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151.
Optical tweezers (infrared laser-based optical traps) have emerged as a powerful tool in molecular and cell biology. However, their usefulness has been limited, particularly in vivo, by the potential for damage to specimens resulting from the trapping laser. Relatively little is known about the origin of this phenomenon. Here we employed a wavelength-tunable optical trap in which the microscope objective transmission was fully characterized throughout the near infrared, in conjunction with a sensitive, rotating bacterial cell assay. Single cells of Escherichia coli were tethered to a glass coverslip by means of a single flagellum: such cells rotate at rates proportional to their transmembrane proton potential (. J. Mol. Biol. 138:541-561). Monitoring the rotation rates of cells subjected to laser illumination permits a rapid and quantitative measure of their metabolic state. Employing this assay, we characterized photodamage throughout the near-infrared region favored for optical trapping (790-1064 nm). The action spectrum for photodamage exhibits minima at 830 and 970 nm, and maxima at 870 and 930 nm. Damage was reduced to background levels under anaerobic conditions, implicating oxygen in the photodamage pathway. The intensity dependence for photodamage was linear, supporting a single-photon process. These findings may help guide the selection of lasers and experimental protocols best suited for optical trapping work. 相似文献
152.
The threonine sensitive aspartokinase-homoserine dehydrogenase devoid of aspartokinase activity has been extracted from a missense mutant of K12 and some of its properties have been investigated. The genetic localization of the corresponding mutation indicated that the amino acid replacement lies in the kinase region of the molecule. The cooperativity of threonine inhibition of the homoserine dehydrogenase activity is lowered. The measurement of the molecular weight of the enzyme in presence or absence of threonine indicates that the molecule dissociates more easily than the wild type enzyme. These results are discussed in view of the recent structural model proposed for aspartokinase I-homoserine dehydrogenase I. 相似文献
153.
J.E.N. Veron 《Journal of insect physiology》1973,19(8):1689-1703
The chromatophore-containing integument of Austrolestes annulosus always changes from a dark to a blue colour phase in vitro and therefore functions independently of a central control mechanism. In isolated abdominal segments, the reverse colour change occurs independently of the presence of central nervous system. The amount of change decreases with the size of the piece of integument; it varies over different parts of the body of the same intact insect, and it varies both in vitro and in vivo with time of day.A variety of experiments, involving ligation of abdominal segments and ablation of their ganglia, show that the terminal ganglion is primarily responsible for the release of a darkening factor which migrates in an anterior direction. Other ventral ganglia have a similar function but are of less importance.Transplants of terminal ganglia and injection of their extracts fail to restore capacity for colour change in ligature-isolated segments which have had their own ganglia removed. These findings, supported by histological observations, suggest that the darkening factor is a neurosecretion. 相似文献
154.
155.
156.
The F-spondin genes are a family of extracellular matrix molecules united
by two conserved domains, FS1 and FS2, at the amino terminus plus a
variable number of thrombospondin repeats at the carboxy terminus.
Currently, characterized members include a single gene in Drosophila and
multiple genes in vertebrates. The vertebrate genes are expressed in the
midline of the developing embryo, primarily in the floor plate of the
neural tube. To investigate the evolution of chordate F-spondin genes, I
have used the basal position in chordate phylogeny of the acraniate
amphioxus. A single F-spondin-related gene, named AmphiF-spondin, was
isolated from amphioxus. Based on molecular phylogenetics, AmphiF-spondin
is closely related to a particular subgroup of vertebrate F-spondin genes
that encode six thrombospondin repeats. However, unlike these genes,
expression of AmphiF-spondin is not confined to the midline but is found
through most of the central nervous system. Additionally, AmphiF-spondin
has lost three thrombospondin repeats and gained two fibronectin type III
repeats, one of which has strong identity to a fibronectin type III repeat
from Deleted in Colorectal Cancer (DCC). Taken together, these results
suggest a complex evolutionary history for chordate F-spondin genes that
includes (1) domain loss, (2) domain gain by tandem duplication and
divergence of existing domains, and (3) gain of heterologous domains by
exon shuffling.
相似文献
157.
M.-L. Patou J. Chen L. Cosson D. H. Andersen C. Cruaud A. Couloux E. Randi S. Zhang & G. Veron 《Journal of Zoology》2009,278(3):218-230
The masked palm civet is distributed through south-east Asia, China and the Himalayas. Because of its potential role in the severe acute respiratory syndrome (SARS) epidemic, it has become important to gather information on this species, and notably to provide a tool to determine the origin of farm and market animals. For this purpose, we studied the genetic variability and the phylogeographic pattern of the masked palm civet Paguma larvata . First, two portions of mitochondrial genes, cytochrome b and the control region, were sequenced for a total of 76 individuals sampled from China, the Indochinese region and the Sundaic region. Results indicated a low genetic variability and suggested a lack of a phylogeographic structure in this species, which do not allow inferring the geographic origin of samples of unknown origin, although it is possible to distinguish individuals from China and the Sundaic region. This low variation is in contrast to the well-marked morphological differentiation between the populations in the Sundaic and Chinese–Indochinese regions. We also used five microsatellite loci to genotype 149 samples from two wild and four farmed populations in China, where the masked palm civet is farmed and where the SARS coronavirus was isolated. These analyses also showed a reduced variability in Chinese civets and showed that farmed populations did not exhibit a lower genetic diversity than wild populations, suggesting frequent introductions of wild individuals into farms. 相似文献
158.
159.
Multigene phylogeny of the Mustelidae: Resolving relationships,tempo and biogeographic history of a mammalian adaptive radiation 总被引:1,自引:0,他引:1
Klaus-Peter Koepfli Kerry A Deere Graham J Slater Colleen Begg Keith Begg Lon Grassman Mauro Lucherini Geraldine Veron Robert K Wayne 《BMC biology》2008,6(1):10
Background
Adaptive radiation, the evolution of ecological and phenotypic diversity from a common ancestor, is a central concept in evolutionary biology and characterizes the evolutionary histories of many groups of organisms. One such group is the Mustelidae, the most species-rich family within the mammalian order Carnivora, encompassing 59 species classified into 22 genera. Extant mustelids display extensive ecomorphological diversity, with different lineages having evolved into an array of adaptive zones, from fossorial badgers to semi-aquatic otters. Mustelids are also widely distributed, with multiple genera found on different continents. As with other groups that have undergone adaptive radiation, resolving the phylogenetic history of mustelids presents a number of challenges because ecomorphological convergence may potentially confound morphologically based phylogenetic inferences, and because adaptive radiations often include one or more periods of rapid cladogenesis that require a large amount of data to resolve. 相似文献160.
BLA Verçosa CM Lemos IL Mendonça SMMS Silva SM de Carvalho H Goto FAL Costa 《BMC veterinary research》2008,4(1):45