The evolutionary history of Drosophila buzzatii. XXX. Mitochondrial DNA polymorphism in original and colonizing populations

Both original and colonizer populations of Drosophila buzzatii have been analyzed for mtDNA restriction polymorphisms. Most of the mtDNA nucleotide variation in original populations of NW Argentina can be explained by intrapopulation diversity and only a small fraction can be accounted for by between-population diversity. Similar results are obtained using either the estimated number of nucleotide substitutions per site or considering each restriction site as a locus. Colonizer populations of the Iberian Peninsula are monomorphic and show only the most common haplotype from the original populations. Under the infinite island model and assuming that populations are in equilibrium, fixation indices indicate enough gene flow to explain why the populations are not structured. Yet, the possibility exists that populations have not reached an equilibrium after a founder event at the end of the last Pleistocene glaciation. Tajima's test suggests that directional selection and/or a recent bottleneck could explain the present mtDNA differentiation. Considering the significant population structure found for the chromosomal and some allozyme polymorphisms, the among- population uniformity for mtDNA variability argues in favor of the chromosomal and some allozyme polymorphisms being adaptive.      

A demonstration of asynchronous local cycles in an acarine predator-prey system

Population fluctuations in a continuous predator-prey system consisting of the spider mite,Tetranychus urticae Koch and its predator,Typhlodromus occidentalis Nesbitt, were assessed for almost 2 years (ca. 50 prey generations), on six mini-orchards of young apple trees in a climatically controlled glasshouse. During the first half of the experiment the plants were either connected to each other with dowel rods or unconnected and separate. In the second half, the plants were all connected. Population densities of both prey and predator on the unconnected mini-orchards were always higher than on the connected ones. Within the mini-orchards (=local scale), prey and predator populations go through a pattern of large amplitude cycles which continued throughout the experimental period. At the regional scale (mean over all mini-orchards) two types of fluctuations were observed. Large amplitude fluctuations associated with synchrony of the local cycles and small amplitude fluctuations associated with periods when local population cycles are proceeding out of phase. Transition from synchronous to asynchronous cycles took place very fast (within a few weeks), suggesting a mechanism generating asynchrony and possibly also partial refuges, which in turn trigger stabilising mechanisms at a regional scale. Causes of the synchrony are unclear. They may relate to the application of a pesticide (pirimicarb) used to control aphids, but there may just as well be an indirect form of causation, e.g. whereby the factors that promote aphid outbreaks also promote spider-mite population growth and temporary escape from control by the predators. Despite the synchronising factors the predator-prey system persisted, without external inputs, at a fairly small spatial scale, the size of a small glasshouse. Assessing the spatial scale and heterogeneity whereby decoupling of local cycles is sufficient for the cycles to proceed out of phase, remains an important area of experimental research. The experiment reported here provides some first clues and may form a standard for forthcoming experiments to assess the mechanisms promoting asynchrony, persistence and possibly also stability.     

Diel and annual oxygen regimes in a small lake

An extensive ecosystem analysis program was conducted at the “Barlosche Kolk”, a small eutrophic lake in the eastern Netherlands, from September 1971 to September 1973. As part of this program, the oxygen concentration at different depths was determined continuously over several 24 hour periods. Although no well defined thermocline was observed, a marked oxygen stratification persisted during summer. Detailed pictures of the diel oxygen regime were constructed, showing strong dynamics especially during early autumn. Diel column-mean ranges were highly correlated with time of the year and diel patterns showed to be highly predictable.     

