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31.
Cell migration entails the formation of cellular protrusions such as lamellipodia or filopodia, the growth of which is powered by the polymerisation of actin filaments abutting the plasma membrane. Specific Rho-GTPase subfamilies are able to drive different types of protrusions. However, significant crosstalk between Rho-family members and the interplay of distinct Rho-effectors regulating or modulating actin reorganization in protrusions complicate the picture of how precisely they are initiated and maintained. Here, we briefly sketch our current knowledge on structure and dynamics of different protrusions as well as their regulation by Rho-GTPases. We also comment on topical, unresolved controversies in the field, with special emphasis on the interrelation of different protrusion types, and on the composition of the nanomachineries driving them. 相似文献
32.
Shoji Kagami Maki Urushihara Shuji Kondo Klemens Lster Werner Reutter Toshiaki Tamaki Masanori Yoshizumi Yasuhiro Kuroda 《Experimental cell research》2001,268(2):274
Abnormal mesangial extracellular matrix remodeling by mesangial cells (MCs) is the hallmark of progressive glomerulonephritis (GN). We recently showed, using a type I collagen gel contraction assay, that α1β1 integrin-dependent MC adhesion and migration are necessary cell behaviors for collagen matrix remodeling. To further determine the mechanism of α1β1 integrin-mediated collagen remodeling, we studied the signaling pathways of MCs that participate in the regulation of collagen gel contraction. Immunoprecipitation and phosphotyrosine detection revealed that gel contraction is associated with the enhanced activity and phosphorylation of ERK1/2 by MCs. The tyrosine kinase inhibitors herbimycin and genistein inhibited collagen gel contraction dose dependently. Furthermore, targeting ERK1/2 activity with a MEK inhibitor, PD98059, and antisense ERK1/2 hindered gel contraction in a dose-dependent manner. Similar inhibitory effects on gel contraction and ERK1/2 phosphorylation were observed when MC-mediated gel contraction was performed in the presence of function-blocking anti-α1 or anti-β1 integrin antibodies. However, cell adhesion and migration assays indicated that PD98059 and antisense ERK1/2 blocked α1β1 integrin-dependent MC migration, but did not interfere with collagen adhesion, although there was a marked decrease in ERK1/2 phosphorylation and ERK1/2 protein expression in cell adhesion on type I collagen. None of the above could affect membrane expression of α1β1 integrin. These results suggested that ERK1/2 activation is critical for the α1β1 integrin-dependent MC migration necessary for collagen matrix reorganization. We therefore conclude that ERK1/2 may serve as a possible target for pharmacological inhibition of pathological collagen matrix formation in GN. 相似文献
33.
The winter diet and foraging range of gentoo penguins, Pygoscelis papua, were studied at Kidney Cove, Falkland Islands. The mean wet mass of the 56 stomach-content samples collected from May to October was 32.7ᇃ.4 g. The diet consisted generally of cephalopods, crustaceans and fish, as well as two other molluscs. Among the six cephalopod species identified, the commercially fished Patagonian squid, Loligo gahi, had the highest abundance and was also the main prey by reconstituted mass (53% of the total reconstituted mass). Lobster krill, Munida gregaria, one of five species of crustaceans, was the most abundant prey species by frequency of occurrence and by number (68% and 60%, respectively). Rock cod, Patagonotothen ramsayi, accounted for the majority of the fish diet with 34% of the total reconstituted mass. Most prey species identified in the winter diet were also abundant diet components during the breeding season. However, the known biology of the prey species and their rate of digestion indicated that, in winter, adults may forage further offshore than during the breeding season. This assumption was supported by the results obtained from two birds satellite-tracked during the study period. Both birds remained mainly in inshore waters and returned frequently ashore, but one penguin foraged up to 276 km from the coast. The differences in the foraging behaviour of the two birds were reflected in significant differences with regard to time spent underwater, distance travelled per day and calculated travelling speed. Furthermore, the progress of cohorts of L. gahi over the winter is consistent with results from life-cycle studies in this region and suggests that birds have been foraging in the feeding grounds of L. gahi. 相似文献
