岛屿生物地理学理论：模型与应用

前言岛屿有许多显著特征,如地理隔离,生物类群简单。这些特点为重复性研究和统计学分析奠定了基础,从而有利于许多深入而细致的生物学研究。因此,岛屿为发展和检验自然选择、物种形成及演化,以及生物地理学和生态学诸领域的理论和假设,提供了重要的自然实验室。岛屿生物地理学理论(MacArthurwilson学说)即为岛屿生物学研究中所产生的著名理论之一。该理论发展之     

Heat Shock RNA Levels in Brain and Other Tissues After Hyperthermia and Transient Ischemia

A number of studies have demonstrated increased synthesis of heat shock proteins in brain following hyperthermia or transient ischemia. In the present experiments we have characterized the time course of heat shock RNA induction in gerbil brain after ischemia, and in several mouse tissues after hyperthermia, using probes for RNAs of the 70-kilodalton heat shock protein (hsp70) family, as well as ubiquitin. A synthetic oligonucleotide selective for inducible hsp70 sequences proved to be the most sensitive indicator of the stress response whereas a related rat cDNA detected both induced RNAs and constitutively expressed sequences that were not strongly inducible in brain. Considerable polymorphism of ubiquitin sequences was evident in the outbred mouse and gerbil strains used in these studies when probed with a chicken ubiquitin cDNA. Brief hyperthermic exposure resulted in striking induction of hsp70 and several-fold increases in ubiquitin RNAs in mouse liver and kidney peaking 3 h after return to room temperature. The oligonucleotide selective for hsp70 showed equivalent induction in brain that was more rapid and transient than observed in liver, whereas minimal induction was seen with the ubiquitin and hsp70-related cDNA probes. Transient ischemia resulted in 5- to 10-fold increases in hsp70 sequences in gerbil brain which peaked at 6 h recirculation and remained above control levels at 24 h, whereas a modest 70% increase in ubiquitin sequences was noted at 6 h. These results demonstrate significant temporal and quantitative differences in heat shock RNA expression between brain and other tissues following hyperthermia in vivo, and indicate that hsp70 provides a more sensitive index of the stress response in brain than does ubiquitin after both hyperthermia and ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

70-Kilodalton Heat Shock Protein Induction in Cerebellar Astrocytes and Cerebellar Granule Cells In Vitro: Comparison with Immunocytochemical Localization After Hyperthermia In Vivo

Induction of the 70-kDa heat shock protein, hsp70, was evaluated in cultured cerebellar astrocytes and granule cell neurons subjected to a hyperthermic stress, using a monoclonal antibody and an oligonucleotide probe that selectively recognize stress-inducible species of hsp70-related proteins and RNAs, respectively. Immunoblots of cultures enriched in either granule cells or astrocytes, and immunocytochemical localization studies in cocultures of these cell types, demonstrated that hsp70 induction was restricted to the astrocyte population. Amino acid incorporation experiments showed little difference in the loss and recovery of overall protein synthesis activity in these two cell types following transient hyperthermic stress. RNA blot hybridizations confirmed the preferential glial induction of hsp70. In vivo immunocytochemical studies in brains of adult rats following hyperthermia were consistent with earlier observations that suggested a primarily glial and vascular localization of the heat shock response in most brain regions, although the intense immunoreactivity in the cerebellar granule cell layer suggests that there is induction of hsp70 in these neurons under in vivo conditions. These results suggest the potential value of such defined cell cultures in identifying mechanisms responsible for differences in the heat shock response of various cell types in vitro, and in revealing factors that may account for the apparent absence of the stress response in cultured cerebellar granule cell neurons.     

HSP12, a new small heat shock gene of Saccharomyces cerevisiae: Analysis of structure, regulation and function

Summary We have isolated a new small heat shock gene, HSP12, from Saccharomyces cerevisiae. It encodes a polypeptide of predicted Mr 12 kDa, with structural similarity to other small heat shock proteins. HSP12 gene expression is induced several hundred-fold by heat shock and on entry into stationary phase. HSP12 mRNA is undetectable during exponential growth in rich medium, but low levels are present when cells are grown in minimal medium. Analysis of HSP12 expression in mutants affected in cAMP-dependent protein phosphorylation suggests that the gene is regulated by cAMP as well as heat shock. A disruption of the HSP12 coding region results in the loss of an abundant 14.4 kDa protein present in heat shocked and stationary phase cells. It also leads to the induction of the heat shock response under conditions normally associated with low-level HSP12 expression. The HSP12 disruption has no observable effect on growth at various temperatures, nor on the ability to acquire thermotolerance.     

