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排序方式: 共有800条查询结果,搜索用时 46 毫秒
791.
Danica Zivkovic Robbert Créton Gideon Zwaan René Dohmen 《Development genes and evolution》1991,200(6):320-329
Summary InLymnaea stagnalis, mesoderm induction occurs at the 24-cell stage, when the apical tip of the macromere 3D establishes a close contact with a number of micromeres. Via its tip, the macromere 3D is supposed to receive an inductive signal from the micromeres, resulting in the determination of the mesodermal stem cell 4d at the next division. In view of the possibility that transcellular ionic currents might somehow be involved, either in the processes that bring about this particular configuration of blastomeres or in the induction process itself, we mapped the electric field around the embryo during the 24-cell stage, using a vibrating probe. We detected a reversal of the current direction as compared to the uncleaved egg, whilst the polarity of the field along the animal-vegetal axis was maintained. We also mapped the localization of Ca2+-stimulated AT-Pase, an enzyme that drives the Ca2+-efflux from the cell. We found that this enzyme is localized exclusively along the cytoplasmic face of the apical plasma membrane of macromere 3D, and that its presence is restricted to the period from 110 to 135 min after the fifth cleavage, when there is close contact between macormere 3D and the micromeres. Since the localization of the Ca2+-stimulated ATPase coincides both in time and space with the induction of the mesoderm-mother cell, we suggest that localized calcium fluxes may play a role in this induction process. 相似文献
792.
Gideon Letz 《The Western journal of medicine》1983,138(4):534-540
Polychlorinated biphenyls (PCB''s) have low acute toxicity but are of public health concern because of their persistence in the environment, the bioaccumulation in human and animal tissues, and their potential for chronic or delayed toxicity.Although many questions remain unanswered, it is clear that occupational exposure, at a minimum, can produce dermatologic effects and liver dysfunction. The long half-life of PCB''s and their presence in various human tissues leaves open the possibility of substantial chronic and delayed effects analogous to those seen in animals. PCB''s are potent inhibitors of reproductive function in both rodents and nonhuman primates and produce liver tumors in animal cancer bioassays. As potent inducers of hepatic enzyme systems, PCB''s may have additional unpredictable long-term health effects.These effects have only recently begun to be studied in a rigorous manner, and although the epidemiological evidence is neither complete nor entirely consistent, there can be no question of the necessity to keep human exposures to the lowest feasible levels. 相似文献
793.
Gideon F. Inbar 《Biological cybernetics》1972,11(3):142-147
In a previous paper (Inbar, 1972/III) a new adaptive model was proposed for muscular control. According to that scheme muscle spindles (MS) supply continuous information about the system dynamics. In the present study integral pulse frequency modulation (IPFM) is used to correlate MS afferent signals, recorded from frog sartorius muscle, to the same muscle dynamics, in order to establish the feasibility of the proposed MS role in the adaptive muscle model. 相似文献
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The isoelectrofocusing patterns of
-amino acid oxidase (LAO) from venom gland homogenates and of the secreted venom of Vipera palaestinae have been compared. The LAO isozyme profile of actively synthesizing gland spans over a wider range of pIs (4.8–6.0) and includes more variants as compared with the profile of the secreted venom. A basic shift of the isoelectrofocusing pattern of LAO obtained by treatment of the gland homogenate or the venom with neuraminidase indicates that sialic acid residues are responsible for the changes in the electronegativity of the isozymes. Analyses of subcellular fractions show that the microsomal fraction of the venom gland homogenate exhibits the highest multiplicity of molecular forms of LAO, whereas the fraction including the secretory granules has an isozyme profile similar to the venom. Double labelling experiments show that the newly synthesized LAO include isozymes which span over a wide range of pIs, whereas later on labelling of the more acidic isozymes is prominent. The results obtained may suggest that the sialic acid residues which are attached to LAO during its transport serve as “markers” for secretion. 相似文献
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799.
The Bacillus thuringiensis var. thuringiensis strain 3A produces a proteinaceous parasporal crystal toxic to larvae of a variety of lepidopteran pests including Spodoptera littoralis (Egyptian cotton leaf worm), Heliothis zeae, H. virescens and Boarmia selenaria. By cloning of individual plasmids of B. thuringiensis in Escherichia coli, we localized a gene coding for the delta-endotoxin on the B. thuringiensis plasmid of about 17 kb designated pTN4. Following partial digestion of the B. thuringiensis plasmid pTN4 and cloning into the E. coli pACYC184 plasmid three clones were isolated in which toxin production was detected. One of these hybrid plasmids pTNG43 carried a 1.7-kb insert that hybridized to the 14-kb BamHI DNA fragments of B. thuringiensis var. thuringiensis strains 3A and berliner 1715. This BamHI DNA fragment of strain berliner 1715 has been shown to contain the gene that codes for the toxic protein of the crystal (Klier et al., 1982). No homologous sequences have been found between pTNG33 and the DNA of B. thuringiensis var. entomocidus strain 24, which exhibited insecticidal activity against S. littoralis similar to that of strain 3A. 相似文献
800.
Boris van Leeuwen Paul Smeets Jeanne Bovet Gideon Nave Jonathan Stieglitz Andrew Whitehouse 《Proceedings. Biological sciences / The Royal Society》2020,287(1941)
Economic preferences may be shaped by exposure to sex hormones around birth. Prior studies of economic preferences and numerous other phenotypic characteristics use digit ratios (2D : 4D), a purported proxy for prenatal testosterone exposure, whose validity has recently been questioned. We use direct measures of neonatal sex hormones (testosterone and oestrogen), measured from umbilical cord blood (n = 200) to investigate their association with later-life economic preferences (risk preferences, competitiveness, time preferences and social preferences) in an Australian cohort (Raine Study Gen2). We find no significant associations between testosterone at birth and preferences, except for competitiveness, where the effect runs opposite to the expected direction. Point estimates are between 0.05–0.09 percentage points (pp) and 0.003–0.14 s.d. We similarly find no significant associations between 2D : 4D and preferences (n = 533, point estimates 0.003–0.02 pp and 0.001–0.06 s.d.). Our sample size allows detecting effects larger than 0.11 pp or 0.22 s.d. for testosterone at birth, and 0.07 pp or 0.14 s.d. for 2D : 4D (α = 0.05 and power = 0.90). Equivalence tests show that most effects are unlikely to be larger than these bounds. Our results suggest a reinterpretation of prior findings relating 2D : 4D to economic preferences, and highlight the importance of future large-sample studies that permit detection of small effects. 相似文献