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871.
Marengo B Bottini C La Porta CA Domenicotti C Tessitore L 《Biochemical and biophysical research communications》2006,346(1):234-241
Phosphatidylethanolamine N-methyltransferase (PEMT) is the enzyme that converts phosphatidylethanolamine (PE) into phosphatidylcholine. We have previously shown that PEMT suppressed hepatoma growth by triggering apoptosis. We investigate whether PEMT controlled cell death and cell proliferation triggered by fasting/refeeding and whether it is a marker of early preneoplastic lesions. The induction of programmed cell death and suppression of cell proliferation by fasting were associated with enhanced PEMT expression and activity, and with a decrease in CTP:phosphocholine cytidylyltransferase expression. Refeeding returned the liver growth and expression of CTP:phosphocholine cytidylyltransferase to control levels, while the expression of PEMT decreased to below control values. After DENA administration, PEMT protein, evaluated by Western blotting, slightly increased, but it remained below control levels. The treatment with 20 mg/kg DENA to refed rats induced the appearance of initiated hepatocytes that were negative for PEMT expression. Present findings indicate that PEMT is a novel tumour marker for early liver preneoplastic lesions. 相似文献
872.
Boggs CL Holdren CE Kulahci IG Bonebrake TC Inouye BD Fay JP McMillan A Williams EH Ehrlich PR 《The Journal of animal ecology》2006,75(2):466-475
1. The causes of lagged population and geographical range expansions after species introductions are poorly understood, and there are relatively few detailed case studies. 2. We document the 29-year history of population dynamics and structure for a population of Euphydryas gillettii Barnes that was introduced to the Colorado Rocky Mountains, USA in 1977. 3. The population size remained low (< 200 individuals) and confined to a single habitat patch (approximately 2.25 ha) to 1998. These values are similar to those of many other populations within the natural geographical range of the species. 4. However, by 2002 the population increased dramatically to > 3000 individuals and covered approximately 70 ha, nearly all to the south of the original site. The direction of population expansion was the same as that of predominant winds. 5. By 2004, the butterfly's local distribution had retracted mainly to three habitat patches. It thus exhibited a 'surge/contraction' form of population growth. Searches within 15 km of the original site yielded no other new populations. 6. In 2005, butterfly numbers crashed, but all three habitat patches remained occupied. The populations within each patch did not decrease in the same proportions, suggesting independent dynamics that are characteristic of metapopulations. 7. We postulate that this behaviour results, in this species, in establishment of satellite populations and, given appropriate habitat structure, may result in lagged or punctuated expansions of introduced populations. 相似文献
873.
874.
We investigate the speed of invasion waves for a single species generated by stochastic short- and/or long-distance colonizations
in a time-continuous cellular automaton (CA) model on a two-dimensional homogenous landscape. By simulating the CA models,
we demonstrate that stochasticity can dramatically increase the speed of invasion compared to the corresponding deterministic
CA model or the corresponding one-dimensional stochastic CA model. To explain this phenomenon, we first develop a mathematical
model for the invasion involving only short-distance colonization (i.e., colonization only occurs from the eight adjacent
cells), and present several approximation methods for solving the model. Our analyses show that the increased wave speed in
the stochastic model is due to irregularity in the shape of the wavefront. Further extension of this model to include long-distance
colonization demonstrates that stochasticity influences speeds to even greater extents in this case. Using dimension analysis,
we deduced a semi-empirical formula for the speed as a function of three parameters intrinsic to short- and long-distance
colonization, which agrees well with simulation results. Based on these results, we discuss how important stochasticity in
colonization and spatial dimensionality are in the acceleration of invasion speed. 相似文献
875.
David Bart David Burdick Randolph Chambers Jean Marie Hartman 《Wetlands Ecology and Management》2006,14(1):53-65
Efforts to manage or prevent Phragmites australis invasion in salt and brackish marshes are complicated by the lack of a general causal role for specific human activities.
The pattern of invasion within a marsh differs among sites, and each may have different causal histories. A review of the
literature finds three establishment/invasion patterns: (1) from stands established on ditch- or creek-bank levees toward
interior portions of high marshes, (2) from stands along upland borders toward high marsh interiors, and (3) centroid spread
from high marsh stands established in ostensibly random locations. Each invasion pattern seems to have different anthropogenic
precursors, therefore preventing generalizations about the role of any one human activity in all sites. However, historical
and experimental evidence suggests that regardless of invasion pattern, establishment is much more likely at sites where rhizomes
are buried in well-drained, low salinity marsh areas. Any human activity that buries large rhizomes, increases drainage, or
lowers salinity increases chances of establishing invasive clones. To integrate these patterns and improve our understanding
of the rapid spread of Phragmites, recent evidence has been synthesized into a dichotomous flow chart which poses questions about current site conditions and
the potential for proposed activities to change site conditions that may facilitate invasion. This simple framework could
help managers assess susceptibility and take preventative measures in coastal marshes before invasion occurs or before removal
becomes very expensive. 相似文献
876.
