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1.
For several species of lepidoptera, most of the approximately 350-bp
mitochondrial control-region sequences were determined. Six of these
species are in one genus, Jalmenus; are closely related; and are believed
to have undergone recent rapid speciation. Recent speciation was supported
by the observation of low interspecific sequence divergence. Thus, no
useful phylogeny could be constructed for the genus. Despite a surprising
conservation of control-region length, there was little conservation of
primary sequences either among the three lepidopteran genera or between
lepidoptera and Drosophila. Analysis of secondary structure indicated only
one possible feature in common--inferred stem loops with higher-than-random
folding energies-- although the positions of the structures in different
species were unrelated to regions of primary sequence similarity. We
suggest that the conserved, short length of control regions is related to
the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In
addition, determination of flanking sequences for one Jalmenus species
indicated (i) only weak support for the available model of insect 12S rRNA
structure and (ii) that tRNA translocation is a frequent event in the
evolution of insect mitochondrial genomes.
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2.
Dennis BH Eberhart RC Dulikravich GS Radons SW 《Journal of biomechanical engineering》2003,125(6):832-840
Rapid cooling of the brain in the first minutes following the onset of cerebral ischemia is a potentially attractive preservation method. This computer modeling study was undertaken to examine brain-cooling profiles in response to various external cooling methods and protocols, in order to guide the development of cooling devices suitable for deployment on emergency medical vehicles. The criterion of successful cooling is taken to be the attainment of a 33 degrees C average brain temperature within 30 min of treatment. The transient cooling of an anatomically correct realistic 3-D head and neck with realistically varying local tissue properties was numerically simulated using the finite-element method (FEM). The simulations performed in this study consider ice packs applied to head and neck as well as using a head-cooling helmet. However, it was found that neither of these cooling approaches satisfies the 33 degrees C temperature within 30 min. This central conclusion of insubstantial cooling is supported by the modest enhancements reported in experimental investigations of externally applied cooling. The key problem is overcoming the protective effect of warm blood perfusion, which reaches the brain via the uncooled carotid arterial supply and effectively blocks the external cooling wave from advancing to the core of the brain. The results show that substantial cooling could be achieved in conjunction with neck cooling if the blood speed in the carotid artery is reduced from normal by a factor of 10. The results suggest that additional cooling means should be explored, such as cooling of other pertinent parts of the human anatomy. 相似文献
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It is shown that hidden Markov models (HMMs) are a powerful tool in the analysis of multielectrode data. This is demonstrated for a 30-electrode measurement of neuronal spike activity in the monkey's visual cortex during the application of different visual stimuli. HMMs with optimized parameters code the information contained in the spatiotemporal discharge patterns as a probabilistic function of a Markov process and thus provide abstract dynamical models of the pattern-generating process. We compare HMMs obtained from vector-quantized data with models in which parametrized output processes such as multivariate Poisson or binomial distributions are assumed. In the latter cases the visual stimuli are recognized at rates of more than 90% from the neuronal spike patterns. An analysis of the models obtained reveals important aspects of the coding of information in the brain. For example, we identify relevant time scales and characterize the degree and nature of the spatiotemporal variations on these scales. 相似文献
5.
Loksum Wong Cameron J Weadick Claire Kuo Belinda SW Chang Vincent Tropepe 《BMC developmental biology》2010,10(1):100
Background
The Dmbx1 gene is important for the development of the midbrain and hindbrain, and mouse gene targeting experiments reveal that this gene is required for mediating postnatal and adult feeding behaviours. A single Dmbx1 gene exists in terrestrial vertebrate genomes, while teleost genomes have at least two paralogs. We compared the loss of function of the zebrafish dmbx1a and dmbx1b genes in order to gain insight into the molecular mechanism by which dmbx1 regulates neurogenesis, and to begin to understand why these duplicate genes have been retained in the zebrafish genome. 相似文献6.
