Dependence of endothelial cell growth on substrate-bound fibronectin

A better understanding of the mechanism of adhesion, spreading and proliferation of human endothelial cells (HEC) on polymeric surfaces may lead to the development of vascular prostheses which allow the formation of an endothelial lining on the luminal surface. In the present investigation the interaction of HEC with polyethylene precoated with monoclonal antibodies directed against HEC membrane antigens and against extracellular matrix compounds was studied. F(ab¿)2 fragments of a monoclonal antibody, directed against an endothelial cell membrane antigen, and F(ab')2 fragments of a monoclonal antibody, directed against cellular fibronectin, were also included in this study. Preadsorption of these antibodies and F(ab')2 fragments, including mixtures of antibodies and mixtures of F(ab')2 fragments, resulted in cell adhesion and spreading as well as moderate cell proliferation (or no proliferation) for several days. However, a good proliferation of HEC was only observed on polyethylene precoated with fibronectin or CLB-HEC-FN-140 (directed against fibronectin). These results strongly suggest that fibronectin, bound to a solid substrate, provides a biochemical signal necessary for the proliferation of HEC. The initial proliferation of HEC on other preadsorbed antibodies or F(ab')2 fragments may be explained by the fact that suspended HEC, used for cell seeding, still possess cell membrane-bound fibronectin

The role of cellular fibronectin in the interaction of human endothelial cells with polymers

During in-vitro adhesion, spreading and proliferation of human endothelial cells (HEC) on tissue culture polystyrene (TCPS), cellular fibronectin is deposited onto the surface of TCPS in spite of the fact that relatively large amounts of proteins have been adsorbed from the serum-containing culture medium to this surface. Evidence is presented that serum proteins, adsorbed to the TCPS surface, are displaced by cellular fibronectin. In addition, the interaction of HEC with polyethylene, precoated with monoclonal antibodies directed against HEC membrane antigens and against extracellular matrix compounds, was studied. F(ab')2 fragments of two monoclonal antibodies were also included in this study. Preadsorption of these antibodies and F(ab')2 fragments resulted in cell adhesion and spreading as well as moderate cell proliferation (or no proliferation) for several days. A good cell proliferation of HEC was only observed on polyethylene precoated with fibronectin or an antibody directed against fibronectin. The results indicate that the direct or indirect deposition of fibronectin is a prerequisite for the proliferation of HEC. It is suggested that fibronectin, bound to a solid substrate, provides a biochemical signal necessary for the proliferation of HEC

A Solvable Model of Secondary Structure Formation in Random Hetero-Polymers

We propose and solve a simple model describing secondary structure formation in random hetero-polymers. It describes monomers with a combination of one-dimensional short-range interactions (representing steric forces and hydrogen bonds) and infinite range interactions (representing polarity forces). We solve our model using a combination of mean field and random field techniques, leading to phase diagrams exhibiting second-order transitions between folded, partially folded and unfolded states, including regions where folding depends on initial conditions. Our theoretical results, which are in excellent agreement with numerical simulations, lead to an appealing physical picture of the folding process: the polarity forces drive the transition to a collapsed state, the steric forces introduce monomer specificity, and the hydrogen bonds stabilise the conformation by damping the frustration-induced multiplicity of states.Comment: 24 pages, 14 figure

Farmers on film in the fight against striga

With the widespread scaling back of agricultural extension services in Africa, those with a responsibility to deliver information to rural communities are learning to follow new channels. In West Africa, the International Crops Research Institute for the Semi Arid Tropics (ICRISAT) has built on experiences gained by the Africa Rice Center (AfricaRice) in developing a series of ten farmer-to-farmer videos. The ten films are now being widely shown to support rural learning on practical and affordable ways to control one of Africa's most serious weeds - striga..

Survey propagation for the cascading Sourlas code

We investigate how insights from statistical physics, namely survey propagation, can improve decoding of a particular class of sparse error correcting codes. We show that a recently proposed algorithm, time averaged belief propagation, is in fact intimately linked to a specific survey propagation for which Parisi's replica symmetry breaking parameter is set to zero, and that the latter is always superior to belief propagation in the high connectivity limit. We briefly look at further improvements available by going to the second level of replica symmetry breaking.Comment: 14 pages, 5 figure

The low-energy forms of photosystem I light-harvesting complexes: Spectroscopic properties and pigment-pigment interaction characteristics