A role of LIM kinase 1/cofilin pathway in regulating endocytic trafficking of EGF receptor in human breast cancer cells 总被引:2,自引:2,他引:0
Nishimura Y Yoshioka K Bernard O Bereczky B Itoh K 《Histochemistry and cell biology》2006,126(5):627-638
We have previously shown that overexpression of LIM kinase1 (LIMK1) resulted in a marked retardation of the internalization of the receptor-mediated endocytic tracer, Texas red-labeled epidermal growth factor (EGF) in low-invasive human breast cancer cell MCF-7. We thereby postulate that LIMK1 signaling plays an important role in the regulation of ligand-induced endocytosis of EGF receptor (EGFR) in tumor cells by reorganizing and influencing actin-filament dynamics. In the present study, we further assessed the effect of wild-type LIMK1, a kinase-deficient dominant negative mutant of LIMK1 (DN-LIMK1) and an active, unphosphorylatable cofilin mutant (S3A cofilin) on internalization of EGF-EGFR in MDA-MB-231, a highly invasive human breast cancer cell line. We demonstrate here that a marked delay in the receptor-mediated internalization of Texas red-labeled EGF was observed in the wild-type LIMK1 transfectants, and that most of the internalized EGF staining were accumulated within transferrin receptor-positive early endosomes even after 30 min internalization. In contrast, the expression of dominant-negative LIMK1 mutant rescued the efficient endocytosis of Texas red-EGF, and large amounts of Texas red-EGF staining already reached LIMPII-positive late endosomes/lysosomal vacuoles after 15 min internalization. We further analyzed the effect of S3A cofilin mutant on EGFR trafficking, and found an efficient delivery of Texas red-EGF into late endosomes/lysosomes at 15–30 min after internalization. Taken together, our novel findings presented in this paper implicate that LIMK1 signaling indeed plays a pivotal role in the regulation of EGFR trafficking through the endocytic pathway in invasive tumor cells. 相似文献
877.
Contrasting patterns in genetic diversity following multiple invasions of fresh and brackish waters 总被引:1,自引:1,他引:0
Biological invasions may combine the genetic effects of population bottlenecks and selection and thus provide valuable insight into the role of such processes during novel environmental colonizations. However, these processes are also influenced by multiple invasions, the number of individuals introduced and the degree of similarity between source and receiving habitats. The amphipod Gammarus tigrinus provides a useful model to assess these factors, as its invasion history has involved major environmental transitions. This species is native to the northwest Atlantic Ocean, although it invaded both brackish and freshwater habitats in the British Isles after introduction more than 65 years ago. It has also spread to similar habitats in Western Europe and, most recently, to Eastern Europe, the Baltic Sea, and the Laurentian Great Lakes. To examine sources of invasion and patterns of genetic change, we sampled populations from 13 native estuaries and 19 invaded sites and sequenced 542 bp of the mitochondrial COI gene. Strong native phylogeographical structure allowed us to unambiguously identify three allopatrically evolved clades (2.3-3.1% divergent) in invading populations, indicative of multiple introductions. The most divergent clades occurred in the British Isles and mainland Europe and were sourced from the St Lawrence and Chesapeake/Delaware Bay estuaries. A third clade was found in the Great Lakes and sourced to the Hudson River estuary. Despite extensive sampling, G. tigrinus did not occur in freshwater at putative source sites. Some European populations showed reduced genetic diversity consistent with bottlenecks, although selection effects cannot be excluded. The habitat distribution of clades in Europe was congruent with the known invasion history of secondary spread from the British Isles. Differences in salinity tolerance among lineages were suggested by patterns of habitat colonization by different native COI clades. Populations consisting of admixtures of the two invading clades were found principally at recently invaded fresh and brackish water sites in Eastern Europe, and were characterized by higher genetic diversity than putative source populations. Further studies are required to determine if these represent novel genotypes. Our results confirm that biological invasions need not result in diminished genetic diversity, particularly if multiple source populations, each with distinctive genetic composition, contribute to the founding populations. 相似文献
878.
