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排序方式: 共有119条查询结果,搜索用时 31 毫秒
31.
The purpose of this study was to investigate medfly longevity and reproduction across a broad spectrum of diet restriction using a protocol similar to those applied in most rodent studies. Age-specific reproduction and age of death were monitored for 1200 adult males and 1200 females, each individually maintained on one of 12 diets from ad libitum to 30% of ad libitum. Diet was provided in a fixed volume of solution that was fully consumed each day, ensuring control of total nutrient consumption for every fly. Contrary to expectation and precedence, increased longevity was not observed at any level of diet restriction. Among females, reproduction continued across all diet levels despite the cost in terms of increased mortality. Among males, life expectancy exceeded that of females at most diet levels. However, in both sexes, mortality increased more sharply and the pattern of survival changed abruptly once the diet level fell to 50% of ad libitum or below, even though the energetic demands of egg production has no obvious counterpart in males. We believe that a more complete picture of the life table response to dietary restriction will emerge when studies are conducted on a wider range of species and include both sexes, more levels of diet, and the opportunity for mating and reproduction. 相似文献
32.
Lawrence G. Harshman Andrew G. Clark 《Evolution; international journal of organic evolution》1998,52(5):1334-1341
In field studies of multiple mating and sperm competition there typically is no experimental control over the number of times that a female mates, the interval between matings, or the genetic identity of multiple fathers contributing to a brood. Irrespective of this complexity, high-resolution molecular markers can be used to assign paternity with considerable confidence. This study employed two highly heterozygous microsatellite loci to assess multiple paternity and sperm displacement in a sample of broods taken from a natural population of Drosophila melanogaster. The large number of alleles present at each of the loci makes it difficult to derive explicit maximum-likelihood estimates for multiple paternity and sperm displacement from brood samples. Monte Carlo simulations were used to estimate maximum-likelihood parameters for the distribution of female remating frequency and the proportion of offspring sired by the second or subsequent mating males. Estimates were made based on genotypes scored at two distinct marker loci because they were found to give statistically homogeneous results. Fitting a Poisson distribution of number of matings, the mean number of males mated by a female was 1.82. The sperm displacement parameter estimated from doubly mated females were 0.79 and 0.86 for the two loci (0.83 for the joint estimate). The overall probability that a multiply mated female will be misclassified as singly mated was only 0.006, which indicates that microsatellites can provide excellent resolution for identifying multiple mating. In addition, microsatellites can be used to generate relatively precise estimates of sperm precedence in brood-structured samples from a natural population. 相似文献
33.
S. Harshman J. G. Conlin D. Stoller D. L. Harshman 《The Journal of membrane biology》1979,50(2):177-185
Summary Isolated plasma membranes from mouse fibroblast lines 3T3 and its tranformant SV-3T3 contain a phosphodiesterase (oligonucleotidase, E.C. 3.1.4.19; nucleotide pyrophosphatase, E.C. 3.6.1.9) that splits capped and methylated messenger RNA obtained from both reovirus and vesicular stomatitis virus. The isolated membranes are free of demonstrable ribonuclease activity and split the mRNA to produce 7-methyl guanosine diphosphate as a product. With ATP as substrate for the phosphodiesterase enzyme, the product is AMP. Synthetic caps, AMP, ADP and ATP, but not cyclic AMP, can compete with the substratep-nitrophenyl thymidilic acid. A possible regulatory role on messenger translation is proposed. 相似文献
34.
Sidney Harshman 《Molecular and cellular biochemistry》1979,23(3):143-152
Summary Recent developments in the area of Staphylococcal -toxin studies are presented which modify the concepts previously held with respect to both biological and physical properties of -toxin. New data concerning the nature of the binding site for -toxin on rabbit erythrocyte membranes and a model to explain the various observed complexes of -toxin and membrane receptor are discussed. Finally, evidence suggesting that Staphylococcal -toxin is a potent demyelinating agent is presented.The work was supported in part by NSF grant PCM 77-19307 相似文献
35.