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Eukaryotic cells advance in phases of protrusion, pause and withdrawal. Protrusion occurs in lamellipodia, which are composed of diagonal networks of actin filaments, and withdrawal terminates with the formation of actin bundles parallel to the cell edge. Using correlated live-cell imaging and electron microscopy, we have shown that actin filaments in protruding lamellipodia subtend angles from 15-90 degrees to the front, and that transitions from protrusion to pause are associated with a proportional increase in filaments oriented more parallel to the cell edge. Microspike bundles of actin filaments also showed a wide angular distribution and correspondingly variable bilateral polymerization rates along the cell front. We propose that the angular shift of filaments in lamellipodia serves in adapting to slower protrusion rates while maintaining the filament densities required for structural support; further, we suggest that single filaments and microspike bundles contribute to the construction of the lamella behind and to the formation of the cell edge when protrusion ceases. Our findings provide an explanation for the variable turnover dynamics of actin filaments in lamellipodia observed by fluorescence speckle microscopy and are inconsistent with a current model of lamellipodia structure that features actin filaments branching at 70 degrees in a dendritic array. 相似文献
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Britas Klemens Eriksson Tjisse van der Heide Johan van de Koppel Theunis Piersma Henk W. van der Veer Han Olff 《Ecosystems》2010,13(5):752-764
Shallow soft-sediment systems are mostly dominated by species that, by strongly affecting sediment dynamics, modify their
local environment. Such ecosystem engineering species can have either sediment-stabilizing or sediment-destabilizing effects
on tidal flats. They interplay with abiotic forcing conditions (wind, tide, nutrient inputs) in driving the community structure
and generating spatial heterogeneity, determining the composition of different communities of associated species, and thereby
affecting the channelling of energy through different compartments in the food web. This suggests that, depending on local
species composition, tidal flats may have conspicuously different geomorphology and biological functions under similar external
conditions. Here we use a historical reconstruction of benthic production in the Wadden Sea to construct a framework for the
relationships between human impacts, ecosystem engineering and sediment dynamics. We propose that increased sediment disturbances
by human exploitation interfere with biological controls of sediment dynamics, and thereby have shifted the dominant compartments
of both primary and secondary production in the Wadden Sea, transforming the intertidal from an internally regulated and spatially
heterogeneous, to an externally regulated and spatially homogenous system. This framework contributes to the general understanding
of the interaction between biological and environmental control of ecosystem functioning, and suggests a general framework
for predicting effects of human impacts on soft-bottom ecosystems. 相似文献
39.
The majority of mammalian pre-mRNAs contains multiple introns that are excised prior to export and translation. After intron excision, ligated exon intermediates participate in subsequent intron excisions. However, exon ligation generates an exon of increased size, a feature of pre-mRNA splicing that can interfere with downstream splicing events. These considerations raise the question of whether unique mechanisms exist that permit efficient removal of introns neighboring ligated exons. Kinetic analyses of multiple intron-containing pre-mRNAs revealed that splicing is more efficient following an initial intron removal event, suggesting that either the recruitment of the exon junction complex (EJC) to ligated exons increases the efficiency of multiple intron excisions or that the initial definition of splice sites is sufficient to permit efficient splicing of introns neighboring ligated exons. Knockdown experiments show that the deposition of the EJC does not affect subsequent splicing kinetics. Instead, spliceosomal components that are not involved in the initial splicing event remain associated with the pre-mRNA to ensure efficient removal of neighboring introns. Thus, ligated exons do not require redefinition, providing an additional kinetic advantage for exon defined splice sites. 相似文献
40.
Susanna Marg Ulrike Winkler Marcello Sestu Mirko Himmel Madeleine Sch?nherr Janina B?r Amrit Mann Markus Moser Claudia T. Mierke Klemens Rottner Manfred Blessing Johannes Hirrlinger Wolfgang H. Ziegler 《PloS one》2010,5(7)