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1.
Wikan A 《Journal of mathematical biology》2001,43(6):471-500
Discrete age-structured density-dependent one-population models and discrete age-structured density-dependent prey–predator
models are considered. Regarding the former, we present formal proofs of the nature of bifurcations involved as well as presenting
some new results about the dynamics in unstable and chaotic parameter regions. Regarding the latter, we show that increased
predation may act both as a stabilizing and a destabilizing effect. Moreover, we find that possible periodic dynamics of low
period, either exact or approximate, may not be generated by the predator, but it may be generated by the prey. Finally, what
is most interesting from the biological point of view, is that given that the prey, in absence of the predator, exhibits periodic
or almost periodic oscillations of low period, then the introduction of the predator does not alter this periodicity in any
substantial way until the stabilizing effect of increased predation becomes so strong that a stable equilibrium is achieved.
Received: 16 June 2000 / Revised version: 18 January 2001 / Published online: 12 October 2001 相似文献
2.
Some forms of testicular germ cell tumors (TGCTs) arise from primordial germ cells (PGCs) during fetal development. In both
humans and mice, genetic control of susceptibility is complex, involving both Mendelian and polygenic factors. Identification
and characterization of TGCT genes will provide insight not only into the basis for inherited susceptibility, but also into
the genetic control of the development of the PGC lineage. Recent work has revealed the identity of several susceptibility
genes that are inherited as Mendelian traits, the chromosomal location of yet-to-be identified TGCT susceptibility genes,
as well as clues to the nature of developmental pathways involved in tumorigenesis. In this review we summarize current understanding
of the biology and genetics of TGCTs in mice and discuss the relevance of this work to testicular cancer in humans.
Received: 18 September 2000 / Accepted: 4 October 2000 相似文献
3.
Avian colour vision and avian video playback experiments 总被引:2,自引:0,他引:2
I. C. Cuthill N. S. Hart J. C. Partridge A. T. D. Bennett S. Hunt S. C. Church 《Acta ethologica》2000,3(1):29-37
Video playback potentially allows the presentation, manipulation, and replication of realistic moving visual stimuli, in a
way that is impossible with real animals or static dummies, and difficult even with mechanical models. However, there are
special problems attached to the use of this technology; this article concentrates on the problem of accurate colour rendition.
Video and television simulate the colour of objects rather than reproduce the spectrum of light that they naturally emit,
transmit, or reflect. This simulation is achieved by using relatively narrow waveband light to stimulate the cone cells in
the retina in a similar pattern to that produced by the natural object. However, species differ in the spectral tuning of
their photoreceptors, so a faithful colour rendition for a human is unlikely to be achieved for another species. This problem
is discussed with special reference to birds, a taxon renown for its colourfulness and frequent use in behavioural experiments
but which has a very different colour vision from that of humans. We stress that the major pitfalls that can arise when using
video playback with avian subjects can also occur in ’normal’ behavioural experiments. However, the problems of faithful colour
rendition are particularly severe with video, and the major benefits that the technology brings will only be realised under
a limited range of circumstances, with careful validation experiments.
Received: 24 January 2000 / Received in revised form: 28 March 2000 / Accepted: 1 April 2000 相似文献
4.
We developed a novel disposable bioassay device based on the fluorescein isothiocyanate-labelled low-density lipoprotein-uptake
activity of human hepatoblastoma Hep G2 cells. The cells were cultured in porous microcarriers at a high cell density and
packed in a filter tip that has a hydrophobic membrane. Upon evaluation of water samples, the culture medium was decanted
by pipetting it down with a micropipet, and the samples were then introduced to the cell-immobilizing part of the tip only
by pipetting them up after mixing them with ×10 concentrated culture medium. The new device enabled us to detect almost the
same toxicity levels of river water within 2 h of exposure as those detected by a conventional 48-h cell-survival assay. This
is the first bioassay device for the rapid on-site evaluation of environmental waters using cultured human cells, and therefore
promising for water-quality management based on risk to humans.
Received: 17 September 1999 / Received revision: 8 March 2000 / Accepted: 10 March 2000 相似文献
5.
In this article we review the evidence for and against recombination in human mtDNA. If recombination occurs, there needs
to be a route by which genetic material can incorporate itself into the mitochondrial genome, and hence between mitochondrial
lineages. We review the evidence for possible routes and then review the current state of the population genetic evidence
for recombination. We conclude that there is no firmly established route by which recombination can occur, and that while
some of the population genetic evidence is suggestive of recombination, it is far from conclusive.
