Nascent Astrocyte Particles Differ from Lipoproteins in CSF

Abstract: Little is known about lipid transport and metabolism in the brain. As a further step toward understanding the origin and function of CNS lipoproteins, we have characterized by size and density fractionation lipoprotein particles from human CSF and primary cultures of rat astrocytes. The fractions were analyzed for esterified and free cholesterol, triglyceride, phospholipid, albumin, and apolipoproteins (apo) E, AI, AII, and J. As determined by lipid and apolipoprotein profiles, gel electrophoresis, and electron microscopy, nascent astrocyte particles contain little core lipid, are primarily discoidal in shape, and contain apoE and apoJ. In contrast, CSF lipoproteins are the size and density of plasma high-density lipoprotein, contain the core lipid, esterified cholesterol, and are spherical. CSF lipoproteins were heterogeneous in apolipoprotein content with apoE, the most abundant apolipoprotein, localized to the largest particles, apoAI and apoAII localized to progressively smaller particles, and apoJ distributed relatively evenly across particle size. There was substantial loss of protein from both CSF and astrocyte particles after density centrifugation compared with gel-filtration chromatography. The differences between lipoproteins secreted by astrocytes and present in CSF suggest that in addition to delivery of their constituents to cells, lipoprotein particles secreted within the brain by astrocytes may have the potential to participate in cholesterol clearance, developing a core of esterified cholesterol before reaching the CSF. Study of the functional properties of both astrocyte-secreted and CSF lipoproteins isolated by techniques that preserve native particle structure may also provide insight into the function of apoE in the pathophysiology of specific neurological diseases such as Alzheimer's disease.     

Beta diversity of a Gulf of California rocky-shore fish community

Synopsis Reef fish community composition in three segments of a peninsular rocky shoreline in the Gulf of California was estimated over four periods by visual observation. ‘Point’ and ‘bay’ segments had regular and distinct species compositions over most periods while a ‘middle’ segment was least distinct but consistently had the greatest number of species. Compositional change along the peninsula was least regular during the coldest sea temperature period (April). Mean species turnover between segments was highest between point and bay. Within segments, the point had greater compositional predictable composition (lowest species turnover). When species with regular frequency of encounter were classified into ‘point’, ‘middle’, ‘bay’, and ‘no trend’ groups it was found that comparatively more ‘point’ species had pelagic eggs and comparatively more ‘bay’ species had demersal eggs. Beta diversity of rocky-shore fishes along the physical gradient of the Punta Doble peninsula reflects a transition between exposed and protected rocky shoreline communities. The correlated physical environmental characteristics associated with exposed and protected habitats are discussed in relation to diversity regulation and dispersal strategies in reef fishes.     

Ecological disturbance influences adaptive divergence despite high gene flow in golden perch (Macquaria ambigua): Implications for management and resilience to climate change

Populations that are adaptively divergent but maintain high gene flow may have greater resilience to environmental change as gene flow allows the spread of alleles that have already been tested elsewhere. In addition, populations naturally subjected to ecological disturbance may already hold resilience to future environmental change. Confirming this necessitates ecological genomic studies of high dispersal, generalist species. Here we perform one such study on golden perch (Macquaria ambigua) in the Murray‐Darling Basin (MDB), Australia, using a genome‐wide SNP data set. The MDB spans across arid to wet and temperate to subtropical environments, with low to high ecological disturbance in the form of low to high hydrological variability. We found high gene flow across the basin and three populations with low neutral differentiation. Genotype–environment association analyses detected adaptive divergence predominantly linked to an arid region with highly variable riverine flow, and candidate loci included functions related to fat storage, stress and molecular or tissue repair. The high connectivity of golden perch in the MDB will likely allow locally adaptive traits in its most arid and hydrologically variable environment to spread and be selected in localities that are predicted to become arid and hydrologically variable in future climates. High connectivity in golden perch is likely due to their generalist life history and efforts of fisheries management. Our study adds to growing evidence of adaptation in the face of gene flow and highlights the importance of considering ecological disturbance and adaptive divergence in biodiversity management.     

A "20K" form of growth hormone in the murine pituitary gland

Extracts of mouse and rat adenohypophyses have been analyzed for a low-molecular-weight variant of growth hormone (GH) known to occur in humans, the so-called "20K"-GH (mol wt = 20,000 vs 22,000 for traditional human GH). Pituitary proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunostained with an antiserum raised against murine GH. Reactive and unreactive bands in close vicinity of the major GH band were fingerprinted by a peptide-mapping technique that reveals only the tyrosine-containing peptides, but can be applied to fingerprint single protein bands within gels. We found a protein band 2000 mol wt smaller than the major murine GH in both mouse and rat pituitary glands whose fingerprint resembled that of major GH. The peptide-mapping results are consistent with the interpretation that the internal deletion of amino acid residues most likely is in the same region of the molecule as in the human 20K-GH. Unlike the human 20K-GH, however, the murine counterpart showed no cross-reactivity with an antiserum raised against 22K-GH in the test system used here.     

Differentiation of Clostridium difficile Toxin from Clostridium botulinum Toxin by the Mouse Lethality Test

The mouse lethality test is the most sensitive method for confirming the diagnosis of infant botulism. Both Clostridium difficile and Clostridium botulinum produce heat-labile toxins which are lethal for mice and can be found in the feces of infants. These two toxins can be distinguished from one another in this assay when both are present in the same fecal specimen because they appear to be immunologically distinct toxins.     

