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971.
972.
Raman P Donkin SS Spurlock ME 《American journal of physiology. Regulatory, integrative and comparative physiology》2004,286(1):R206-R216
Direct effects of leptin on gluconeogenesis in rat hepatocytes are equivocal, and model systems from other species have not been extensively explored in assessing the regulation of glucose metabolism by leptin. Therefore, the goal of the present study was to compare the effects of leptin on gluconeogenesis in pig and rat hepatocyte cultures as well as to investigate an underlying mechanism of action at the level of phosphoenolpyruvate carboxykinase (PEPCK). In rat hepatocytes, leptin exposure (3 h, 50 and 100 nM) attenuated glucagon-stimulated hepatic gluconeogenesis by 35 and 38% (P < 0.05), respectively. However, leptin did not produce any significant acute effect in pig hepatocytes. Leptin exposure for 24 h failed to produce any significant effect on gluconeogenesis in either rat or pig hepatocytes cultured in the presence of glucagon or dexamethasone. Mechanistically, there was a 25-35% decrease (P < 0.05) in glucagon-induced PEPCK mRNA levels in rat but not pig hepatocytes cultured with leptin. This effect on PEPCK mRNA was not due to an alteration in the relative abundance of the leptin receptor or the ability of PEPCK to respond to cAMP. The nonuniformity of the effects of leptin on gluconeogenesis in pig and rat hepatocytes indicates differences in leptin action between species. Furthermore, the unique action of leptin in porcine hepatocytes points to the utility of this model system for biomedical research and also underscores the value of comparative studies. 相似文献
973.
Yoursy A. El-Kassaby Shawn Mansfield Fikret Isik Michael Stoehr 《Tree Genetics & Genomes》2011,7(3):553-561
The genetic control and phenotypic and genotypic correlations among wood density, modulus of elasticity, height, diameter,
and volume were assessed using 967 trees representing 20 unrelated 32-year-old coastal Douglas-fir full-sib families growing
on four (spaced and pruned vs. control) comparable test sites. Generally, no significant differences were observed between
treatments, indicating their limited effect at assessment time. Family effect did not differ for the growth traits; however,
significant differences were observed for wood density and both in situ methods (drilling resistance and acoustic velocity).
Growth and wood quality attributes, individually, produced high and positive phenotypic and genetic correlations; however,
high and negative correlations were observed between individual variables belonging to the two suites of attributes. Individual
tree heritabilities were low for growth (0.04 to 0.08) and modest to high for wood quality attributes (0.14 to 0.68). The
observed heritabilities and phenotypic and genotypic correlations imply modest to strong genetic control; however, they operated
in opposing direction. The significant and consistent genetic correlations between the in situ methods and wood density and
stiffness support their use as a non-destructive and economic assessment approach. The reliability of the in situ assessments
was verified through cumulative pith-to-bark wood density assessment, resulting in inconsistent genetic and phenotypic correlations
for early growth years. These latter findings imply that caution should be used in employing these in situ techniques as early
screening tools in breeding programs. 相似文献
974.
