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271.
Jean-Pierre Berry Marcel Chaintreau Danile Chassoux Robert Dennebouy Franoise Escaig Pierre Galle Jean-Michel Rossignol George Slodzian Sylvie Tlouzeau 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(1):65-72
Summary— The intra-cellular distribution of eight halogen glucocorticoids was investigated by ion microscopy in two cellular varieties of cultured non-cancer cells (fibroblast 3T3) and cancer cells (human breast tumor cells MCF-7). Two types of ion microscopy helped to determine this distribution, a direct imaging ion microscope (SMI 300) with low spatial resolution, and a scanning ion microscope (IMS4F), featuring high resolution, serving to obtain maps representing the intra-cellular distribution of the fluorine elements and drugs present in these monolayer cultured cells. The fluorine images representative of the drugs containing fluorine showed that these drugs are essentially concentrated in the cell nuclei. In these nuclei, the distribution of these drugs is different from that of heterochromatin and of the nucleolus. 相似文献
272.
273.
Patrick Cordier Michel Mendès France Philippe Bolon Jean Pailhous 《Acta biotheoretica》1994,42(2-3):187-201
Our work is aimed at studying the optimization of a complex motor behaviour from a global perspective. First, free climbing as a sport will be briefly introduced while emphasizing in particular its psychomotor aspect called route finding. The basic question raised here is how does the optimization of a sensorimotoricity-environment system take place. The material under study is the free climber's trajectory, viewed as the signature of climbing behaviour (i.e., the spatial dimension). The concepts of learning, optimization, constraint, and degrees of freedom of a system will be discussed using the synergistic approach to the study of movement (Bernstein, 1967; Kelso, 1977). Measures of a trajectory's length and convex hull can be used to define an index whose equation resembles that of an entropy. This index is a measure of the trajectory's overall complexity. Some important concepts related to the thermodynamics of curves will also be discussed. The optimization process will be studied by examining the changes in entropy over time for a set of trajectories generated during the learning of a route (ten successive repetitions of the same climb). It will be shown that the entropy of the trajectories decreases as learning progresses, that each level of expertise has its own characteristic entropy curve, and that for the subjects tested, the mean entropy of skilled climbers is lower than that of average climbers. Basing our analysis on the concepts of degrees of freedom and constraint equations, an attempt is made to relate trajectory entropy to system entropy. Based on the postulate that trajectory entropy is equal to the difference in entropy between the unconstrained and constrained system, a model of motor optimization is proposed. This model is illustrated by an entropy graph reflecting a dynamic release process. In the light of our results, two opposing views will be examined: movement construction vs. movement emergence. 相似文献
274.
275.
Evolutionary constraints on the ability of herbivores to efficiently use a set of phytochemically similar hosts, while maintaining
a high performance on phytochemically different hosts, are central in explaining the predominance of host specialization in
phytophagous insects. Such feeding trade-offs could be manifested within insect populations as negative genetic correlations
in fitness on different host species. We tested the hypothesis that feeding trade-offs were present within a population of
the obliquebanded leafroller,Choristoneura rosaceana (Harris). Components of fitness were measured in families originating from an apple orchard that were fed on four host-plant
species in the laboratory. Under the conditions of this experiment, all across-host genetic correlations were strongly positive,
suggesting that this population comprised true generalists. With the exception of diapausing propensity, the heritability
of the fitness components tended to be lower in caterpillars fed on apple leaves than in insects fed other hosts. This suggests
a constraint on the selective response of the fitness components in the orchard environment. 相似文献
276.
Murielle Rinaldi-Carmona Francis Barth Michel Haulme David Shire Bernard Calandra Christian Congy Serge Martinez Jeanne Maruani Gervais Nliat Daniel Caput Pascual Ferrara Philippe Soubri Jean Claude Brelire Grard Le Fur 《FEBS letters》1994,350(2-3):240-244
SR141716A is the first selective and orally active antagonist of the brain cannabinoid receptor. This compound displays nanomolar affinity for the central cannabinoid receptor but is not active on the peripheral cannabinoid receptor. In vitro, SR141716A antagonises the inhibitory effects of cannabinoid receptor agonists on both mouse vas deferens contractions and adenylyl cyclase activity in rat brain membranes. After intraperitoneal or oral administration SR141716A antagonises classical pharmacological and behavioural effects of cannabinoid receptor agonists. This compound should prove to be a powerful tool for investigating the in vivo functions of the anandamide/cannabinoid system. 相似文献
277.
