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171.
A mutation in apolipoprotein A-I in the Iowa type of familial amyloidotic polyneuropathy 总被引:15,自引:0,他引:15
Immunoblotting of isoelectric focusing gels of plasma and direct genomic DNA sequencing have been used to characterize a mutation in apolipoprotein A-I associated with the familial amyloidotic polyneuropathy originally described by Van Allen in an Iowa kindred. An arginine for glycine substitution in apolipoprotein A-I identified in the proband's amyloid fibrils was determined to be the result of a mutation of guanine to cytosine in the apolipoprotein A-I gene at the position corresponding to the first base of codon 26. Direct sequencing of genomic DNA of three affected individuals who died in the 1960s confirmed the inheritance of the disorder. Immunoblot analysis detected the variant apolipoprotein A-I in the proband's plasma and in several at-risk members of the kindred. In addition, allele-specific amplification by the polymerase chain reaction was used to detect carriers of the variant gene. 相似文献
172.
Summary The ability of myogenic cells to migrate perpendicular to the long axis of freely autografted muscles was examined. Rat extensor digitorum longus muscles were divided, and one half was devitalized by repeated freezing in liquid nitrogen while the other half was kept viable in physiologic saline. The halves were reunited with sutures and grafted back into the original muscle bed. At intervals between 5 and 25 days the grafts were removed and examined histologically for the presence of myotubes within the devitalized region. Myotubes were first seen in the devitalized half 10 days postgrafting with the maximum number of myotubes observed after 12 to 15 days. These results indicate that myogenic cells are capable of migration perpendicular to the long axis of the muscle fibers in an autograft. 相似文献
173.
174.
Kyllinga nervosa (Steud.) and Sporobolus kentrophyllus (K. Schum.) are co-dominant plants of the Serengeti short-grass plains, Tanzania. The plains are characterized by seasonal and sporadic rainfall and currently support in excess of 1.5 million migratory ungulates. The interactive effect of simulated bovine urine and water availability were tested on the competitive interactions of these species in the laboratory.
Sporobolus kentrophyllus was a superior competitor to K. nervosa over the tested treatment levels with respect to growth and reproductive effort. Sporobolus kentrophyllus exhibited rapid growth in response to urine addition, leading to a significant species × urine interaction while reduced growth by K. nervosa in response to low water availability explained the significant species × water interaction and is likely explained by K. nervosa's shallow root system. Kyllinga nervosa, however, appears to be more tolerant of low nitrogen conditions based on its similar growth with and without the urine treatment. The effect of intraspecific competition on total biomass was similar for S. kentrophyllus and K. nervosa. Competition resulted in increased size differences (asymmetry) for K. nervosa and for the interspecific competition treatments compared to the size differences observed for plants grown individually (in absence of competition).Total reproductive biomass was reduced most by competition with S. kentrophyllus, irrespective of target species. The water treatment did not influence reproduction while the urine treatment significantly increased reproductive biomass and interacted with target species, competitor species, and yielded a three-way urine × target × competitor species interaction.Results suggest that codominance of these two species in the Serengeti is regulated by water availability, nitrogen input from grazers, and local neighbor identity. 相似文献
175.
176.
Jason J. Head Gregg F. Gunnell Patricia A. Holroyd J. Howard Hutchison Russell L. Ciochon 《Proceedings. Biological sciences / The Royal Society》2013,280(1763)
Mammals dominate modern terrestrial herbivore ecosystems, whereas extant herbivorous reptiles are limited in diversity and body size. The evolution of reptile herbivory and its relationship to mammalian diversification is poorly understood with respect to climate and the roles of predation pressure and competition for food resources. Here, we describe a giant fossil acrodontan lizard recovered with a diverse mammal assemblage from the late middle Eocene Pondaung Formation of Myanmar, which provides a historical test of factors controlling body size in herbivorous squamates. We infer a predominately herbivorous feeding ecology for the new acrodontan based on dental anatomy, phylogenetic relationships and body size. Ranking body masses for Pondaung Formation vertebrates indicates that the lizard occupied a size niche among the larger herbivores and was larger than most carnivorous mammals. Paleotemperature estimates of Pondaung Formation environments based on the body size of the new lizard are approximately 2–5°C higher than modern. These results indicate that competitive exclusion and predation by mammals did not restrict body size evolution in these herbivorous squamates, and elevated temperatures relative to modern climates during the Paleogene greenhouse may have resulted in the evolution of gigantism through elevated poikilothermic metabolic rates and in response to increases in floral productivity. 相似文献
177.
Harold E. Gregg 《Arts Education Policy Review》2013,114(10):15-18
178.
R V Gregg 《Journal of morphology》1966,119(1):81-88
The distribution and morphology of the argentaffin cell population within the stomach of the albino rat has been investigated histologically. The argentaffin cell's situation is restricted to and evenly distributed over the antrum, lying usually in the basal third of the mucosa among mucous cells. A band of mucosa, less than a millimeter wide, containing argentaffin cells, extends from the antrum and encircles the stomach just caudal to the forestomach. The argentaffin cell population is found in less than three-tenths of the total stomach by weight, a point for consideration in serotonin assay. 相似文献
179.
I Gregg 《BMJ (Clinical research ed.)》1991,302(6792):1600-1601
180.
Richard P. Shefferson Tiiu Kull Michael J. Hutchings Marc‐André Selosse Hans Jacquemyn Kimberly M. Kellett Eric S. Menges Richard B. Primack Juha Tuomi Kirsi Alahuhta Sonja Hurskainen Helen M. Alexander Derek S. Anderson Rein Brys Emilia Brzosko Slavomir Dostálik Katharine Gregg Zdeněk Ipser Anne Jäkäläniemi Jana Jersáková W. Dean Kettle Melissa K. McCormick Ana Mendoza Michael T. Miller Asbjørn Moen Dag‐Inge Øien Ülle Püttsepp Mélanie Roy Nancy Sather Nina Sletvold Zuzana Štípková Kadri Tali Robert J. Warren II Dennis F. Whigham 《Ecology letters》2018,21(5):724-733
Vegetative dormancy, that is the temporary absence of aboveground growth for ≥ 1 year, is paradoxical, because plants cannot photosynthesise or flower during dormant periods. We test ecological and evolutionary hypotheses for its widespread persistence. We show that dormancy has evolved numerous times. Most species displaying dormancy exhibit life‐history costs of sprouting, and of dormancy. Short‐lived and mycoheterotrophic species have higher proportions of dormant plants than long‐lived species and species with other nutritional modes. Foliage loss is associated with higher future dormancy levels, suggesting that carbon limitation promotes dormancy. Maximum dormancy duration is shorter under higher precipitation and at higher latitudes, the latter suggesting an important role for competition or herbivory. Study length affects estimates of some demographic parameters. Our results identify life historical and environmental drivers of dormancy. We also highlight the evolutionary importance of the little understood costs of sprouting and growth, latitudinal stress gradients and mixed nutritional modes. 相似文献