Received: 22 November 2000 / Accepted: 16 February 2001 相似文献
6.
Ke Y Ye K Grossniklaus HE Archer DR Joshi HC Kapp JA 《Cancer immunology, immunotherapy : CII》2000,49(4-5):217-225
Noscapine, a phthalideisoquinoline alkaloid derived from opium, has been used as an oral anti-tussive agent and has shown
very few toxic effects in animals or humans. Recently, we reported that noscapine binds stoichiometrically to tubulin and
promotes microtubule polymerization. Noscapine causes growth arrest of tumor cells in mitosis and induces apoptosis of tumor
cells in vitro. Previous experiments also showed that noscapine has potent antitumor activity in mice when administered parenterally
or by gastric lavage. Here, we report that the anti-mitotic effect was specific to noscapine since closely related compounds
did not inhibit the growth of a lymphoma cell line. In addition, noscapine was shown to be effective in reducing the growth
of the lymphoma and increasing the survival of tumor-bearing mice when administered in the drinking water. It is noteworthy
that, noscapine showed little or no toxicity to kidney, liver, heart, bone marrow, spleen or small intestine at tumor-suppressive
doses. Furthermore, oral noscapine did not inhibit primary immune responses, which are critically dependent upon proliferation
of lymphoid cells. Thus, our results indicate that noscapine has the potential to be an effective chemotherapeutic agent for
the treatment of human cancer.
Received: 20 October 1999 / Accepted: 10 February 2000 相似文献
7.
Kanazawa J Ohta S Shitara K Fujita F Fujita M Hanai N Akinaga S Okabe M 《Cancer immunology, immunotherapy : CII》2000,49(4-5):253-258
KM871 is a chimeric antibody recognizing ganglioside GD3, which is one of the major gangliosides expressed on the cell surface
of human tumors of neuroectodermal origin. This study demonstrates the antitumor activity of KM871 against human melanoma
xenografts in nude mice, and analyzes the effector function operating in mice. In a well-established tumor model, KM871 showed
antitumor activity against H-15 and SK-MEL-28 human melanoma but not against H-187 and G361 human melanoma when administered
intravenously 5 days/week for 2 weeks. The G361 tumor became sensitive when KM871 was first administered on the day of tumor
inoculation. In this assay, it was observed that almost all the mice were tumor-free, but a few mice developed tumors. Therefore,
we examined the amount and expression pattern of GD3 antigen on G361 tumors escaping from KM871 treatment, but no change was
observed. Next we examined the optimal administration schedule for KM871 in mice, using H-15 melanoma. KM871 showed antitumor
activity when administered intravenously either 5 days/week for 2 weeks or three biweekly doses. However, the effect of the
former schedule was stronger than three biweekly doses. To compare the effector function in humans and mice, we studied the
complement-mediated cytotoxicity, antibody-dependent cell-mediated cytotoxicity and antibody-dependent macrophage-mediated
cytotoxicity of KM871 using complement or effector cells prepared from humans and mice. It was found that the antibody-dependent
cell-mediated cytotoxicity exerted by polymorphonuclear cells and antibody-dependent macrophage-mediated cytotoxicity were
the only antitumor mechanism of KM871 in mice. However their action was very weak compared with that in humans, and complement-mediated
cytotoxicity, which was strong in humans, was not observed in mice. Therefore, the antitumor activity of KM871 against human
melanomas evaluated by the nude mouse model might be underestimated. These results indicate that KM871 shows good antitumor
activity against GD3-positive human melanoma and the antitumor activity expected in humans might be superior to that of the
nude mouse model.
Received: 10 July 1999 / Accepted: 21 January 2000 相似文献
8.
In this paper, we identify a mechanism for chaos in the presence of noise. In a study of the SEIR model, which predicts epidemic
outbreaks in childhood diseases, we show how chaotic dynamics can be attained by adding stochastic perturbations at parameters
where chaos does not exist apriori. Data recordings of epidemics in childhood diseases are still argued as deterministic chaos.
There also exists noise due to uncertainties in the contact parameters between those who are susceptible and those who are
infected, as well as random fluctuations in the population. Although chaos has been found in deterministic models, it only
occurs in parameter regions that require a very large population base or other large seasonal forcing. Our work identifies
the mechanism whereby chaos can be induced by noise for realistic parameter regions of the deterministic model where it does
not naturally occur.
Received: 13 October 2000 / Revised version: 15 May 2001 / Published online: 7 December 2001 相似文献
9.
