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排序方式: 共有131条查询结果,搜索用时 15 毫秒
41.
Rodal AA Blunk AD Akbergenova Y Jorquera RA Buhl LK Littleton JT 《The Journal of cell biology》2011,193(1):201-217
Structural remodeling of synapses in response to growth signals leads to long-lasting alterations in neuronal function in many systems. Synaptic growth factor receptors alter their signaling properties during transit through the endocytic pathway, but the mechanisms controlling cargo traffic between endocytic compartments remain unclear. Nwk (Nervous Wreck) is a presynaptic F-BAR/SH3 protein that regulates synaptic growth signaling in Drosophila melanogaster. In this paper, we show that Nwk acts through a physical interaction with sorting nexin 16 (SNX16). SNX16 promotes synaptic growth signaling by activated bone morphogenic protein receptors, and live imaging in neurons reveals that SNX16-positive early endosomes undergo transient interactions with Nwk-containing recycling endosomes. We identify an alternative signal termination pathway in the absence of Snx16 that is controlled by endosomal sorting complex required for transport (ESCRT)-mediated internalization of receptors into the endosomal lumen. Our results define a presynaptic trafficking pathway mediated by SNX16, NWK, and the ESCRT complex that functions to control synaptic growth signaling at the interface between endosomal compartments. 相似文献
42.
Helicobacter pylori inhibits gastric cell cycle progression 总被引:3,自引:0,他引:3
Ahmed A Smoot D Littleton G Tackey R Walters CS Kashanchi F Allen CR Ashktorab H 《Microbes and infection / Institut Pasteur》2000,2(10):1159-1169
Helicobacter pylori infection of the gastric mucosa is associated with changes in gastric epithelial cell proliferation. In vitro studies have shown that exposure to H. pylori inhibits proliferation of gastric cells. This study sought to investigate the cell cycle progression of gastric epithelial cell lines in the presence and absence of H. pylori. Unsynchronized and synchronized gastric epithelial cell lines AGS and KatoIII were exposed to H. pylori over a 24-h period. Cell cycle progression was determined by flow cytometry using propidium iodide (PI), and by analysis of cyclin E, p21, and p53 protein expression using Western blots. In the absence of H. pylori 40, 45, and 15% of unsynchronized AGS cells were in G(0)-G(1), S, and G(2)-M phases, respectively, by flow cytometry analysis. When AGS cells were cultured in the presence of H. pylori, the S phase decreased 10% and the G(0)-G(1) phase increased 17% after 24 h compared with the controls. KatoIII cells, which have a deleted p53 gene, showed little or no response to H. pylori. When G1/S synchronized AGS cells were incubated with media containing H. pylori, the G(1) phase increased significantly (25%, P < 0.05) compared with controls after 24 h. In contrast, the control cells were able to pass through S phase. The inhibitory effects of H. pylori on the cell cycle of AGS cells were associated with a significant increase in p53 and p21 expression after 24 h. The expression of cyclin E was downregulated in AGS cells following exposure of AGS cells to H. pylori for 24 h. This study shows that H. pylori-induced growth inhibition in vitro is predominantly at the G(0)-G(1) checkpoint. Our results suggest that p53 may be important in H. pylori-induced cell cycle arrest. These results support a role for cyclin-dependent kinase inhibitors in the G(1) cell cycle arrest exerted by H. pylori and its involvement in changing the regulatory proteins, p53, p21, and cyclin E in the cell cycle. 相似文献
43.
David?N. Herrmann Rita Horvath Janet?E. Sowden Michael Gonzalez Avencia Sanchez-Mejias Zhuo Guan Roger?G. Whittaker Jorge?L. Almodovar Maria Lane Boglarka Bansagi Angela Pyle Veronika Boczonadi Hanns Lochmüller Helen Griffin Patrick?F. Chinnery Thomas?E. Lloyd J.?Troy Littleton Stephan Zuchner 《American journal of human genetics》2014,95(4):472
44.
