary to strain-induced increases in cytokine production. 相似文献
962.
The leafminer Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) is a worldwide pest of ornamental and vegetable crops. The most promising nonchemical approach for controlling Liriomyza leafminers in greenhouses is regular releases of the parasitoid Diglyphus isaea (Walker) (Hymenoptera: Eulophidae). In the current study, we examine the hypothesis that the use of D. isaea for biological control of leafminers in greenhouse crops may be more practical and efficient when supplemented with additional control strategies, such as the sterile insect technique (SIT). In small cages, our SIT experiments suggest that release of sterile L. trifolii males in three sterile-to-fertile male ratios (3:1, 5:1, and 10:1) can significantly reduce the numbers of the pest offspring. In large cage experiments, when both parasitoids and sterile males were released weekly, the combined methods significantly reduced mine production and the adult leafminer population size. Moreover, a synergistic interaction effect between these two methods was found, and a model based on our observed data predicts that because of this effect, only the use of both methods can eradicate the pest population. Our study indicates that an integrated pest management approach that combines the augmentative release of the parasitoid D. isaea together with sterile leafminer males is more efficient than the use of either method alone. In addition, our results validate previous theoretical models and demonstrate synergistic control with releases of parasitoids and sterile insects. 相似文献
963.
von Scheven G Alvares LE Mootoosamy RC Dietrich S 《Development (Cambridge, England)》2006,133(14):2731-2745
Recent knockout experiments in the mouse generated amazing craniofacial skeletal muscle phenotypes. Yet none of the genes could be placed into a molecular network, because the programme to control the development of muscles in the head is not known. Here we show that antagonistic signals from the neural tube and the branchial arches specify extraocular versus branchiomeric muscles. Moreover, we identified Fgf8 as the branchial arch derived signal. However, this molecule has an additional function in supporting the proliferative state of myoblasts, suppressing their differentiation, while a further branchial arch derived signal, namely Bmp7, is an overall negative regulator of head myogenesis. 相似文献
964.
Roy Watling 《Mycoscience》2006,47(1):18-24
Those fungi that have been linked to the gasteroid genus Scleroderma by molecular techniques are discussed in relation to secondary metabolites, development, spore morphology, and anatomy. The
group contains epigeous and hypogeous components and sequestrate and boletoid members. An intratribal classification is proposed
to accommodate these life forms. 相似文献
965.
The recognition and rapid degradation of mRNAs with premature translation termination codons by the nonsense-mediated pathway of mRNA decay is an important RNA quality control system in eukaryotes. In mammals, the efficient recognition of these mRNAs is dependent upon exon junction complex proteins deposited on the RNA during pre-mRNA splicing. In yeast, splicing does not play a role in recognition of mRNAs that terminate translation prematurely, raising the possibility that proteins deposited during alternative pre-mRNA processing events such as 3' end formation might contribute to the distinction between normal and premature translation termination. We have utilized mRNAs with a 3' poly(A) tail generated by ribozyme cleavage to demonstrate that the normal process of 3' end cleavage and polyadenylation is not required for mRNA stability or the detection of a premature stop codon. Thus, in yeast, the distinction between normal and premature translation termination events is independent of both splicing and conventional 3' end formation. 相似文献
966.
Regulation of bacterial virulence by two-component systems 总被引:1,自引:0,他引:1
In bacteria, two-component systems (TCS) are widely used signal transduction devices which are engaged in a multitude of gene regulatory systems that respond to changing growth conditions. Many pathogenic bacteria encounter different microenvironments during their infectious cycle and their ability to efficiently adapt to different niches inside and outside of their host organisms is frequently mediated by TCSs, which can, therefore, be considered as an essential prerequisite for their pathogenicity. Although significant progress has been made in the elucidation of basic principles of the signal transduction process itself, in many pathogens the contribution of TCS to bacterial virulence is insufficiently recognized. 相似文献
967.
Since its invasion of North America in 2000, the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae) has notably changed the arthropod community of the soybean agroecosystem. The objectives
of this study were to characterize the foliar predatory fauna associated with A. glycines in commercial soybean fields in Québec, Canada, and to evaluate the suitability of A. glycines as prey for three coccinellid species: Harmonia axyridis Pallas, Propylea quatuordecimpunctata L. and Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Field surveys showed that several predators responded rapidly to expanding and increasing
populations of the soybean aphid. Coccinellidae were the most important aphidophagous predators observed in 2002 (58.6%) and
2003 (44.8%), with mainly four native and naturalized species co-occurring with the soybean aphid throughout the growing season.
