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101.
Keeling L Andersson L Schütz KE Kerje S Fredriksson R Carlborg O Cornwallis CK Pizzari T Jensen P 《Nature》2004,431(7009):645-646
Feather-pecking in domestic birds is associated with cannibalism and severe welfare problems. It is a dramatic example of a spiteful behaviour in which the victim's fitness is reduced for no immediate direct benefit to the perpetrator and its evolution is unexplained. Here we show that the plumage pigmentation of a chicken may predispose it to become a victim: birds suffer more drastic feather-pecking when the colour of their plumage is due to the expression of a wild recessive allele at PMEL17, a gene that controls plumage melanization, and when these birds are relatively common in a flock. These findings, obtained using an intercross between a domestic fowl and its wild ancestor, have implications for the welfare of domestic species and offer insight into the genetic changes associated with the evolution of feather-pecking during the early stages of domestication. 相似文献
102.
Li J Jiang T Mao JH Balmain A Peterson L Harris C Rao PH Havlak P Gibbs R Cai WW 《Nature genetics》2004,36(9):952-954
By analyzing genomic copy-number differences using high-resolution mouse whole-genome BAC arrays, we uncover substantial differences in regional DNA content between inbred strains of mice. The identification of these apparently common segmental polymorphisms suggests that these differences can contribute to genetic variability and pathologic susceptibility. 相似文献
103.
104.
Haematopoietic stem cells do not transdifferentiate into cardiac myocytes in myocardial infarcts 总被引:2,自引:0,他引:2
Murry CE Soonpaa MH Reinecke H Nakajima H Nakajima HO Rubart M Pasumarthi KB Virag JI Bartelmez SH Poppa V Bradford G Dowell JD Williams DA Field LJ 《Nature》2004,428(6983):664-668
The mammalian heart has a very limited regenerative capacity and, hence, heals by scar formation. Recent reports suggest that haematopoietic stem cells can transdifferentiate into unexpected phenotypes such as skeletal muscle, hepatocytes, epithelial cells, neurons, endothelial cells and cardiomyocytes, in response to tissue injury or placement in a new environment. Furthermore, transplanted human hearts contain myocytes derived from extra-cardiac progenitor cells, which may have originated from bone marrow. Although most studies suggest that transdifferentiation is extremely rare under physiological conditions, extensive regeneration of myocardial infarcts was reported recently after direct stem cell injection, prompting several clinical trials. Here, we used both cardiomyocyte-restricted and ubiquitously expressed reporter transgenes to track the fate of haematopoietic stem cells after 145 transplants into normal and injured adult mouse hearts. No transdifferentiation into cardiomyocytes was detectable when using these genetic techniques to follow cell fate, and stem-cell-engrafted hearts showed no overt increase in cardiomyocytes compared to sham-engrafted hearts. These results indicate that haematopoietic stem cells do not readily acquire a cardiac phenotype, and raise a cautionary note for clinical studies of infarct repair. 相似文献
105.
Disruption of the normal regulation of cell-cycle progression and division lies at the heart of the events leading to cancer. Complex networks of regulatory factors, the tumour microenvironment and stress signals, such as those resulting from damaged DNA, dictate whether cancer cells proliferate or die. Recent progress in understanding the molecular changes that underlie cancer development offer the prospect of specifically targeting malfunctioning molecules and pathways to achieve more effective and rational cancer therapy. 相似文献
106.
The herbivorous insects of tropical forests constitute some of the most diverse communities of living organisms. For this reason it has been difficult to discover the degree to which these communities are structured, and by what processes. Interspecific competition for resources does occur, but its contemporary importance is limited because most pairs of potentially competing insects feed on different host plants. An alternative way in which species can interact is through shared natural enemies, a process called apparent competition. Despite extensive theoretical discussion there are few field demonstrations of apparent competition, and none in hyper-diverse tropical communities. Here, we experimentally removed two species of herbivore from a community of leaf-mining insects in a tropical forest. We predicted that other species that share natural enemies with the two removed species would experience lower parasitism and have higher population densities in treatment compared with control sites. In both cases (on removal of a dipteran and a coleopteran leaf-miner species) we found significantly lower parasitism, and in one case (removal of the dipteran) we found significantly higher abundance a year after the manipulation. Our results suggest that apparent competition may be important in structuring tropical insect communities. 相似文献
107.
Matloubian M Lo CG Cinamon G Lesneski MJ Xu Y Brinkmann V Allende ML Proia RL Cyster JG 《Nature》2004,427(6972):355-360
Adaptive immunity depends on T-cell exit from the thymus and T and B cells travelling between secondary lymphoid organs to survey for antigens. After activation in lymphoid organs, T cells must again return to circulation to reach sites of infection; however, the mechanisms regulating lymphoid organ exit are unknown. An immunosuppressant drug, FTY720, inhibits lymphocyte emigration from lymphoid organs, and phosphorylated FTY720 binds and activates four of the five known sphingosine-1-phosphate (S1P) receptors. However, the role of S1P receptors in normal immune cell trafficking is unclear. Here we show that in mice whose haematopoietic cells lack a single S1P receptor (S1P1; also known as Edg1) there are no T cells in the periphery because mature T cells are unable to exit the thymus. Although B cells are present in peripheral lymphoid organs, they are severely deficient in blood and lymph. Adoptive cell transfer experiments establish an intrinsic requirement for S1P1 in T and B cells for lymphoid organ egress. Furthermore, S1P1-dependent chemotactic responsiveness is strongly upregulated in T-cell development before exit from the thymus, whereas S1P1 is downregulated during peripheral lymphocyte activation, and this is associated with retention in lymphoid organs. We find that FTY720 treatment downregulates S1P1, creating a temporary pharmacological S1P1-null state in lymphocytes, providing an explanation for the mechanism of FTY720-induced lymphocyte sequestration. These findings establish that S1P1 is essential for lymphocyte recirculation and that it regulates egress from both thymus and peripheral lymphoid organs. 相似文献
108.
109.
Brigitte Cambon de Lavalette Charles Tijus Christine Leproux Olivier Bauer 《Foundations of Science》2005,10(1):25-45
Taxonomy Based modeling was applied to describe drivers’ mental models of variable message signs (VMS’s) displayed on expressways.
Progress in road telematics has made it possible to introduce variable message signs (VMS’s). Sensors embedded in the carriageway
every 500m record certain variables (speed, flow rate, etc.) that are transformed in real time into “driving times” to a given
destination if road conditions do not change.
VMS systems are auto-regulative Man-Machine (AMMI) systems which incorporate a model of the user: if the traffic flow is too
high, then drivers should choose alternative routes. In so doing, the traffic flow should decrease. The model of the user
is based on suppositions such as: people do not like to waste time, they fully understand the displayed messages, they trust
the displayed values, they know of alternative routes. However, people also have a model of the way the system functions.
And if they do not believe the contents of the message, they will not act as expected.
We collected data through interviews with drivers using the critical incidents technique (Flanagan, 1985). Results show that
the mental models that drivers have of the way the VMS system works are various but not numerous and that most of them differ
from the“ideal expert” mental model. It is clear that users don’t have an adequate model of how the VMS system works and that
VMS planners have a model of user behaviour that does not correspond to the behaviour of the drivers we interviewed. Finally,
Taxonomy Based Modeling is discussed as a tool for mental model remediation. 相似文献
110.