This article describes the organisation of song in the serin (Serinus serinus) and analyses its variation among individuals. Serins have a repertoire of about 50 complex syllables that are sung at a
very fast rate and in a very stereotyped order, forming discrete songs. Songs are high pitched for the serin’s body size.
Song organisation is circular, with a limited number of starting points. Songs can stop at any point in their cycling. Within
songs there are trilled sections and fast, non-repeated sections that account for the greatest part of songs. These two modes
of singing also differ in average inter-element intervals and probably in their respiratory kinematics. Bird repertoire size
was measured and the difficulties of measuring it in this species are discussed. Repertoires are individually specific and
have a variable amount of syllable sharing with other birds. We found evidence for geographical variation in the composition
of repertoires. Considering our current knowledge of song in carduelines, the stereotyped and circular nature of serin song
appear to be unique within this group of birds.
Received: 30 May 2000 / Received in revised from: 14 August 2000 / Accepted: 12 September 2000 相似文献
10.
Effects of ENU dosage on mouse strains 总被引:15,自引:0,他引:15
Monica J. Justice Don A. Carpenter Jack Favor Angelika Neuhauser-Klaus Martin Hrabé de Angelis Dian Soewarto Amy Moser Sabine Cordes Darla Miller Verne Chapman John S. Weber Eugene M. Rinchik Patricia R. Hunsicker William L. Russell Vernon C. Bode 《Mammalian genome》2000,11(7):484-488
The germline supermutagen, N-ethyl-N-nitrosourea (ENU), has a variety of effects on mice. ENU is a toxin and carcinogen as well as a mutagen, and strains differ
in their susceptibility to its effects. Therefore, it is necessary to determine an appropriate mutagenic, non-toxic dose of
ENU for strains that are to be used in experiments. In order to provide some guidance, we have compiled data from a number
of laboratories that have exposed male mice from inbred and non-inbred strains or their F1 hybrids to ENU. The results show that most F1 hybrid animals tolerate ENU well, but that inbred strains of mice vary in their longevity and in their ability to recover
fertility after treatment with ENU.
Received: 11 February 2000 / Accepted: 11 February 2000 相似文献
11.
In the mouse, Peg1/Mest is widely expressed in mesoderm-derived tissues. In separate studies, it has been shown to be maternally imprinted, that
is, only the paternally inherited allele is active in mice and in humans. Here, we provide evidence that Peg1/Mest is expressed at very low levels in all tissues of adult mice as assessed by RT-PCR. Moreover, by using species-specific polymorphisms
in the Peg1/Mest sequence we can demonstrate that in adult mice the gene remains imprinted in all of these tissues.
Received: 24 November 1997 / Accepted: 11 February 1998 相似文献
12.
M. Mar Albà Mauro F. Santibáñez-Koref John M. Hancock 《Journal of molecular evolution》2001,52(3):249-259
Polyglutamine repeats within proteins are common in eukaryotes and are associated with neurological diseases in humans. Many
are encoded by tandem repeats of the codon CAG that are likely to mutate primarily by replication slippage. However, a recent
study in the yeast Saccharomyces cerevisiae has indicated that many others are encoded by mixtures of CAG and CAA which are less likely to undergo slippage. Here we
attempt to estimate the proportions of polyglutamine repeats encoded by slippage-prone structures in species currently the
subject of genome sequencing projects. We find a general excess over random expectation of polyglutamine repeats encoded by
tandem repeats of codons. We nevertheless find many repeats encoded by nontandem codon structures. Mammals and Drosophila display extreme opposite patterns. Drosophila contains many proteins with polyglutamine tracts but these are generally encoded by interrupted structures. These structures
may have been selected to be resistant to slippage. In contrast, mammals (humans and mice) have a high proportion of proteins
in which repeats are encoded by tandem codon structures. In humans, these include most of the triplet expansion disease genes.
Received: 17 August 2000 / Accepted: 20 November 2000 相似文献
13.
Friesecke I Beyrer K Wedel R Reimers K Fliedner TM 《Radiation and environmental biophysics》2000,39(3):213-217
Overexposure of humans to ionizing radiation has occurred worldwide in the past and will surely occur again in the future.
In order to allow an effective radiation accident management, it is consequently necessary to be prepared for such emergency
situations and to improve means and ways to help people suffering from radiation-induced health impairments. Such approaches
should rely on knowledge and experience gained from previous radiation incidents. A prerequisite for any scientific evaluation
and comparison of information related to radiation accidents is to collect data in a standardized way. Therefore, the SEARCH
database (System for Evaluation and Archiving of Radiation accidents based on Case Histories) has been developed in our department
and implemented as an Oracle 8.0 database containing to date more than 800 case histories. The use of this registry is so
far limited to active contributors and requires each contributor to sign a cooperation agreement. More information is available
under http://www.faw.uni-ulm.de/radmed/.