In this work the spectroscopic properties of the special low-energy absorption bands of the outer antenna complexes of higher plant Photosystem I have been investigated by means of low-temperature absorption, fluorescence, and fluorescence line-narrowing experiments. It was found that the red-most absorption bands of Lhca3, Lhca4, and Lhca1-4 peak, respectively, at 704, 708, and 709 nm and are responsible for 725-, 733-, and 732-nm fluorescence emission bands. These bands are more red shifted compared to "normal" chlorophyll a (Chl a) bands present in light-harvesting complexes. The low-energy forms are characterized by a very large bandwidth (400-450 c

Effect of diammonium phosphate application on strigolactone production and Striga hermonthica infection in three sorghum cultivars

Striga hermonthica infection poses a major constraint to sorghum production in sub-Saharan Africa, and low soil fertility aggravates the S. hermonthica problem. Under mineral nutrient deficiency, the sorghum host secretes large quantities of strigolactones, signalling molecules, into the rhizosphere. These induce S. hermonthica seed germination and subsequent infection of the host roots. In a combination of field and glasshouse experiments, we analysed the effect of microdose applied diammonium hydrogen phosphate (DAP) fertiliser on production of strigolactones, S. hermonthica infection and yield of three different African sorghum genotypes (CGM-19/1-1, Lina-3, DouaG). The sorghum cultivars all produced the strigolactones sorgomol and 5-deoxystrigol, albeit in different quantity and ratio. Without fertiliser, high S. hermonthica infection and emergence occurred under both glasshouse and field conditions. DAP application reduced secretion of sorgomol and 5-deoxystrigol and reduced S. hermonthica germination (66–70%), emergence (49–73%) and dry biomass (90–96%) under glasshouse conditions. Under field conditions, DAP microdosing reduced S. hermonthica emergence by 40–84% and increased sorghum grain yield by 47–142%. Thus DAP application reduced secretion of strigolactones into the rhizosphere and S. hermonthica parasitism both under controlled and field conditions. Microdosing of DAP may prove to be an efficient and cost effective option to reduce S. hermonthica damage in sorghum in sub-Saharan Africa, particularly in combination with other control options, such as intercropping, use of organic fertiliser and hand pulling of S. hermonthica at flowering to achieve integrated S. hermonthica management

Critical Noise Levels for LDPC decoding

We determine the critical noise level for decoding low density parity check error correcting codes based on the magnetization enumerator (\cM), rather than on the weight enumerator (\cW) employed in the information theory literature. The interpretation of our method is appealingly simple, and the relation between the different decoding schemes such as typical pairs decoding, MAP, and finite temperature decoding (MPM) becomes clear. In addition, our analysis provides an explanation for the difference in performance between MN and Gallager codes. Our results are more optimistic than those derived via the methods of information theory and are in excellent agreement with recent results from another statistical physics approach.Comment: 9 pages, 5 figure

Long-term management of Striga hermonthica: strategy evaluation with a spatio-temporal population model

The parasitic weed Striga hermonthica poses a serious threat to cereal production in sub-Saharan Africa. Striga hermonthica seedbanks are long-lived; therefore, long-term effects of control strategies on the seedbank only emerge after several years. We developed a spatially explicit, stochastic model to study the effectiveness of control strategies in preventing invasion of S. hermonthica into previously uninfested fields and in reducing established infestations. Spatial expansion of S. hermonthica and decrease in millet yield in a field was slower, on average, when stochasticity of attachment of seedlings to the host was included and compared to the deterministic model. The spatial patterns of emerged S. hermonthica plants 4–7 years after point inoculation (e.g. seeds in a dung patch) in the spatial-stochastic model resembled the distribution typically observed in farmers fields. Sensitivity analysis showed that only three out of eight life cycle parameters were of minor importance for seedbank dynamics and millet yield. Weeding and intercropping millet with sesame or cowpea reduced the seedbank in the long term, but rotations of millet with trap crops did not. High seedbank replenishment during years of millet monoculture was not sufficiently offset by seedbank depletion in years of trap crop cultivation. Insight from simulations can be employed in a participatory learning context with farmers to have an impact on S. hermonthica control in practice

The link between market orientation and performance in the Australian public sector

Marketing academics and practitioners assume a direct link between market orientation and performance and argue that this applies to both business and non-business organisations. While this aspect has been studied in the business sector, this paper discusses the concepts of market orientation and performance and investigates this relationship in the Australian public sector. The conceptualization of market orientation used is that by Jaworski and Kohli (1993) on which basis MARKOR was developed. This instrument together with an instrument to measure the perceptions of performance of senior managers in the Australian public sector are used to investigate the hypothesized link. The findings confirm a positive relationship between market orientation and performance. The size and type of public sector organisation involved are also found to affect the levels of market orientation together with its components and performance. From the findings, implication are drawn and directions for future research discussed.peer-reviewe