Physical model for membrane protrusions during spreading

During cell spreading onto a substrate, the kinetics of the contact area is an observable quantity. This paper is concerned with a physical approach to modeling this process in the case of ameboid motility where the membrane detaches itself from the underlying cytoskeleton at the leading edge. The physical model we propose is based on previous reports which highlight that membrane tension regulates cell spreading. Using a phenomenological feedback loop to mimic stress-dependent biochemistry, we show that the actin polymerization rate can be coupled to the stress which builds up at the margin of the contact area between the cell and the substrate. In the limit of small variation of membrane tension, we show that the actin polymerization rate can be written in a closed form. Our analysis defines characteristic lengths which depend on elastic properties of the membrane-cytoskeleton complex, such as the membrane-cytoskeleton interaction, and on molecular parameters, the rate of actin polymerization. We discuss our model in the case of axi-symmetric and non-axi-symmetric spreading and we compute the characteristic time scales as a function of fundamental elastic constants such as the strength of membrane-cytoskeleton adherence.     

Proteomics based on peptide fractionation by SDS-free PAGE

Here we demonstrate the usefulness of peptide fractionation by SDS-free polyacrylamide gel electrophoresis and its applicability to proteomics studies. In the absence of SDS, the driving force for the electrophoretic migration toward the anode is supplied by negatively charged acidic amino acid residues and other residues as phosphate, sulfate and sialic acid, while the resulting mobility depends on both the charge and the molecular mass of the peptides. A straightforward method was achieved for SDS-PAGE of proteins, enzyme digestion, peptide transfer and fractionation by SDS-free PAGE, which was named dual-fractionation polyacrylamide gel electrophoresis (DF-PAGE). This method increases the number of identified proteins 2.5-fold with respect to the proteins identified after direct analysis, and more than 80% of assigned peptides were found in unique SDS-free gel slices. A vast majority of identified peptides (93%) have p I values below 7.0, and 7% have p I values between 7.0 and 7.35. Peptide digests that were derived from complex protein mixtures were in consequence simplified as peptides that are positively charged are not recovered in the present conditions. The analysis of a membrane protein extract from Neisseria meningitidis by this approach allowed the identification of 97 proteins, including low-abundance components.     

Extensive Rearrangements in the Chloroplast Genome of <Emphasis Type="Italic">Trachelium caeruleum</Emphasis> Are Associated with Repeats and tRNA Genes

Chloroplast genome organization, gene order, and content are highly conserved among land plants. We sequenced the chloroplast genome of Trachelium caeruleum L. (Campanulaceae), a member of an angiosperm family known for highly rearranged genomes. The total genome size is 162,321 bp, with an inverted repeat (IR) of 27,273 bp, large single-copy (LSC) region of 100,114 bp, and small single-copy (SSC) region of 7,661 bp. The genome encodes 112 different genes, with 17 duplicated in the IR, a tRNA gene (trnI-cau) duplicated once in the LSC region, and a protein-coding gene (psbJ) with two duplicate copies, for a total of 132 putatively intact genes. ndhK may be a pseudogene with internal stop codons, and clpP, ycf1, and ycf2 are so highly diverged that they also may be pseudogenes. ycf15, rpl23, infA, and accD are truncated and likely nonfunctional. The most conspicuous feature of the Trachelium genome is the presence of 18 internally unrearranged blocks of genes inverted or relocated within the genome relative to the ancestral gene order of angiosperm chloroplast genomes. Recombination between repeats or tRNA genes has been suggested as a mechanism of chloroplast genome rearrangements. The Trachelium chloroplast genome shares with Pelargonium and Jasminum both a higher number of repeats and larger repeated sequences in comparison to eight other angiosperm chloroplast genomes, and these are concentrated near rearrangement endpoints. Genes for tRNAs occur at many but not all inversion endpoints, so some combination of repeats and tRNA genes may have mediated these rearrangements.     

