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11.
Raymond W. Bethke 《Oecologia》1993,93(1):102-108
Geographical gradients of persistence in community structure have been suggested to be causally related to underlying gradients of species diversity, environmental variability and/or productivity. In order to test whether the persistence of breeding duck communities was dependent on any one of these three factors, thirty-three years of census data from the Canadian prairie and boreal forest regions was examined along geographical gradients of wetland habitat variability and productivity. For breeding ducks, locally derived patterns of persistence were generally independent of local habitat conditions. Persistence appeared to be related more to patterns of emigration and immigration in response to climatic conditions (i.e., drought) in the southern prairies than to local species richness, wetland habitat variability or productivity. It is suggested, therefore, that analyses of community persistence derived at small spatial scales may be of limited value if the structure of communities is not regulated by local conditions. 相似文献
12.
P G Swift J R Hearnshaw J L Botha G Wright N T Raymond K F Jamieson 《BMJ (Clinical research ed.)》1993,307(6896):96
OBJECTIVES--To document the number of children aged less than 15 years who developed diabetes and were managed within one large health district, and to evaluate the outcome of those children managed without hospital admission at diagnosis. DESIGN--A retrospective study over 1979-88, when a paediatrician and a physician with special interests in childhood diabetes initiated joint clinics. Data collected from the district diabetes register and files of consultants and health visitors specialising in diabetes. SETTING--Referral of children to consultants in Leicestershire (total population 863,000). MAIN OUTCOME MEASURES--The proportion of children managed without hospital admission, comparison of readmission rates and glycated haemoglobin concentrations between children admitted and those not admitted. RESULTS--Over 10 years 236 children aged 10-14 years developed diabetes (annual incidence rate 12.8/100,000 child population (95% confidence interval 11.3 to 14.7)). In total 138 were not admitted to hospital but received supervised management based at home. Admitted children were younger or acidotic or their family doctors did not contact the diabetes team. Duration of admission declined from seven days in 1979-80 to three days in 1987-8. Ninety two were not admitted to hospital during the 10 years for any reason. Significantly fewer children who received management at home were readmitted for reasons related to diabetes than the group treated in hospital (30 (22%) v 40 (41%); p = 0.004). Concentrations of glycated haemoglobin were no different between the two groups. CONCLUSIONS--Children with newly diagnosed diabetes may be safely and effectively managed out of hospital. Domiciliary or community based management depends on the commitment of consultants specialising in diabetes working in close cooperation with general practitioners, specialist nurses in diabetes, and dietitians. 相似文献
13.
J. L. V. Broers Barbie M. Machiels Helma J. H. Kuijpers Frank Smedts Ronald van den Kieboom Yves Raymond Frans C. S. Ramaekers 《Histochemistry and cell biology》1997,107(6):505-517
A selection of normal human tissues was investigated for the presence of lamins B1, B2, and A-type lamins, using a panel
of antibodies specific for the individual lamin subtypes. By use of immunoprecipitation and two-dimensional immunoblotting
techniques we demonstrated that these antibodies do not cross-react with other lamin subtypes and that a range of different
phosphorylation isoforms is recognized by each antibody. The lamin B2 antibodies appeared to decorate the nuclear lamina in
all tissues examined, except hepatocytes, in which very little lamin B2 expression was observed. In contrast to previous studies,
which suggested the ubiquitous expression of lamin B1 in mammalian tissues, we show that lamin B1 is not as universally distributed
throughout normal human tissues as was to be expected from previous studies. Muscle and connective tissues are negative, while
in epithelial cells lamin B1 seemed to be preferentially detected in proliferating cells. These results correspond well with
those obtained for lamin B1 in chicken tissues. The expression of A-type lamins is most prominent in well-differentiated epithelial
cells. Relatively undifferentiated and proliferating cells in epithelia showed a clearly reduced expression of A-type lamins.
Furthermore, most cells of neuroendocrine origin as well as most hematopoietic cells were negative for A-type lamin antibodies.
Accepted: 4 February 1997 相似文献
14.
