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221.
Theodore Gurney Jr. Margaret J. Woolf Leslie J. Abplanalp Nichole H. McKittrick Jeanne N. Dietz Barry C. Cole 《In vitro cellular & developmental biology. Plant》1981,17(11):993-996
Summary Four monolayer mammalian cell lines were cured ofMycoplasma hyorhinis infections by cloning in microtiter dishes in the presence of tetracycline and kanamycin. During cloning, cultures were refed
with fresh antibiotic containing medium every 2 or 3 d for 14 d and were then cultured without effective antibiotics for at
least 21 d. From the four lines we recovered 29 clones, none of which were infected after treatment as judged by the lack
of extranuclear fluorescence after staining with the fluorochrome Hoechst 33258, and by normal autoradiographic labeling of
the cells by tritiated nucleosides. One clone from each line was tested further by attempted culture of mycoplasmas and was
also judged to be uninfected. Infection has not reappeared in any of the clones after extensive culture in the absence of
the effective antibiotics.
This investigation was supported by Public Health Service Research Grant GM26137 from the National Institutes of General Medical
Sciences, National Institutes of Health, Bethesda, MD. 相似文献
222.
Douglas Speirs Sarah Lawrie Dave Raffaelli William Gurney Chas Emes 《Journal of experimental marine biology and ecology》2002,280(1-2):13-31
We investigated factors potentially affecting tidal migrations over the littoral zone by invertebrate predators via a combination of strategic modelling, field observations and laboratory experiments using the mysid Neomysis integer. The models predict the distribution of individuals over the immersed intertidal region under the three different scenarios of diffusive movement, movement up a gradient of prey abundance, and movement towards a specific water depth. We reject the diffusive spread hypothesis since the predicted changes in spatial patterns are qualitatively inconsistent with those of density estimates over the tidal cycle in the field. The foraging hypothesis was consistent with the field samples only if there was a consistent upshore food gradient. Gut contents analysis showed meiofaunal prey were rare, but that organic detritus was the main dietary component. Sediment samples indicated some evidence of an organic matter gradient, but in the laboratory, Neomysis showed no preference for sediment with high organic content. We therefore rejected the foraging hypothesis. The depth-seeking model was not rejected, but laboratory experiments involving responses to various predators of Neomysis provided only weak evidence that depth-seeking was a result of predator avoidance. We hypothesise that the proximate mechanism is most likely to involve behavioural responses to flow conditions. 相似文献
223.
The aim of this paper is to reconcile the observed vulnerability of self-sustaining (materially closed) experimental ecosystems with demonstrations of virtually unconditional stability in mathematical models incorporating material recycling. We prove deterministic local stability in a generalized version of a model previously investigated by two of us (Nisbet and Gurney), but show that, except with rather narrowly specified parameter values, the system is likely to be extremely sensitive to external perturbations. 相似文献
224.
225.
Dwight E. Wilson David Woodard Abby Sandler Jill Erickson Austin Gurney 《Biochemical genetics》1987,25(1-2):1-6
The segregation of the mouse gene for uridine monophosphatase-2 (Umph-2) was examined in 14 independent mouse-Syrian hamster hybrids and 10 hybrid subclones. Umph-2 cosegregated with the mouse galactokinase (Glk) gene in 23 of the 24 hybrids and showed at least four discordances with all other mouse marker isozymes examined. The observed synteny of Umph-2 and Glk, which has also been observed in humans, indicates that the mouse Umph-2 gene is on chromosome 11. 相似文献
226.
A suite of models has been formulated to investigate the dynamic consequences of the various routes by which uniform larval competition for food can find demographic expression. It is found that while delayed expression through the vital rates of later age classes gives rise to limit cycles containing multiple overlapping generations, immediate expression via changes in the death or growth rates of the larvae themselves leads to self-sustaining single generation limit cycles. When immediate expression of competition is combined with high adult fecundity and short reproductive lifespan the amplitude of the single generation cycles is so large that they constitute a series of evenly spaced discrete generations, which is maintained indefinitely even in the absence of external cues. 相似文献
227.
Monoclonal antibodies against simian virus 40 tumor antigens: analysis of antigenic binding sites, using adenovirus type 2-simian virus 40 hybrid viruses. 总被引:16,自引:12,他引:4
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The antigenic binding sites of two monoclonal antibodies are located in the COOH-terminal region (clone 412) and probably in an internal region (clone 7) of simian virus 40 large T antigen. A third monoclonal antibody (clone 122), which has been shown to bind nonviral T antigen, does not react with HeLa cells infected with nondefective adenovirus type 2 (Ad2)-simian virus 40 hybrid viruses Ad2+ND1, Ad2+ND2, or Ad2+ND4. 相似文献
228.
The systematic formulation of population models for insects with dynamically varying instar duration
We develop a formalism for insect population dynamics which covers the situation where maturation from one instar to its successor is triggered by weight gain and not by chronological age. We specify assumptions which result in the instantaneous “subpopulations” of various instars obeying delay-defferential equations with time delays (representing instar duration) which are themselves dynamic variables, changing in response to the availability of food. We demonstrate the stabilizing potential of variable time delays by studying an idealised two-stage model in which maturation to the adult stage occurs after absorption of a given (fixed) quantity of food. 相似文献
229.
Young W. Kwon Susan J. Abbondanzo Colin L. Stewart Mark E. Gurney 《Developmental neurobiology》1995,28(1):35-50
We show that leukemia inhibitory factor (LIF) plays a physiological role in the programmed withdrawal of synapses form neonatal muscles. First, LIF mRNA is present in embryonic skeletal muscle and is developmentally regulated. We detect high levels of LIF mRNA at embryonic day 17 (E17) in mouse hind leg muscles. The content of LIF mRNA falls 10-fold between E17 and birth and then remains low in the neonate and adult. The decrease in LIF mRNA in skeletal muscle coincides with the end of secondary myogenesis and the completion of the adult number of myofibers. Second, treatment of the mouse tensor fascia latae (TFL), a superficial muscle of the hind leg, with LIF from birth (100 ng/day), transiently delays the withdrawal of excess inputs from polyneuronally innervated myofibers by approximately 3 days. The midpoint of the process is shifted from 7.5 ± 0.5 to 10.2 ± 0.6 days of age. LIF treatment delays synapse withdrawal by altering its timing without an appreciable effect on its rate. Third, in mice homozygous for a distruption of the LIF gene, the midpoint in the reduction of multiply innervated TFL myofibers occurs 1 day earlier, at 6.5 ± 0.5 days of age. Muscle fiber number is unchanged in LIF null mice. Treatment with LIF does not alter the rate of neonatal growth, the number of muscle fibers in the TFL, or the reappearance of inputs that have been eliminated. Instead, LIF appears to delay maturation of the motor unit by transiently delaying the onset of synapse withdrawal. We hypothesize that this is a necessary component of a selective process that will operate simultaneously and equally on multiple, competing motor units. © 1995 John Wiley & Sons, Inc. 相似文献