Received: 7 February 2000 / Accepted: 8 May 2000 相似文献
14.
Fish peptones from tuna, cod, salmon, and unspecified fish were compared with a casein one by using a new method based on
Gompertz modeling of microbial growth. Cumulative results obtained from six species of bacteria, yeasts, and fungi showed
that, in most cases, these fish peptones are very effective. Nevertheless, this study raised some questions about the standardization
of fish raw material, the enzymatic hydrolysis of fish proteins, and the composition of the culture medium used for testing
the peptones.
Received: 15 June 2000 / Accepted: 17 July 2000 相似文献
15.
Depth cues, behavioural context, and natural illumination: some potential limitations of video playback techniques 总被引:2,自引:0,他引:2
J. Zeil 《Acta ethologica》2000,3(1):39-48
By expanding on issues raised by D’Eath (1998), I address in this article three aspects of vision that are difficult to reproduce
in the video- and computer-generated images used in experiments, in which images of conspecifics or of predators are replayed
to animals. The lack of depth cues derived from binocular stereopsis, from accommodation, and from motion parallax may be one of the reasons why animals do
not respond to video displays in the same way as they do to real conspecifics or to predators. Part of the problem is the
difficulty of reproducing the closed-loop nature of natural vision in video playback experiments. Every movement an animal
makes has consequences for the pattern of stimulation on its retina and this ”optic flow” in turn carries information about
both the animal’s own movement and about the three-dimensional structure of the environment. A further critical issue is the
behavioural context that often determines what animals attend to but that may be difficult to induce or reproduce in an experimental setting.
I illustrate this point by describing some visual behaviours in fiddler crabs, in which social and spatial context define
which part of the visual field a crab attends to and which visual information is used to guide behaviour. I finally mention
some aspects of natural illumination that may influence how animals perceive an object or a scene: shadows, specular reflections, and polarisation reflections.
Received: 23 November 1999 / Received in revised form: 9 February 2000 / Accepted: 10 February 2000 相似文献
16.
Dinoflagellate nuclear SSU rRNA phylogeny suggests multiple plastid losses and replacements 总被引:17,自引:0,他引:17
Saldarriaga JF Taylor FJ Keeling PJ Cavalier-Smith T 《Journal of molecular evolution》2001,53(3):204-213
Dinoflagellates are a trophically diverse group of protists with photosynthetic and non-photosynthetic members that appears
to incorporate and lose endosymbionts relatively easily. To trace the gain and loss of plastids in dinoflagellates, we have
sequenced the nuclear small subunit rRNA gene of 28 photosynthetic and four non-photosynthetic species, and produced phylogenetic
trees with a total of 81 dinoflagellate sequences. Patterns of plastid gain, loss, and replacement were plotted onto this
phylogeny. With the exception of the apparently early-diverging Syndiniales and Noctilucales, all non-photosynthetic dinoflagellates
are very likely to have had photosynthetic ancestors with peridinin-containing plastids. The same is true for all dinoflagellates
with plastids other than the peridinin-containing plastid: their ancestors have replaced one type of plastid for another,
in some cases most likely through a non-photosynthetic intermediate. Eight independent instances of plastid loss and three
of replacement can be inferred from existing data, but as more non-photosynthetic lineages are characterized these numbers
will surely grow.
Received: 25 September 2000 / Accepted: 24 April 2001 相似文献
17.
Marín I Fares MA González-Candelas F Barrio E Moya A 《Journal of molecular evolution》2001,52(1):17-28
We describe a new procedure to determine whether regional alterations in the evolutionary constraints imposed on paralogous
proteins have occurred. We used as models the A and B (alternatively called α and β) subunits of V/F/A-ATPases, originated
by a gene duplication more than 3 billion years ago. Changes associated to three major splits (eubacteria versus Archaea-eukaryotes;
Archaea versus eukaryotes; and among free-living bacteria and symbiotic mitochondria) were studied. Only in the first case,
when we compared eubacterial or mitochondrial F-ATPases versus eukaryotic vacuolar V-ATPases or archaeal A-ATPases, constraint
changes were observed. Modifications in the degree of regional constraining were not detected for the other two types of comparisons
(V-ATPases versus A-ATPases and within F-ATPases, respectively). When the rates of evolution of the two subunits were compared,
it was found that F-ATPases regulatory subunits evolved faster than catalytic subunits, but the opposite was true for A- and
V-ATPases. Our results suggest that, even for universal and essential proteins, selective constraints may be occasionally
altered. On the other hand, in some cases no changes were detected after periods of more than 2.2 billion years.