The invasion kinetics ofhobo transposable element in theDrosophila melanogaster genome was studied byin situ hybridization on the polytene chromosomes. Six independent lines ofDrosophila melanogaster flies that had been previously transformed by microinjection of the pHFL1 plasmid containing a completehobo element were followed over 50 generations. We observed thathobo elements were scattered on each of the chromosome arms, with more insertion sites on the 3R arm. The total number of insertion sites remains quite small, between four and six, at generation 52. On the 2R arm, a short inversion appeared once at generation 52. Most of the integration sites reported here were already described for several transposons but some of them appear to be hotspots forhobo elements. 相似文献
278.
Núria Saperas Juan Ausio Domènec Lloris Manel Chiva 《Journal of molecular evolution》1994,39(3):282-295
Fish protamines are highly specialized molecules which are responsible for chromatin condensation during the last stages of spermatogenesis (spermiogenesis). However, not all fish contain protamines in their sperm nuclei; rather, there seems to be a random distribution of protamines within this group. The origin of this sporadic presence of protamines in the sperm and its significance have not yet been precisely determined. In this paper we have conducted an exhaustive survey of the literature available on the different types of nuclear protein composition of the sperm of teleost fish in order to try to correlate these data with what is presently known about the taxonomy of this group. The results of this analysis have allowed us to make the following observations. The divergence between protamines and histones has occurred several times during the evolution of the bony fish. However, the relative frequency of this divergence is almost negligible during the differentiation of genera and species (intrafamily variation) and is very small during the differentiation of families (interfamily variation). Nevertheless, the divergence is very noticeable among the different orders. It is therefore possible to conclude from all this that the sporadic distribution of protamines in bony fish is not a random event as initially believed. Furthermore, such a heterogeneous distribution of protamines cannot be easily accounted for by a mechanism of horizontal retroviral transmission through repeated and independent acquisition of a prot amine gene as has been recently proposed (Jankowski, Stater, Dixon (1986) J Mol Evol 23:1–10). Rather, it could possibly be explained by a repeated and independent loss of the expression of the protamine gene (or loss of the gene itself) which mainly occurred during the diversification of the orders of this group.Correspondence to: J. Ausio 相似文献
279.
R. Buès J. Freuler J. F. Toubon Susanna Gerber S. Poitout 《Entomologia Experimentalis et Applicata》1994,73(2):187-191
Homogeneous population structure in a migrant Lepidoptera, Agrotis ipsilon. Light trapping of Agrotis ipsilon (Lepidoptera, Noctuidae) on various passes of the Alps and Pyrénées exhibited wide range movements between overwintering and aestivation areas. Electrophoretic analysis of samples taken in the Cantons of Vaud and Tessin (Switzerland), in the Rhône Delta (Southern France), and on passes of the Alps and Pyrénées, showed a great temporal and spatial homogeneity of allele frequencies (Fst values ranging from 0.002 to 0.013, and genetic distances from 0 to 0.004). These results support the hypothesis of a high level of gene flow. However, the occurrence during some years of high Fis values, might be explained by mixtures of populations that had undergone selection or went through a bottle-neck. 相似文献
280.
F. Eber A. M. Chèvre A. Baranger P. Vallée X. Tanguy M. Renard 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(3-4):362-368
Spontaneous interspecific hybrids were produced under natural conditions (pollination by wind and bees) between a male-sterile cybrid Brassica napus (AACC, 2n = 38) and two weeds Brassica adpressa (AdAd, 2n = 14) and Raphanus raphanistrum (RrRr, 2n = 18). After characterization by chromosome counts and isozyme analyses, we observed 512 and 3 734 inter-specific seeds per m2 for the B. napus-B. adpressa and B. napus-R. raphanistrum trials respectively. Most of the hybrids studied had the expected triploid structure (ACX). In order to quantify the frequency of allosyndesis between the genomes involved in the hybrids, their meiotic behavior was compared to a haploid of B. napus (AC). For the B. napus-B. adpressa hybrids, we concluded that probably no allosyndesis occurred between the two parental genomes, and that genetic factors regulating homoeologous chromosome pairing were carried by the B. adpressa genome. For the B. napus-R. raphanistrum hybrids, high chromosome pairing and the presence of multivalents (in 9.16% of the pollen mother cells) indicate that recombination is possible between chromosomes of different genomes. Pollen fertility of the hybrids ranged from 0 to 30%. Blackleg inoculation tests were performed on the three parental species and on the interspecific hybrids. BC1 production with the weeds and with rapeseed was attempted. Results are discussed in regard to the risk assessment of transgenic rapeseed cultivation, F1 hybrid rapeseed variety production, and rapeseed improvement. 相似文献