排序方式: 共有79条查询结果,搜索用时 46 毫秒
61.
Trichas G Smith AM White N Wilkins V Watanabe T Moore A Joyce B Sugnaseelan J Rodriguez TA Kay D Baker RE Maini PK Srinivas S 《PLoS biology》2012,10(2):e1001256
The visceral endoderm (VE) is a simple epithelium that forms the outer layer of the egg-cylinder stage mouse embryo. The anterior visceral endoderm (AVE), a specialised subset of VE cells, is responsible for specifying anterior pattern. AVE cells show a stereotypic migratory behaviour within the VE, which is responsible for correctly orientating the anterior-posterior axis. The epithelial integrity of the VE is maintained during the course of AVE migration, which takes place by intercalation of AVE and other VE cells. Though a continuous epithelial sheet, the VE is characterised by two regions of dramatically different behaviour, one showing robust cell movement and intercalation (in which the AVE migrates) and one that is static, with relatively little cell movement and mixing. Little is known about the cellular rearrangements that accommodate and influence the sustained directional movement of subsets of cells (such as the AVE) within epithelia like the VE. This study uses an interdisciplinary approach to further our understanding of cell movement in epithelia. Using both wild-type embryos as well as mutants in which AVE migration is abnormal or arrested, we show that AVE migration is specifically linked to changes in cell packing in the VE and an increase in multi-cellular rosette arrangements (five or more cells meeting at a point). To probe the role of rosettes during AVE migration, we develop a mathematical model of cell movement in the VE. To do this, we use a vertex-based model, implemented on an ellipsoidal surface to represent a realistic geometry for the mouse egg-cylinder. The potential for rosette formation is included, along with various junctional rearrangements. Simulations suggest that while rosettes are not essential for AVE migration, they are crucial for the orderliness of this migration observed in embryos. Our simulations are similar to results from transgenic embryos in which Planar Cell Polarity (PCP) signalling is disrupted. Such embryos have significantly reduced rosette numbers, altered epithelial packing, and show abnormalities in AVE migration. Our results show that the formation of multi-cellular rosettes in the mouse VE is dependent on normal PCP signalling. Taken together, our model and experimental observations suggest that rosettes in the VE epithelium do not form passively in response to AVE migration. Instead, they are a PCP-dependent arrangement of cells that acts to buffer the disequilibrium in cell packing generated in the VE by AVE migration, enabling AVE cells to migrate in an orderly manner. 相似文献
62.
Ericson NG Kulawiec M Vermulst M Sheahan K O'Sullivan J Salk JJ Bielas JH 《PLoS genetics》2012,8(6):e1002689
Genome instability is regarded as a hallmark of cancer. Human tumors frequently carry clonally expanded mutations in their mitochondrial DNA (mtDNA), some of which may drive cancer progression and metastasis. The high prevalence of clonal mutations in tumor mtDNA has commonly led to the assumption that the mitochondrial genome in cancer is genetically unstable, yet this hypothesis has not been experimentally tested. In this study, we directly measured the frequency of non-clonal (random) de novo single base substitutions in the mtDNA of human colorectal cancers. Remarkably, tumor tissue exhibited a decreased prevalence of these mutations relative to adjacent non-tumor tissue. The difference in mutation burden was attributable to a reduction in C:G to T:A transitions, which are associated with oxidative damage. We demonstrate that the lower random mutation frequency in tumor tissue was also coupled with a shift in glucose metabolism from oxidative phosphorylation to anaerobic glycolysis, as compared to non-neoplastic colon. Together these findings raise the intriguing possibility that fidelity of mitochondrial genome is, in fact, increased in cancer as a result of a decrease in reactive oxygen species-mediated mtDNA damage. 相似文献
63.
64.
Jeffrey A. Harvey Bertanne Visser Cecile Le Lann Jetske de Boer Jacintha Ellers Rieta Gols 《Evolutionary biology》2014,41(1):134-144
Closely related species in nature often show similarities in suites of direct and indirect traits that reveal aspects of their phylogenetic history. Here we tested how common descent affects trait evolution in several closely related parasitoid species in the genera Cotesia and Microplitis (Hymenoptera: Braconidae: Microgastrinae) by comparing development, resource use and allocation into reproduction and maintenance. Parasitoids in these genera exhibit traits, like haemolymph feeding as larvae and external pupation that are rare in most parasitoid lineages. The growth of parasitized hosts was reduced by 90 % compared with healthy hosts, and maximum host size depended to a large extent on adult parasitoid size. Development time was longer in the more generalist parasitoids than in the specialists. Adult body mass was sexually dimorphic in all Cotesia species, with females being larger, but not in Microplitis spp. In contrast, in one of the Microplitis species males were found to be the larger sex. Egg load dynamics during the first 6 days after emergence were highly variable but egg number was typically higher in Cotesia spp. compared to Microplitis spp. Longevity in the various species was only greater in female than in male wasps in two Microplitis sp. There was a clear inverse relationship between resource use and allocation, e.g. maximum egg load and longevity, in these parasitoids. Our results reveal that adaptation to constraints imposed by host quality and availability has resulted in trait convergence and divergence at the species, genus and subfamily level. 相似文献
65.
Maartje Liefting Ary A. Hoffmann Jacintha Ellers 《Evolution; international journal of organic evolution》2014,68(5):1544-1547
Rocha and Klaczko emphasize the general complexity of reaction norm shape and caution that ignoring such complexity can be misleading when forcing nonlinear reaction norms into linear shapes. They refer to our article on differences in plasticity of Drosophila serrata populations along a latitudinal gradient as an example of a misleading simplifying approach. However, their claim that an artifact is introduced into our analyses by calculating developmental rate as the reciprocal of development time (rate = time?1) is based on a misunderstanding of the mathematical properties of the thermal developmental rate reaction norm. Here we discuss why developmental rate is a suitable measure for our study and under which circumstances it is appropriate to describe developmental rate by a linear model. 相似文献
66.