Studies on proinsulin and proglucagon biosynthesis and conversion at the subcellular level: I. Fractionation procedure and characterization of the subcellular fractions

Anglerfish islets were homogenized in 0.25 M sucrose and separated into seven separate subcellular fractions by differential and discontinuous density gradient centrifugation. The objective was to isolate microsomes and secretory granules in a highly purified state. The fractions were characterized by electron microscopy and chemical analyses. Each fraction was assayed for its content of protein, RNA, DNA, immunoreactive insulin (IRI), and immunoreactive glucagon (IRG). Ultrastructural examination showed that two of the seven subcellular fractions contain primarily mitochondria, and that two others consist almost exclusively of secretory granules. A fifth fraction contains rough and smooth microsomal vesicles. The remaining two fractions are the cell supernate and the nuclei and cell debris. The content of DNA and RNA in all fractions is consistent with the observed ultrastructure. More than 82 percent of the total cellular IRI and 89(percent) of the total cellular IRG are found in the fractions of secretory granules. The combined fractions of secretory granules and microsomes consistently yield >93 percent of the total IRG. These results indicate that the fractionation procedure employed yields fractions of microsomes and secretory granules that contain nearly all the immunoassayable insulin and glucagons found in whole islet tissue. These fractions are thus considered suitable for study of proinsulin and proglucagon biosynthesis and their metabolic conversion at the subcellular level.     

Studies on proinsulin and proglucagon biosynthesis and conversion at the subcellular level: II. Distribution of radioactive peptide hormones and hormone precursors in subcellular fractions after pulse and pulse- chase incubation of islet tissue

Anglerfish proinsulin and insulin were selectively labeled with [(14)C]isoleucine, while proglucagon, conversion intermediate(s), and glucagon were selectively labeled with[(3)H]tryptophan. After various periods of continuous or pulse-chase incubation, islet tissue was subjected to subcellular fractionation. Fraction extracts were analyzed by gel filtration for their content of precursor, conversion intermediate(s), and product peptides. Of the seven subcellular fractions prepared after each incubation, only the microsome and secretory granule fractions yielded significant amounts of labeled insulin-related and glucagon-related peptides. After short-pulse incubations, levels of both [(14)C]proinsulin and [(3)H]proglucagon (mol wt approximately 12,000) were highest in the microsome fraction. This fraction is therefore identified as the site of synthesis. With increasing duration of continuous incubation or during chase incubation in the absence of isotopes, proinsulin, proglucagon, and conversion intermediate(s) are transported to secretory granules. Conversion of proinsulin to insulin and proglucagon to a approximately 4,900 mol wt conversion intermediate and 3,500 mol wt glucagon occurs in the secretory granules. Converting activity also was observed in the microsome fraction. The recovery of most of the incorporated radioactivity in microsome and secretory granule fractions indicates that the newly synthesized islet peptides are relegated to a membrane-bound state soon after synthesis at the RER is completed. This finding supports the concept of intracisternal sequestration and intragranular maintenance of peptides synthesized for export from the cell of origin.     

Evaluating the Performance of Chemical Control in the Presence of Resistant Pathogens

Resistance to chemical control is a major impediment to combating many socially and economically important diseases. Theoretical and experimental studies have shown that reducing the intensity of treatment can slow, or even prevent, the invasion of resistance, yet reducing treatment levels also results in a net increase in disease severity. Clearly there is a need to identify control strategies that balance the conflicting aims of resistance management and disease suppression. Using a mathematical model for the dynamics of fungicide resistance in crop pathogens, we present a broadly applicable measure of the performance of chemical control in the presence of resistant pathogen strains. We illustrate how to optimise fungicide performance with respect to the intensity of treatment as a function of the duration of treatment and the fitness of the resistant strain. We find that in the short term, fungicide performance is optimised at high levels of treatment despite rapid selection for resistance, while the long-term optimum performance is achieved when treatment renders the fungicide-sensitive and fungicide-resistant pathogens equally fit. We further present evidence that under prescribed conditions, the ratio of dose size and frequency, and the fungicide mode of action, can have a significant effect on fungicide performance.     

Establishment of Peristenus digoneutis and P. relictus (Hymenoptera: Braconidae) in California for the control of Lygus spp. (Heteroptera: Miridae)

Lygus hesperus Knight is native to the western United States and is a perennial pest of numerous crops in California. It is responsible for triggering the early season application of insecticides on cotton, Gossypium hirsutum L., and strawberries, Fragaria L. Despite several surveys conducted in alfalfa (Medicago sativa L.) grown in central California, nymphal parasitoids associated with L. hesperus and L. elisus have not been found. Two exotic parasitoids were released into California beginning in 1998. Peristenus relictus (Ruhte), formerly P. stygicus Loan, and P. digoneutis Loan were collected from several locations in southern Europe and released at up to six locations over a 6-year period. At the original release site in Sacramento, a 0.25-ha plot of alfalfa, parasitism by P. digoneutis and P. relictus combined increased from zero to 90%, 3 years after the last releases were made. Parasitoids have been recovered from vacant fields of weedy annuals within 2 km of this site. Recoveries at more southerly release sites in central California have been poor.     

蜘蛛丝蛋白的模块结构性能和重组表达

蜘蛛丝是一类天然蛋白质纤维,具有独特的机械性能（高强度、高弹性和高断裂功等）和卓著的生物学特性（生物可降解性和与生物组织的相容性等）,在生物医学、材料、纺织和军事等领域都有着很高的潜在应用价值。综述了不同蜘蛛丝蛋白的模块结构特征及与其功能的关系,扼要介绍了目前利用各种基因工程方法表达重组蜘蛛丝蛋白的研究进展。