Received: 24 February 2000 / Accepted: 12 August 2000 相似文献
18.
Improvement of microbial strains and fermentation processes 总被引:20,自引:0,他引:20
Improvement of microbial strains for the over-production of industrial products has been the hallmark of all commercial fermentation
processes. Conventionally, strain improvement has been achieved through mutation, selection, or genetic recombination. Over-production
of primary or secondary metabolites is a complex process, and successful development of improved strains requires a knowledge
of physiology, pathway regulation and control, and the design of creative screening procedures. In addition, it requires mastery
of the fermentation process for each new strain, as well as sound engineering know-how for media-optimization and the fine-tuning
of process conditions. This review focuses on the various options that may be employed to improve microbial strains and addresses
the complex problems of screening, the tools and technology behind the selection of targeted organisms, and the importance
of process optimization. Furthermore, this review discusses new and emerging technologies and designing optimized media for
tracking mutants with enhanced productivity or other desired attributes.
Received: 7 February 2000 / Received revision: 2 May 2000 / Accepted: 2 May 2000 相似文献
19.
Pank M Stanhope M Natanson L Kohler N Shivji M 《Marine biotechnology (New York, N.Y.)》2001,3(3):231-240
Many commercially exploited carcharhinid sharks are difficult to identify to species owing to extensive morphological similarities.
This problem is severely exacerbated when it comes to identifying detached shark fins, and the finless and headless shark
carasses typically sold in markets. To assist in the acquisition of urgently needed conservation and management data on shark
catch and trade, we have developed a highly streamlined approach based on multiplex polymerase chain reaction (PCR) that uses
species-specific primers derived from nuclear ribosomal ITS2 sequences to achieve rapid species identification of shark body
parts. Here we demonstrate the utility of this approach for identifying fins and flesh from two globally distributed, morphologically
very similar carcharhinid sharks (Carcharhinus obscurus and Carcharhinus plumbeus) intensively targeted in fisheries worldwide, and often confused for each other even as whole animals. The assay is conducted
in a 4-primer multiplex format that is structured to simultaneously achieve the following efficiency and cost-reduction objectives:
it requires only a single-tube amplification reaction for species diagnosis, it incorporates an internal positive control
to allow detection of false-negative results, and it is novel in that it allows species identification even when DNAs from
two species are combined in the same tube during the PCR reaction. The latter innovation reduces the required effort for screening
a set of unknown samples by 50%. The streamlined approach illustrated here should be amenable for use in a shark conservation
and management context where large numbers of samples typically need to be screened; the approach shown may also provide a
model for a rapid diagnostic method applicable to species identification in general.
Received September 15, 2000; accepted December 15, 2000 相似文献
20.
Multiple mechanisms of immune evasion can coexist in melanoma tumor cell lines derived from the same patient 总被引:2,自引:0,他引:2
Real LM Jimenez P Kirkin A Serrano A García A Cantón J Zeuthen J Garrido F Ruiz-Cabello F 《Cancer immunology, immunotherapy : CII》2001,49(11):621-628
Progressive tumor growth may be associated with suppression of the immune response. Many different mechanisms may contribute
to immune evasion. We investigated some of these mechanisms in melanoma cells lines generated from two patients. These cell
lines show a complex pattern of altered HLA expression; however, the resulting phenotype did not satisfactorily explain the
simultaneous evasion of T and NK cell cytotoxicity. Two additional alterations have now been detected in these melanoma cell
lines: (1) resistance to FAS-induced apoptosis caused by defective FAS gene expression, and (2) constitutive expression of
immunosuppressive cytokines. Our results show that several of the major mechanisms for immune evasion may coexist in a single
tumor. This suggests that tumor progression may give rise to an extremely resistant phenotype, which may be an impediment
to some immunotherapeutic strategies. We hypothesize that the simultaneous presence of several mechanisms involved in tumor
immune evasion must be the result of progressive selection of characteristics that are advantageous for tumor survival in
a competent host. Our findings do not support the possibility that FASL expression is a common mechanism of evasion of immune
response in melanoma cells.
Received: 27 January 2000 / Accepted: 28 August 2000 相似文献