Manoranjan Santra Sutapa Santra Cindi Roberts Rui Lan Zhang Michael Chopp† 《Journal of neurochemistry》2009,108(1):231-245
Doublecortin (DCX) is a microtubule (MT) binding protein that induces growth arrest at the G2–M phase of cell cycle in glioma and suppresses tumor xenograft in immunocompromised hosts. DCX expression was found in neuronal cells, but lacking in glioma cells. We tested the hypothesis that DCX inhibits glioma U87 cell mitosis and invasion. Our data showed that DCX synthesizing U87 cells underwent mitotic MT spindle catastrophe in a neurabin II dependent pathway. Synthesis of both DCX and neurabin II were required to induce apoptosis in U87 and human embryonic kidney 293T cells. In DCX expressing U87 cells, association of phosphorylated DCX with protein phosphatase-1 (PP1) in the cytosol disrupted the interaction between kinesin-13 and PP1 in the nucleus and yielded spontaneously active kinesin-13. The activated kinesin-13 caused mitotic MT catastrophe in spindle checkpoint. Phosphorylated-DCX induced depolymerization of actin filaments in U87 cells, down-regulated matrix metalloproteinases-2 and -9, and inhibited glioma U87 cell invasion in a neurabin II dependent pathway. Thus, localization of the DCX–neurabin II–PP1 complex in the cytosol of U87 tumor cells inhibited PP1 phosphatase activities leading to anti-glioma effects via (1) mitotic MT spindle catastrophe that blocks mitosis and (2) depolymerization of actin that inhibits glioma cell invasion. 相似文献
879.
Hua Guo† Feng Gu‡ Wenliang Li§ Baogang Zhang Ruifang Niu Li Fu‡ Ning Zhang Yongjie Ma 《Journal of neurochemistry》2009,109(1):203-213
Glioblastomas are the most aggressive forms of primary brain tumors with their tendency to invade surrounding healthy brain tissues, rendering them largely incurable. In this report, we used small-interference RNA technology to knock down the expression of protein kinase C (PKC) ζ, which resulted in specific and massive impairment of glioblastoma cell migration and invasion. We also explained the fundamental molecular processes of glioblastoma migration and invasion in which PKCζ is a participant. The silence of PKCζ expression likewise impaired the phosphorylation of LIN-11, Isl1 and MEC-3 protein domain kinase (LIMK) and cofilin, which is a critical step in cofilin recycling and actin polymerization. Consistent with the defects in cell adhesion, phosphorylation of integrin β1 was also dampened. Therefore, PKCζ regulated both cytoskeleton rearrangement and cell adhesion, which contributed to cell migration. Additionally, there was down-regulation of matrix metalloprotease-9 expression in siPKCζ/LN-229 cells, which coincided with decreased invasion both in vitro and in vivo. These results indicate that PKCζ is involved in the control of glioblastoma cell migration and invasion by regulating the cytoskeleton rearrangement, cell adhesion, and matrix metalloprotease-9 expression. Collectively, these findings suggest that PKCζ is a potential therapeutic target for glioblastoma infiltration. 相似文献
880.
BOHUMIL MANDÁK PETR ZÁKRAVSKÝ DANA KOÍNKOVÁ PETR DOSTÁL IVANA PLAKOVÁ 《Biological journal of the Linnean Society. Linnean Society of London》2009,98(3):596-607
Colonizing species are predicted to suffer from reductions in genetic diversity during founding events. Although there is no unique mode of reproduction that is characteristic of successful plant colonizers, many of them are predominantly self-fertilizing or apomictic species, and almost all outcrossing colonizers are self-compatible. Carduus acanthoides comprises a species of disturbed habitats with wind-dispersed seeds that colonizes open spaces of various sizes. Population genetic diversity was expressed by assessing patterns of variation at nine putatively neutral allozyme loci within and among 20 natural populations in its native distribution range in the Czech Republic. Overall, C. acanthoides displayed high levels of genetic diversity compared to other herbaceous plants. The percentage of polymorphic loci was 84.5, with values of 2.37, 0.330, and 0.364 for the mean number of alleles per polymorphic locus ( A ), observed heterozygosity ( H o ), and expected heterozygosity ( H e ), respectively. There was only weak evidence of inbreeding within populations ( f = 0.097) and very low genetic differentiation among populations ( θ = 0.085). Analyses of the data provide strong evidence for isolation-by-distance for the whole study area. Even the colonizing species, C. acanthoides , currently supports a substantial amount of allozyme variation at both the species and population levels. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 596–607. 相似文献