Alexandra E. Jantzen Whitney O. Lane Shawn M. Gage Justin M. Haseltine Lauren J. Galinat Ryan M. Jamiolkowski Fu-Hsiung Lin George A. Truskey Hardean E. Achneck 《Journal of visualized experiments : JoVE》2011,(55)
Implantable cardiovascular devices are manufactured from artificial materials (e.g. titanium (Ti), expanded polytetrafluoroethylene), which pose the risk of thromboemboli formation1,2,3. We have developed a method to line the inside surface of Ti tubes with autologous blood-derived human or porcine endothelial progenitor cells (EPCs)4. By implanting Ti tubes containing a confluent layer of porcine EPCs in the inferior vena cava (IVC) of pigs, we tested the improved biocompatibility of the cell-seeded surface in the prothrombotic environment of a large animal model and compared it to unmodified bare metal surfaces5,6,7 (Figure 1). This method can be used to endothelialize devices within minutes of implantation and test their antithrombotic function in vivo. Peripheral blood was obtained from 50 kg Yorkshire swine and its mononuclear cell fraction cultured to isolate EPCs4,8. Ti tubes (9.4 mm ID) were pre-cut into three 4.5 cm longitudinal sections and reassembled with heat-shrink tubing. A seeding device was built, which allows for slow rotation of the Ti tubes. We performed a laparotomy on the pigs and externalized the intestine and urinary bladder. Sharp and blunt dissection was used to skeletonize the IVC from its bifurcation distal to the right renal artery proximal. The Ti tubes were then filled with fluorescently-labeled autologous EPC suspension and rotated at 10 RPH x 30 min to achieve uniform cell-coating9. After administration of 100 USP/ kg heparin, both ends of the IVC and a lumbar vein were clamped. A 4 cm veinotomy was performed and the device inserted and filled with phosphate-buffered saline. As the veinotomy was closed with a 4-0 Prolene running suture, one clamp was removed to de-air the IVC. At the end of the procedure, the fascia was approximated with 0-PDS (polydioxanone suture), the subcutaneous space closed with 2-0 Vicryl and the skin stapled closed.After 3 - 21 days, pigs were euthanized, the device explanted en-block and fixed. The Ti tubes were disassembled and the inner surfaces imaged with a fluorescent microscope.We found that the bare metal Ti tubes fully occluded whereas the EPC-seeded tubes remained patent. Further, we were able to demonstrate a confluent layer of EPCs on the inside blood-contacting surface.Concluding, our technology can be used to endothelialize Ti tubes within minutes of implantation with autologous EPCs to prevent thrombosis of the device. Our surgical method allows for testing the improved biocompatibility of such modified devices with minimal blood loss and EPC-seeded surface disruption. 相似文献
975.
976.
Koichi Kamiya Yik Yuen Gan Shawn K. Y. Lum Min Sheng Khoo Siew Chin Chua Nik N. H. Faizu 《Tree Genetics & Genomes》2011,7(2):297-306
Shorea (Dipterocarpaceae) is a large genus in which many closely related species often grow together in Southeast Asian lowland
tropical rain forests. Many Shorea species share common pollinators, and earlier studies suggested occurrence of interspecific hybridization and introgression.
Here, we show morphological and molecular evidence of hybridization between Shorea species. In the census of all the trees of Shorea curtisii, Shorea leprosula, and Shorea parvifolia (>30 cm dbh) within the 164-ha area of Bukit Timah Nature Reserve in Singapore, we found 21 morphologically recognizable
hybrid individuals. All of the putative hybrids could be distinguished obviously from the parental species on the basis of
vegetative characters. Population genetic analysis of DNA sequences of two nuclear (GapC and PgiC) and chloroplast (trnL-trnF) regions demonstrated that each of the three species had several species-specific mutations. The nuclear sequences of the
putative hybrids were heterozygote at all the species-specific sites between two parental species. Hybrid between S. curtisii and S. leprosula was found most, while S. curtisii × S. parvifolia and S. leprosula × S. parvifolia hybrids were also found. Almost no shared polymorphism between populations of the parental species suggests rarity of introgression.
The study indicated that natural hybridization between sympatric Shorea species should not be uncommon, but all of the hybrid individuals were F1, and the post-F1 hybrids were considerably rare. 相似文献
977.
Xiao-Ming Sun Shawn B Bratton Michael Butterworth Marion MacFarlane Gerald M Cohen 《The Journal of biological chemistry》2002,277(13):11345-11351
Bcl-2 and Bcl-x(L) are reported to inhibit CD95-mediated apoptosis in "type II" but not in "type I" cells. In the present studies, we found that stimulation of CD95 receptors, with either agonistic antibody or CD95 ligand, resulted in the activation of caspase-8, which in turn processed caspase-3 between its large and small subunits. However, in contrast to control cells, those overexpressing either Bcl-2 or Bcl-x(L) displayed a distinctive pattern of caspase-3 processing. Indeed, the resulting p20/p12 caspase-3 was not active and did not undergo normal autocatalytic processing to form p17/p12 caspase-3, because it was bound to and inhibited by endogenous X-linked inhibitor-of-apoptosis protein (XIAP). Importantly, Bcl-2 and Bcl-x(L) inhibited the release of both cytochrome c and Smac from mitochondria. However, since Smac alone was sufficient to promote caspase-3 activity in vitro by inactivating XIAP, we proposed the existence of a death receptor-induced, Smac-dependent and apoptosome-independent pathway. This type II pathway was subsequently reconstituted in vitro using purified recombinant proteins at endogenous concentrations. Thus, mitochondria and associated Bcl-2 and Bcl-x(L) proteins may play a functional role in death receptor-induced apoptosis by modulating the release of Smac. Our data strongly suggest that the relative ratios of XIAP (and other inhibitor-of-apoptosis proteins) to active caspase-3 and Smac may dictate, in part, whether a cell exhibits a type I or type II phenotype. 相似文献
978.