Immunological similarities between specific chloroplast ribosomal proteins from Chlamydomonas reinhardtii and ribosomal proteins from Escherichia coli

Polyclonal antibodies were elicited against seven of the 33 different proteins of the large subunit of the chloroplast ribosome from Chlamydomonas reinhardtii. Three of these proteins are synthesized in the chloroplast and four are made in the cytoplasm and imported. In western blots, six of the seven antisera are monospecific for their respective large subunit ribosomal proteins, and none of these antisera cross-reacted with any chloroplast small subunit proteins from C. reinhardtii. Antisera to the three chloroplast-synthesized ribosomal proteins cross-reacted with specific Escherichia coli large subunit proteins of comparable charge and molecular weight. Only one of the four antisera to the chloroplast ribosomal proteins synthesized in the cytoplasm cross-reacted with an E. coli large subunit protein. None of the antisera cross-reacted with any E. coli small subunit proteins. On the assumption of a procaryotic, endosymbiotic origin for the chloroplast, those chloroplast ribosomal proteins still synthesized within the organelle appear to have retained more antigenic sites in common with E. coli ribosomal proteins than have those which are now the products of cytoplasmic protein synthesis. Antisera to this cytoplasmically synthesized group of chloroplast ribosomal proteins did not recognize any antigenic sites among C. reinhardtii cytoplasmic ribosomal proteins, suggesting that the genes for the cytoplasmically synthesized chloroplast ribosomal proteins either are not derived from the cytoplasmic ribosomal protein genes or have evolved to a point where no antigenic similarities remain.      

Combinatorial delivery of small interfering RNAs reduces RNAi efficacy by selective incorporation into RISC

Despite the great potential of RNAi, ectopic expression of shRNA or siRNAs holds the inherent risk of competition for critical RNAi components, thus altering the regulatory functions of some cellular microRNAs. In addition, specific siRNA sequences can potentially hinder incorporation of other siRNAs when used in a combinatorial approach. We show that both synthetic siRNAs and expressed shRNAs compete against each other and with the endogenous microRNAs for transport and for incorporation into the RNA induced silencing complex (RISC). The same siRNA sequences do not display competition when expressed from a microRNA backbone. We also show that TAR RNA binding protein (TRBP) is one of the sensors for selection and incorporation of the guide sequence of interfering RNAs. These findings reveal that combinatorial siRNA approaches can be problematic and have important implications for the methodology of expression and use of therapeutic interfering RNAs.     

IGF-1 modulates gene expression of proteins involved in inflammation,cytoskeleton, and liver architecture

Even though the liver synthesizes most of circulating IGF-1, it lacks its receptor under physiological conditions. However, according to previous studies, a damaged liver expresses the receptor. For this reason, herein, we examine hepatic histology and expression of genes encoding proteins of the cytoskeleton, extracellular matrix, and cell-cell molecules and inflammation-related proteins. A partial IGF-1 deficiency murine model was used to investigate IGF-1’s effects on liver by comparing wild-type controls, heterozygous igf1^+/?, and heterozygous mice treated with IGF-1 for 10 days. Histology, microarray for mRNA gene expression, RT-qPCR, and lipid peroxidation were assessed. Microarray analyses revealed significant underexpression of igf1 in heterozygous mice compared to control mice, restoring normal liver expression after treatment, which then normalized its circulating levels. IGF-1 receptor mRNA was overexpressed in Hz mice liver, while treated mice displayed a similar expression to that of the controls. Heterozygous mice showed overexpression of several genes encoding proteins related to inflammatory and acute-phase proteins and underexpression or overexpression of genes which coded for extracellular matrix, cytoskeleton, and cell junction components. Histology revealed an altered hepatic architecture. In addition, liver oxidative damage was found increased in the heterozygous group. The mere IGF-1 partial deficiency is associated with relevant alterations of the hepatic architecture and expression of genes involved in cytoskeleton, hepatocyte polarity, cell junctions, and extracellular matrix proteins. Moreover, it induces hepatic expression of the IGF-1 receptor and elevated acute-phase and inflammation mediators, which all resulted in liver oxidative damage.     