Roles of Escherichia coli heat shock proteins DnaK, DnaJ and GrpE in mini-F plasmid replication

Summary A subset of Escherichia coli heat shock proteins, DnaK, DnaJ and GrpE were shown to be required for replication of mini-F plasmid. Strains of E. coli K12 carrying a missense mutation or deletion in the dnaK, dnaJ, or grpE gene were virtually unable to be transformed by mini-F DNA at the temperature (30° C) that permits cell growth. When excess amounts of the replication initiator protein (repE gene product) of mini-F were provided by means of a multicopy plasmid carrying repE, these mutant bacteria became capable of supporting mini-F replication under the same conditions. However, the copy number of a high copy number mini-F plasmid was reduced in these mutant bacteria as compared with the wild type in the presence of excess RepE protein. Furthermore, mini-F plasmid mutants that produce altered initiator protein and exhibit a very high copy number were able to replicate in strains deficient in any of the above heat shock proteins. These results indicate that the subset of heat shock proteins (DnaK, DnaJ and GrpE) play essential roles that help the functioning of the RepE initiator protein in mini-F DNA replication.     

Effects of temperature on cytomorphogenesis and ultrastructure ofMicrasterias denticulata Bréb

Summary Exposure of growingMicrasterias cells to high (32°–36°C) and low (3°–10°C) temperatures produces changes in morphology that are accompanied by several ultrastructural alterations. Whereas low temperatures essentially cause simplification of cell ornamentation, a variety of cell malformations result from high temperature treatment. These are the loss of cell symmetry leading to markedly aberrant cell shapes and an increase of main lobes with reduced degree of differentiation. Preliminary studies indicate that a shift in the distribution of membrane-associated Ca²⁺ by elevated temperatures probably underlies these abnormal cytomorphogenetic events. Both, low and high temperature cause a reduction in size of the young half cell and affect cytoplasmic streaming. Moreover, nuclear migration is retarded and chloroplast arrangement is influenced by temperature treatment at both ranges. Growth velocity of primary wall responsible for cell shaping is increased at high and slowed down at low temperatures compared to cells grown at 20°C.The main ultrastructural alterations induced by high temperatures are an increase in amount and length of ER cisternae, the appearance of heat shock granule aggregations localized in the cytoplasm, a reduced number of ribosomes and polysomes, the presence of oil bodies in growing cells and a varying thickness of the primary wall. Influences of low temperatures on ultrastructure are less pronounced. They are manifested in the formation of large aggregations of ER cisternae slightly differing from those found in untreated cells, a disturbed arrangement of the microtubule system surrounding the nucleus and a decrease of the number of cell wall forming cytoplasmic vesicles.It is thought that most of the temperature effects are due to an influence on membranes probably an alteration of ionic currents and, in addition, a modulation of normal protein synthesis.Dedicated to my teacher Professor Oswald Kiermayer in deep gratitude     

Arabidopsis: Sensitivity of growth to high temperature

Arabidopsis thaliana seedlings as measured by an electrolyte leakage assay, have been found to be extremely sensitive to high temperature stress as compared to a high temperature tolerant variety (Tracy) of soybean. Over 50% ion leakage occurred in Arabidopsis leaves during a 15-minute exposure to 50°C, indicating a heat killing time of less than 15 minutes. In contrast, the heat killing time for soybean at 50°C was over five times longer. When soybean or Arabidopsis seedlings in culture plates were exposed to 37°C for 2 hours and then returned to 23°C, they suffered no apparent short-term or long-term damage. Soybean seedlings given a 42°C, treatment for 2 hours also showed no damage. Arabidopsis seedlings after a 42°C treatment for 2 hours showed no apparent immediate damage, but 48 hours after return to 23°C severe damage symptoms were visible and after 96 hours all the seedlings were dead. Both soybean and Arabidopsis seedlings synthesize heat shock proteins (hsps) when exposed to 42°C for 2 hours. The hsps synthesized are of similar molecular weights, although the relative abundances of the different size classes are very different in the two plants. Even though hsps are produced in Arabidopsis seedlings after a 2 hour exposure to 42°C their presence is not sufficient for the seedlings to recover from the effects of rhe heat shock when returned to 23°C. Our results show that Arabidopsis has a heat sensitive genotype. This along with its other characteristics should make it a good model system in which to assay in transgenic plants, the functions of homologous and heterologous genes that might be candidates for determining heat tolerance in plants.     

Resuscitation of Vibrio cholerae O1 strain TSI-4 from a viable but nonculturable state by heat shock

Abstract Vibrio cholerae strain TSI-4 was incubated in an M9 salt solution at 15 °C for more than 100 days. The plate counts showed no viable cells on day 30, but a broth culture from that day showed the growth of bacteria. However, after 35 days the bacteria entered the nonculturable state, based on the assessment of both the plate counts and broth culture. A portion of the culture was heated at 45 °C for 1 min in a water bath and subsequently plated onto a nutrient agar plate. More than 1000 colonies were recovered after this heat-shock treatment. The recovered cells showed the same chromosomal DNA pattern in the restriction map and the same outer membrane protein pattern in SDS-PAGE. Recovery of viable cells by heat-shock was achieved in cultures grown on M9 salt but not from cultures grown in phosphate-buffered saline. This suggests that the presence of NH₄Cl in the M9 salt solution may support the growth of the bacteria in a low nutrient medium, while also playing an important role in resuscitation.