黄瓜子叶节离体培养物花分化Ca2+敏感期的研究

植物开花是一个非常复杂的过程,对其机理的研究有着重要的实践意义和理论意义。近百年来进行了广泛的生理生化研究,提出过多种假设。自90年代初成功分离了花器官分化和发育基因以来,使这一研究领域进入了分子水平。钙不仅是植物的矿质营养元素之一,而且Ca~(2+)作为植物的第二信使,参与细胞内多种生理生化活动。许多研究结果表明,Ca~(2+)在成花诱导、花芽形成和分化过程中起重要作用,我们自建立黄瓜子叶培养物离     

黄瓜子叶节离体培养物花分化Ca^2＋敏感期的研究（简报）

Cotyledonary nodes of cucumber cultured on calcium-free medium for 0, 1, 2, 3, 4, 5, 6d respectively, were transferred to medium with 6.0 mmol/L CaCl2 for 24h, then returned to calcium-free medium. Cotyledonary nodes cultured on calcium-free or 6.0 mmol/L CaCl2 medium for all time, were taken as controls. Results showed that cotyledonary nodes were transferred to 6.0 mmol/L CaCl2 medium for 24h during 0-3d after the beginning of culture, percentage of floral bud formation at cotyledonary nodes was increased significantly. Transferring cotyledonary nodes on the 3d day after the beginning of culture was achieved best effect, percentage of floral bud formation was up to 34.3%. We deduced that the calcium sensitive period during floral differentiation of cucumber cotyleddonary node cultured in vitro may be 0-4d after the beginning of culture.     

Host plant density and patch isolation drive occupancy and abundance at a butterfly's northern range margin

Marginal populations are usually small, fragmented, and vulnerable to extinction, which makes them particularly interesting from a conservation point of view. They are also the starting point of range shifts that result from climate change, through a process involving colonization of newly suitable sites at the cool margin of species distributions. Hence, understanding the processes that drive demography and distribution at high‐latitude populations is essential to forecast the response of species to global changes. We investigated the relative importance of solar irradiance (as a proxy for microclimate), habitat quality, and connectivity on occupancy, abundance, and population stability at the northern range margin of the Oberthür's grizzled skipper butterfly Pyrgus armoricanus. For this purpose, butterfly abundance was surveyed in a habitat network consisting of 50 habitat patches over 12 years. We found that occupancy and abundance (average and variability) were mostly influenced by the density of host plants and the spatial isolation of patches, while solar irradiance and grazing frequency had only an effect on patch occupancy. Knowing that the distribution of host plants extends further north, we hypothesize that the actual variable limiting the northern distribution of P. armoricanus might be its dispersal capacity that prevents it from reaching more northern habitat patches. The persistence of this metapopulation in the face of global changes will thus be fundamentally linked to the maintenance of an efficient network of habitats.     

Phenylbutyrate up-regulates the adrenoleukodystrophy-related gene as a nonclassical peroxisome proliferator

X-linked adrenoleukodystrophy (X-ALD) is a demyelinating disease due to mutations in the ABCD1 (ALD) gene, encoding a peroxisomal ATP-binding cassette transporter (ALDP). Overexpression of adrenoleukodystrophy-related protein, an ALDP homologue encoded by the ABCD2 (adrenoleukodystrophy-related) gene, can compensate for ALDP deficiency. 4-Phenylbutyrate (PBA) has been shown to induce both ABCD2 expression and peroxisome proliferation in human fibroblasts. We show that peroxisome proliferation with unusual shapes and clusters occurred in liver of PBA-treated rodents in a PPARalpha-independent way. PBA activated Abcd2 in cultured glial cells, making PBA a candidate drug for therapy of X-ALD. The Abcd2 induction observed was partially PPARalpha independent in hepatocytes and totally independent in fibroblasts. We demonstrate that a GC box and a CCAAT box of the Abcd2 promoter are the key elements of the PBA-dependent Abcd2 induction, histone deacetylase (HDAC)1 being recruited by the GC box. Thus, PBA is a nonclassical peroxisome proliferator inducing pleiotropic effects, including effects at the peroxisomal level mainly through HDAC inhibition.     

Shear flow-induced detachment kinetics of Dictyostelium discoideum cells from solid substrate

Using Dictyostelium discoideum as a model organism of specific and nonspecific adhesion, we studied the kinetics of shear flow-induced cell detachment. For a given cell, detachment occurs for values of the applied hydrodynamic stress above a threshold. Cells are removed from the substrate with an apparent first-order rate constant that strongly depends on the applied stress. The threshold stress depends on cell size and physicochemical properties of the substrate, but is not affected by depolymerization of the actin and tubulin cytoskeleton. In contrast, the kinetics of cell detachment is almost independent of cell size, but is strongly affected by a modification of the substrate and the presence of an intact actin cytoskeleton. These results are interpreted in the framework of a peeling model. The threshold stress and the cell-detachment rate measure the local equilibrium energy and the dissociation rate constant of the adhesion bridges, respectively.