Combined monte carlo and molecular dynamics simulation of fully hydrated dioleyl and palmitoyl-oleyl phosphatidylcholine lipid bilayers
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We have applied a new equilibration procedure for the atomic level simulation of a hydrated lipid bilayer to hydrated bilayers of dioleyl-phosphatidylcholine (DOPC) and palmitoyl-oleyl phosphatidylcholine (POPC). The procedure consists of alternating molecular dynamics trajectory calculations in a constant surface tension and temperature ensemble with configurational bias Monte Carlo moves to different regions of the configuration space of the bilayer in a constant volume and temperature ensemble. The procedure is applied to bilayers of 128 molecules of POPC with 4628 water molecules, and 128 molecules of DOPC with 4825 water molecules. Progress toward equilibration is almost three times as fast in central processing unit (CPU) time compared with a purely molecular dynamics (MD) simulation. Equilibration is complete, as judged by the lack of energy drift in 200-ps runs of continuous MD. After the equilibrium state was reached, as determined by agreement between the simulation volume per lipid molecule with experiment, continuous MD was run in an ensemble in which the lateral area was restrained to fluctuate about a mean value and a pressure of 1 atm applied normal to the bilayer surface. Three separate continuous MD runs, 200 ps in duration each, separated by 10,000 CBMC steps, were carried out for each system. Properties of the systems were calculated and averaged over the three separate runs. Results of the simulations are presented and compared with experimental data and with other recent simulations of POPC and DOPC. Analysis of the hydration environment in the headgroups supports a mechanism by which unsaturation contributes to reduced transition temperatures. In this view, the relatively horizontal orientation of the unsaturated bond increases the area per lipid, resulting in increased water penetration between the headgroups. As a result the headgroup-headgroup interactions are attenuated and shielded, and this contributes to the lowered transition temperature. 相似文献
7.
Mice lacking the poly(ADP-ribose) polymerase gene are resistant to pancreatic beta-cell destruction and diabetes development induced by streptozocin 总被引:15,自引:0,他引:15
Burkart V Wang ZQ Radons J Heller B Herceg Z Stingl L Wagner EF Kolb H 《Nature medicine》1999,5(3):314-319
Human type 1 diabetes results from the selective destruction of insulin-producing pancreatic beta cells during islet inflammation. Cytokines and reactive radicals released during this process contribute to beta-cell death. Here we show that mice with a disrupted gene coding for poly (ADP-ribose) polymerase (PARP-/- mice) are completely resistant to the development of diabetes induced by the beta-cell toxin streptozocin. The mice remained normoglycemic and maintained normal levels of total pancreatic insulin content and normal islet ultrastructure. Cultivated PARP-/- islet cells resisted streptozocin-induced lysis and maintained intracellular NAD+ levels. Our results identify NAD+ depletion caused by PARP activation as the dominant metabolic event in islet-cell destruction, and provide information for the development of strategies to prevent the progression or manifestation of the disease in individuals at risk of developing type 1 diabetes. 相似文献
8.
Brefeldin A prevents uncovering but not phosphorylation of the recognition marker in cathepsin D 总被引:1,自引:0,他引:1
Brefeldin A (BFA) has been shown to inhibit transiently the subcellular transport of cathepsin D (Oda & Nishimura (1989) Biochem. Biophys. Res. Commun. 163, 220-225). We studied the effect of this antibiotic on processing of the phosphorylated oligosaccharides in cathepsin D in human promonocytes U937. In the presence of the drug the phosphorylation of cathepsin D precursor continued at a diminished rate. The phosphorylated oligosaccharides in cathepsin D comprised mono- and bis-phosphorylated forms. The relative amounts of the two species were not changed in the presence of BFA. The uncovering of the phosphate groups and the proteolytic processing of the phosphorylated precursor were abolished. In an in vitro assay the uncovering enzyme, N-acetylglucosamine-1-phosphodiester N-acetylglucosaminidase was not inhibited by BFA. We suggest that this drug interrupts the traffic between the compartments containing N-acetylglucosaminyl phosphotransferase and N-acetylglucosamine-1-phosphodiester N-acetylglucosaminidase. 相似文献
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