Measurement of fitness parameters under laboratory conditions (survival, development time, longevity, fecundity) indicated
that A. glycines is an excellent prey for the development and reproduction of all three of the coccinellid species studied. The intrinsic
rate of natural increase (rm) was highest for H. axyridis (0.238 d−1), intermediate for P. quatuordecimpunctata (0.215 d−1) and lowest for C. maculata (0.134 d−1). 相似文献
968.
The Influence of Previous Mountain Pine Beetle (Dendroctonus ponderosae) Activity on the 1988 Yellowstone Fires 总被引:1,自引:0,他引:1
We examined the historical record of mountain pine beetle (Dendroctonus ponderosae Hopkins) activity within Yellowstone National Park, Wyoming, for the 25-years period leading up to the 1988 Yellowstone fires
(1963–86) to determine how prior beetle activity and the resulting tree mortality affected the spatial pattern of the 1988
Yellowstone fires. To obtain accurate estimates of our model parameters, we used a Markov chain Monte Carlo method to account
for the high degree of spatial autocorrelation inherent to forest fires. Our final model included three statistically significant
variables: drought, aspect, and sustained mountain pine beetle activity in the period 1972–75. Of the two major mountain pine
beetle outbreaks that preceded the 1988 fires, the earlier outbreak (1972–75) was significantly correlated with the burn pattern,
whereas the more recent one (1980–83) was not. Although regional drought and high winds were responsible for the large scale
of this event, the analysis indicates that mountain pine beetle activity in the mid-1970s increased the odds of burning in
1988 by 11% over unaffected areas. Although relatively small in magnitude, this effect, combined with the effects of aspect
and spatial variation in drought, had a dramatic impact on the spatial pattern of burned and unburned areas in 1988. 相似文献
969.
Tui Ray Indrajit Dutta Prasenjit Saha Sampa Das S.C. Roy 《Plant Cell, Tissue and Organ Culture》2006,85(1):11-21
An efficient micropropagation protocol produced large number of plants of the three elite banana (Musa spp.) cultivars Robusta (AAA), Giant Governor (AAA) and Martaman (AAB) from shoot tip meristem. The genetic relationships
and fidelity among the cultivars and micropropagated plants as assessed by random amplified polymorphic DNA (RAPD) and inter-simple
sequence repeat (ISSR) markers, revealed three somaclonal variants from Robusta and three from Giant Governor. A total of
5330 RAPD and 2741 ISSR fragments were generated with 21 RAPD and 12 ISSR primers in micropropagated plants. The percentage
of polymorphic loci by RAPD and ISSR were found to be 1.75, 5.08 in Robusta and 0.83, 5.0 in Giant Governor respectively.
Among the two marker systems used, ISSR fingerprinting detected more polymorphism than RAPD in Robusta and Giant Governor
with most of the primers showing similar fingerprinting profile, whereas Martaman revealed complete genetic stability. 相似文献
970.
van der Heijden MG Bakker R Verwaal J Scheublin TR Rutten M van Logtestijn R Staehelin C 《FEMS microbiology ecology》2006,56(2):178-187
Symbiotic interactions are thought to play a key role in ecosystems. Empirical evidence for the impact of symbiotic bacteria on plant communities is, however, extremely scarce because of experimental constraints. Here, in three complementary experiments, we show that nitrogen-fixing rhizobia bacteria act as a determinant of plant community structure and diversity. Grassland microcosms inoculated with a mixture of rhizobia had a higher above-ground plant productivity (+35%), contained more nitrogen (+85%) and had significant higher community evenness (+34%) than control microcosms without rhizobia. Moreover, three of the four studied legume species required rhizobia to successfully coexist with other plant species. In contrast, the growth and survival of three grass and five forb species were not affected by the presence or absence of rhizobia. Finally, our results also showed that the legume species largely relied on symbiotically fixed nitrogen, both in the field and in the microcosms. This indicates that results in the microcosms are indicative for processes occurring in the field. It is concluded that symbiotic interactions between plants and prokaryotes can contribute to plant productivity, plant community structure and acquisition of limiting resources in legume-rich grassland communities. 相似文献