Comparative cytotoxicity of fumonisin B1 in two cell lines derived from normal human bronchial epithelial cells using four distinct bioassay techniques

This study focuses on the cytotoxic effects of fumonisin B₁ (FB₁) on both immortalised and immortalised and subsequently transfected normal human bronchial epithelial (NHBE) cells of human origin using four bioassays. While the MTT, Neutral Red and hexosaminidase colorimetric assays showed little difference between the toxic effects on the two related cell lines, the clonogenic assay, measuring cell survival and proliferation, indicated that FB₁ had a more toxic effect on the nontransfected cells. This kind ofin vitro approach using cells which retain many characteristics of normal cell growth and differentiation can go some way to developing evaluation models for food safety in the case of mycotoxin contamination without resorting totally to whole animal testing. Nevertheless, one or two cytotoxicity tests may be inadequate for a complete appraisal of toxic potential: rather, as wide a range of methodologies as feasible should be employed initially before meaningful conclusions may be drawn.     

An acridinium sulphonylamide as a new chemiluminescent label for the determination of carboxylic acids in liquid chromatography

The synthesis of a new acridinium sulphonylamide label for the liquid chromatographic determination of carboxylic acids is described. The label 10-methyl-N-(p-tolyl)-N-(p-iodoacetamidobenzenesulphonyl)-9-acridinium carboxamide iodide is synthesized from 9-acridinecarboxylic acid by a seven-step reaction. Ibuprofen, used as test compound, is coupled to the reactive iodoacetamide group of the label by means of an alkylation reaction in dry acetonitrile for 20 min at 50°C in the presence of 18-crown-6 and potassium carbonate as base catalyst. The reaction mixture is injected into a liquid chromatographic system with chemiluminescence detection. Separation is performed on a Zorbax C₁₈ column with acetonitrile-water-tetrahydrofuran (39:57:4, v/v/v) containing 10 mmol/L TBABr and 0.035% H₂O₂ as the mobile phase at a flow rate of 1.0 ml/min. Chemiluminescence detection is achieved by the post-column addition of 200 mmol/L potassium hydroxide dissolved in methanol–water (1:1, v/v) at a flow rate of 20 μL/min. The detection limit (S/N = 3) of derivatized ibuprofen is 60 pg (3 pg injected). © 1998 John Wiley & Sons, Ltd.     

Differential Orientation of 10T1/2 Mesenchymal Cells on Non-Uniform Stretch Environments

Non-uniform stress and strain fields are prevalent in many tissues in vivo, and often exacerbated by disease or injury. These mechanical gradients potentially play a role in contributing to pathological conditions, presenting a need for experimental tools to allow investigation of cell behavior within non-uniformly stimulated environments. Herein, we employ two in vitro cell-stretching devices (one previously published; one newly presented) capable of subjecting cells to cyclic, non-uniform stretches upon the surface of either a circular elastomeric membrane or a cylindrical PDMS tube. After 24 hours of cyclic stretch, 10T1/2 cells on both devices showed marked changes in long-axis orientation, with tendencies to align parallel to the direction of minimal deformation. The degree of this response varied depending on location within the stretch gradients. These results demonstrated the feasibility of conducting cell mechanobiology investigations with the two novel devices, while also highlighting the experimental capabilities of non-uniform mechanical environments for these types of studies. Such capabilities include robust data collection for developing mechanobiological dose-response curves, signal threshold identification, and potential spatial targeting for drug delivery.     

Yield and quality of forage maize (<i>Zea mays</i> L.) with different levels of subsurface drip irrigation and plant density

The scarcity of water in arid and semiarid regions of the world is a problem that every day increases by climate change. The subsurface drip irrigation (SDI) and changes in population density of plants are alternatives that can be used to make a sustainable use of water. Therefore, the objectives of this study were to determine the combination that allows for an increased corn performance and efficient use of water without losing the quality of forage. Three different irrigation levels were applied through a system of a SDI at three different densities of forage maize plants in an arid region. The results demonstrated that by applying different levels of water, either enough or lack of soil moisture is created, which is directly reflected in crop yield, and its determining variables such as green forage and dry matter yield, and nutritional quality. The irrigation level to a 100% of potential evapotranspiration (PET), at a density of 80000 plants/ha, increased yield of green forage to 57664 kg/ha; crude protein was 8.59%, while the rest of the quality parameters decreased. This study allowed to conclude that the irrigation level was the major factor in the response of the crop.