Maartje Liefting Ary A. Hoffmann Jacintha Ellers 《Evolution; international journal of organic evolution》2009,63(8):1954-1963
The phenotypic plasticity of traits, defined as the ability of a genotype to express different phenotypic values of the trait across a range of environments, can vary between habitats depending on levels of temporal and spatial heterogeneity. Other traits can be insensitive to environmental perturbations and show environmental canalization. We tested levels of phenotypic plasticity in diverse Drosophila serrata populations along a latitudinal cline ranging from a temperate, variable climate to a tropical, stable climate by measuring developmental rate and size-related traits at three temperatures (16°C, 22°C, and 28°C). We then compared the slopes of the thermal reaction norms among populations. The 16–22°C part of the reaction norms for developmental rate was flatter (more canalized) for the temperate populations than for the tropical populations. However, slopes for the reaction norms of the two morphological traits (wing size, wing:thorax ratio), were steeper (more plastic) in the temperate versus the tropical populations over the entire thermal range. The different latitudinal patterns in plasticity for developmental rate and the morphological traits may reflect contrasting selection pressures along the tropical–temperate thermal gradient. 相似文献
67.
Background
Sexual conflicts between mating partners can strongly impact the evolutionary trajectories of species. This impact is determined by the balance between the costs and benefits of mating. However, due to sex-specific costs it is unclear how costs compare between males and females. Simultaneous hermaphrodites offer a unique opportunity to determine such costs, since both genders are expressed concurrently. By limiting copulation of focal individuals in pairs of pond snails (Lymnaea stagnalis) to either the male role or the female role, we were able to compare the fecundity of single sex individuals with paired hermaphrodites and non-copulants. Additionally, we examined the investment in sperm and seminal fluid of donors towards feminized snails and hermaphrodites. 相似文献68.
Evolutionary community ecology is an emerging field of study that includes evolutionary principles such as individual trait
variation and plasticity of traits to provide a more mechanistic insight as to how species diversity is maintained and community
processes are shaped across time and space. In this review we explore phenotypic plasticity in functional traits and its consequences
at the community level. We argue that resource requirement and resource uptake are plastic traits that can alter fundamental
and realised niches of species in the community if environmental conditions change. We conceptually add to niche models by
including phenotypic plasticity in traits involved in resource allocation under stress. Two qualitative predictions that we
derive are: (1) plasticity in resource requirement induced by availability of resources enlarges the fundamental niche of
species and causes a reduction of vacant niches for other species and (2) plasticity in the proportional resource uptake results
in expansion of the realized niche, causing a reduction in the possibility for coexistence with other species. We illustrate
these predictions with data on the competitive impact of invasive species. Furthermore, we review the quickly increasing number
of empirical studies on evolutionary community ecology and demonstrate the impact of phenotypic plasticity on community composition.
Among others, we give examples that show that differences in the level of phenotypic plasticity can disrupt species interactions
when environmental conditions change, due to effects on realized niches. Finally, we indicate several promising directions
for future phenotypic plasticity research in a community context. We need an integrative, trait-based approach that has its
roots in community and evolutionary ecology in order to face fast changing environmental conditions such as global warming
and urbanization that pose ecological as well as evolutionary challenges. 相似文献
69.
Effect of light quality and 5-azacytidine on genomic methylation and stem elongation in two ecotypes of Stellaria longipes 总被引:4,自引:0,他引:4
Gurminder S. Tatra Jacintha Miranda Chendanda C. Chinnappa David M. Reid 《Physiologia plantarum》2000,109(3):313-321
Changes in cytosine methylation are known to occur in response to various environmental stimuli, therefore, we looked at methylation changes in relation to stem elongation. More specifically, we investigated the response of genomic cytosine methylation to irradiance-mediated plasticity of stem elongation in two ecotypes of Stellaria longipes . Ramets of S. longipes were grown under high and low ratios of red/far-red light (F/FR; 3.7 and 0.7, respectively). Stem elongation and methylated cytosine content were measured over a period of 7 days. Ramets of S. longipes demonstrated the highest level of demethylation after 4 days of long-day warm (LDW) treatment, which coincides with the first day of rapid stem elongation initiation. The extent of demethylation associated with day 4 depended upon the relative ratio of R/FR light. In particular, those plants treated with low R/FR light ratios showed a lower level of methylation, and were taller than the high R/FR light grown counterparts. In addition, prairie ecotype plants demonstrated lower day 4 methylation levels, as well as longer day 7 stem lengths, than the alpine ecotype plants within the same R/FR light treatments. To investigate if the degree of methylation was a crucial factor in controlling the stem elongation response, ramets of both alpine and prairie plants were grown in MS media supplemented with 5-azacytidine (5-AzaC), and grown for 14 days under a R/FR ratio of 3.7 and two different PAR values. 5-AzaC treatments demonstrated that the prairie ecotype plants required greater doses of 5-AzaC, and thus lower methylation levels, than the alpine ecotype plants in order to promote maximal stem elongation. These observations suggest that DNA demethylation is involved in the shade-avoidance response. 相似文献
70.
Muriel E de Boer Sandra Berg Martijn JTN Timmermans Johan T den Dunnen Nico M van Straalen Jacintha Ellers Dick Roelofs 《BMC molecular biology》2011,12(1):11