Corinna Richter Ron L. Dy Rebecca E. McKenzie Bridget N.J. Watson Corinda Taylor James T. Chang Matthew B. McNeil Raymond H.J. Staals Peter C. Fineran 《Nucleic acids research》2014,42(13):8516-8526
Clustered regularly interspaced short palindromic repeats (CRISPR), in combination with CRISPR associated (cas) genes, constitute CRISPR-Cas bacterial adaptive immune systems. To generate immunity, these systems acquire short sequences of nucleic acids from foreign invaders and incorporate these into their CRISPR arrays as spacers. This adaptation process is the least characterized step in CRISPR-Cas immunity. Here, we used Pectobacterium atrosepticum to investigate adaptation in Type I-F CRISPR-Cas systems. Pre-existing spacers that matched plasmids stimulated hyperactive primed acquisition and resulted in the incorporation of up to nine new spacers across all three native CRISPR arrays. Endogenous expression of the cas genes was sufficient, yet required, for priming. The new spacers inhibited conjugation and transformation, and interference was enhanced with increasing numbers of new spacers. We analyzed ∼350 new spacers acquired in priming events and identified a 5′-protospacer-GG-3′ protospacer adjacent motif. In contrast to priming in Type I-E systems, new spacers matched either plasmid strand and a biased distribution, including clustering near the primed protospacer, suggested a bi-directional translocation model for the Cas1:Cas2–3 adaptation machinery. Taken together these results indicate priming adaptation occurs in different CRISPR-Cas systems, that it can be highly active in wild-type strains and that the underlying mechanisms vary. 相似文献
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18.
Ludo Filez Willy Stalmans Freddy Penninkx Raymond Kerremans Karel Geboes 《Bioscience reports》1987,7(12):917-923
Lactate dehydrogenase has been measured in the small-intestinal mucosa in order to assess its value as a marker for the effects of ischemia and of reperfusion. The decrease in specific activity of the enzyme illustrates the deleterious effect of reperfusion on the quality of the remaining epithelial cells. However, this parameter fails to detect the loss of epithelial cells, which is the major event during ischemia as well as during reperfusion. In contrast, the expression of enzyme activity per g protein of the underlying intestinal muscle allowed us, in addition, to assess quantitatively the loss of epithelial cells, in good agreement with the histological data. 相似文献
19.
Roy E. Weber Frank B. Jensen Raymond P. Cox 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(2):145-152
Summary The allosteric effects of the erythrocytic nucleoside triphosphates (NTP) and of proton concentrations were investigated by precise measurement of Hb–O2 equilibria of tench hemoglobin (including extreme, high and low saturation ranges) and analysed in terms of the MWC two state model and the Adair four step oxygenation theory.At low concentrations (NTP/Hb ratio=1.0, and pH>7.3) ATP, GTP and protons decrease Hb–O2 affinity by increasing the allosteric constantL and reducingK
T, the association constant1 of the deoxy, tense state of the Hb, without significantly affecting that (K
R) of the oxy state, increasing the free energy of cooperativity (G). High concentrations of these effectors, however, also reduceK
R. The greater sensitivity of the half-saturation O2 tension (P
50) of the Hb to GTP than to ATP at the same concentration, correlates with greater effects of GTP on bothK
T andK
R. The pH and NTP dependence of the four Adair association constants and the calculated fractional populations of Hb molecules in different stages of oxygenation show that the autochthonous NTP effectors and protons stabilize the T structure and postpone the TR transition basic to cooperativity in fish Hb.The possible implications of the findings for aquatic respiration are discussed.Abbreviations
ATP
adenosine triphosphate
-
DPG
2,3-diphosphoglycerate (glycerate-2,3-bisphosphate)
-
GTP
guanosine triphosphate
-
IHP
inositol hexaphosphate
-
NTP
nucleoside triphosphates
In this paperK
T andK
R are defined as theassociation equilibrium constants instead of dissociation constants (as originally defined by Monod et al. 1965) to facilitate comparison with the Adair constants 相似文献
20.
Strains of Culex pipiens derived from natural populations collected in southern France were crossed to determine their ability to give fertile offspring. Uni- and bi-directional incompatibilities occurred between these strains and each of them had its own crossing properties. Compatibility or incompatibility of a cross seemed to be related to the geographic distance separating the parental colonies, but not to their ecological origin (hypogeous or epigeous). Our results showed evidence for the variation in time of crossing properties of a strain. 相似文献