Aim We introduce a method to quantify shared breaks in aggregate biotic distributions and their relationships to geographic variables. The method is based on quantification of distributional taxic and abiotic data that can be applied over multiple spatial scales. We aim to show biogeographic breaks and varying transition zones at a fine level of detail (5‐km resolution) and develop an approach to assess existing bioregionalization schemes. Location Global applicability, using an example from New South Wales in south‐eastern Australia. Methods Moving window analyses, rotated in 15° increments through 360°, are used to assess the degree of anisotropic spatial turnover between sets of gridded cells containing georeferenced species observations. Patterns of biotic turnover are compared with equivalent analyses for elevation and lithology. Identified breaks are assessed against an existing bioregionalization scheme (Interim Biogeographic Regionalisation of Australia, IBRA). Results There was fine‐scale concordance between turnover patterns and several IBRA bioregions. Breaks in turnover of flora and fauna corresponded with the boundaries of the Hunter Valley and Sydney Basin regions, particularly the boundary between the Brigalow Belt South and Sydney Basin. Low‐turnover zones were quantified; prominent examples are the Sydney Cataract and Wyong bioregions. Turnover along many boundaries was gradational, confirming that mapped breaks are not abrupt. A previously unidentified break was identified in the South East Corner bioregion. Spatial turnover patterns were similar between biota and were reflected in mean correlation coefficients between turnover in each group: mammals–reptiles (r = 0.70, P << 0.01); mammals–flora (r = 0.56, P << 0.01); and reptiles–flora (r = 0.51, P << 0.01). Generally, patterns of abiotic turnover reflected biotic turnover, although mean turnover correlations were weaker than between biota. Main conclusions Using this method we were able to characterize taxic breaks and overlaps in detail and at a spatially fine resolution. For our study region, we confirm the overall integrity of the IBRA framework, but suggest that it may benefit from revision in some respects. 相似文献
979.
Shane P. Mahoney Keith P. Lewis Jackie N. Weir Shawn F. Morrison J. Glenn Luther James A. Schaefer Darren Pouliot Rasim Latifovic 《Population Ecology》2016,58(1):91-103
The rates and causes of juvenile mortality are central features of the dynamics and conservation of large mammals, like woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)), but intrinsic and extrinsic factors may be modified by variations in animal abundance. We tested the influences of population size, climate, calf weight and sex on survival to 6 months of age of 1241 radio-collared caribou calves over three decades, spanning periods of population growth (1979–1997) and decline (2003–2012) in Newfoundland, Canada. Daily survival rates were higher and rose more quickly with calf age during the population growth period compared to the decline. Population size (negatively) and calf weight (positively) affected survival during the decline but neither had a detectable influence during the growth phase. Sex, climate and plant productivity (the latter two derived from the North Atlantic Oscillation and Normalized Difference Vegetation Index, respectively) exerted minimal influence during either phase. Predation was the dominant source of mortality. The mean percentage of calves killed by predators was 30 % higher during the decline compared to the growth phase. Black bears (Ursus americanus) and lynx (Lynx canadensis) were the major predators during the population increase but this changed during the decrease to black bears and coyotes (Canis latrans). Our findings are consistent with the hypothesis that Newfoundland caribou experienced phase-dependent survival mediated proximally by predation and competition for food. 相似文献
980.