Epoxide hydrolase and glutathione S-transferase activities toward trans- and cis-stilbene oxides were measured in 3 strains of Drosophila melanogaster. Differences in age dependence, substrate selectivity and subcellular location were detected suggesting the presence of multiple forms of these enzymes. In addition, interstrain differences indicate the presence of genetic variation for epoxide hydrolase and glutathione transferase activities. These results illustrate a potential use of these assays in D. melanogaster to complement existing tests (e.g. recessive lethal tests or Ames assays) for evaluating the relationship between epoxide hydrolase and glutathione S-transferase levels and the genotoxicity of epoxides. 相似文献
36.
Sheila Unger Maria W. Górna Antony Le Béchec Sonia Do Vale-Pereira Maria Francesca Bedeschi Stefan Geiberger Giedre Grigelioniene Eva Horemuzova Faustina Lalatta Ekkehart Lausch Cinzia Magnani Sheela Nampoothiri Gen Nishimura Duccio Petrella Francisca Rojas-Ringeling Akari Utsunomiya Bernhard Zabel Sylvain Pradervand Keith Harshman Belinda Campos-Xavier Luisa Bonafé Giulio Superti-Furga Brian Stevenson Andrea Superti-Furga 《American journal of human genetics》2013
37.
Shchedrina VA Kabil H Vorbruggen G Lee BC Turanov AA Hirosawa-Takamori M Kim HY Harshman LG Hatfield DL Gladyshev VN 《The Journal of biological chemistry》2011,286(34):29449-29461
Selenoproteins are essential in vertebrates because of their crucial role in cellular redox homeostasis, but some invertebrates that lack selenoproteins have recently been identified. Genetic disruption of selenoprotein biosynthesis had no effect on lifespan and oxidative stress resistance of Drosophila melanogaster. In the current study, fruit flies with knock-out of the selenocysteine-specific elongation factor were metabolically labeled with (75)Se; they did not incorporate selenium into proteins and had the same lifespan on a chemically defined diet with or without selenium supplementation. These flies were, however, more susceptible to starvation than controls, and this effect could be ascribed to the function of selenoprotein K. We further expressed mouse methionine sulfoxide reductase B1 (MsrB1), a selenoenzyme that catalyzes the reduction of oxidized methionine residues and has protein repair function, in the whole body or the nervous system of fruit flies. This exogenous selenoprotein could only be expressed when the Drosophila selenocysteine insertion sequence element was used, whereas the corresponding mouse element did not support selenoprotein synthesis. Ectopic expression of MsrB1 in the nervous system led to an increase in the resistance against oxidative stress and starvation, but did not affect lifespan and reproduction, whereas ubiquitous MsrB1 expression had no effect. Dietary selenium did not influence lifespan of MsrB1-expressing flies. Thus, in contrast to vertebrates, fruit flies preserve only three selenoproteins, which are not essential and play a role only under certain stress conditions, thereby limiting the use of the micronutrient selenium by these organisms. 相似文献
38.
Ary A. Hoffmann Lawrence G. Harshman 《Evolution; international journal of organic evolution》1985,39(3):638-644
Effects of male Drosophila melanogaster on female fecundity and productivity were examined, considering both females held in containers with males and females exposed to male effects not involving contact. Females were more fecund when male effects were present, and the largest increase was recorded when vials were previously conditioned by males. This effect was probably due to the growth of transmitted microorganisms, which were observed on the laying surface, as further experiments with vials conditioned by virgin females showed a similar increase in fecundity. A male-specific effect was isolated by conditioning bottles containing only agar with males and virgin females. The observation of a male factor that stimulates oviposition without mating is novel and suggests complicated fertility interactions between the sexes. 相似文献
39.
The cost of reproduction is of fundamental importance in life-history evolution. However, our understanding of its mechanistic basis has been limited by a lack of detailed functional information at all biological levels. Here, we identify, evaluate and integrate recent studies in five areas examining the proximate mechanisms underlying the cost of reproduction. Rather than being alternate explanations, hormonal regulation and intermediary metabolism act in concert and have an overarching influence in shaping the cost of reproduction. Immune function is compromised by reproduction, as is resistance to environmental stress. These studies not only provide new information about mechanisms that comprise 'the cost', but also hint at an underlying evolutionarily conserved causal mechanism. 相似文献
40.
Bart Buitenhuis Luc LG Janss Nina A Poulsen Lotte B Larsen Mette K Larsen Peter S?rensen 《BMC genomics》2014,15(1)