R Podstawski DJ Choszcz S Konopka J Klimczak M Starczewski 《Biology of sport / Institute of Sport》2014,31(4):315-321
The aim of the study was to evaluate anthropometric characteristics as determinants of 500 m rowing ergometer performance in physically inactive collegiate females. In this cross-sectional study, which included 196 collegiate females aged 19-23 years not participating in regular physical activities, body mass (BM), body height (BH), length of upper limbs (LA), length of lower limbs (LL), body mass index (BMI), slenderness index (SI), and the Choszcz-Podstawski index (CPI) were measured and a stepwise multiple regression analysis was performed. Participants performed 500 m maximal effort on a Concept II rowing ergometer. BM, BH, LA, LL, and the BMI, SI and CPI indices were found to be statistically significant determinants of 500 m performance. The best results (T) were achieved by females whose BH ranged from 170 to 180 cm, with LA and LL ranging from 75 to 80 cm and 85 to 90 cm, respectively. The best fitting statistical model was identified as: T = 11.6793 LR – 0.1130 LR2 – 0.0589 LN2 + 29.2157 CPI2 + 0.1370 LR·LN - 2.6926 LR·CPI – 211.7796. This study supports a need for additional studies focusing on understanding the importance of anthropometric differences in rowing ergometer performance, which could lead to establishing a better quality reference for evaluation of cardiorespiratory fitness tested using a rowing ergometer in collegiate females. 相似文献
45.
46.
Evolution at the tip and base of the X chromosome in an African population of Drosophila melanogaster 总被引:1,自引:0,他引:1
Hitchhiking effects of advantageous mutations have been invoked to explain
reduced polymorphism in regions of low crossing-over in Drosophila. Besides
reducing DNA heterozygosity, hitchhiking effects should produce strong
linkage disequilibrium and a frequency spectrum skewed toward an excess of
rare polymorphisms (compared to the neutral expectation). We measured DNA
polymorphism in a Zimbabwe population of D. melanogaster at three loci,
yellow, achaete, and suppressor of forked, located in regions of reduced
crossing-over. Similar to previously published surveys of these genomic
regions in other populations, we observed low levels of nucleotide
variability. However, the frequency spectrum was compatible with a neutral
model, and there was abundant evidence for recombination in the history of
the yellow and ac genes. Thus, some aspects of the data cannot be accounted
for by a simple hitchhiking model. An alternative hypothesis, background
selection, might be compatible with the observed patterns of linkage
disequilibrium and the frequency spectrum. However, this model cannot
account for the observed reduction in nucleotide heterozygosity. Thus,
there is currently no satisfactory theoretical model for the data from the
tip and base of the X chromosome in D. melanogaster.
相似文献
47.
Oligogalacturonic acids (OGAs), derived from plant cell wall pectin, have
been implicated in a number of signal transduction pathways involved in
growth, development and defense responses of higher plants. This study
investigates the size range of OGAs capable of inducing ethylene synthesis
in tomato plants, and demonstrates that in contrast with many other
effects, only short chain OGAs are active. Oligomers across a range of DP
from 2-15 were separated and purified to homogeneity by QAE-Sephadex anion
exchange chromatography using a novel elution system. The OGAs were applied
to tomato plants and assayed for their ability to induce ethylene gas
release and changes in steady state levels of mRNA encoding the ethylene
forming enzyme aminocyclopropane-1-carboxylic acid oxidase (ACO). The study
demonstrated that only OGAs in the size range of DP4-6 were active both in
eliciting ACO expression and in the production of ethylene.
相似文献
48.
A change in twist of actin provides the force for the extension of the acrosomal process in limulus sperm: the false-discharge reaction 总被引:6,自引:5,他引:1 下载免费PDF全文
One of the most spectacular motions is the generation of the acrosomal process in the limulus sperm. On contact with the egg, the sperm generates a 60-mum-long process that literally drills its way through the jelly surrounding the egg. This irresversible reaction takes only a few seconds. We suggested earlier that this motion is driven by a change in twist of the actin filaments comprising the acrosomal process. In this paper we analyze the so-called false discharge, a reversible reaction, in which the acrosomal filament bundle extends laterally from the base of the sperm and not anteriorly from the apex. Unlike the true discharge, which is straight, the false discharge is helical. Before extension, the filament bundle is coiled about the base of the sperm. In the coil, the bundle is not smoothly bent but consists of arms (straight segments) and elbows (corners) so that the coil looks like a 14-sided polygon. The extension of the false discharge works as follows: starting at the base of the bundle, the filaments change their twist which concomitantly changes the orientations of the elbows relative to each other; that is, in the coil, the elbows all like in a common plane, but after the change in twist, the plane of each elbow is rotated to be perpendicular to that of its neighbors. This change transforms the bundle from a compact coil into an extended left- handed helix. Because the basal end of the bundle is unconstrained, the extension is lateral. The true discharge works the same way but starts at the apical end of the bundle. The apical end, however, is constrained by its passage through the nuclear canal, which directs the extention anteriorly. Unlike the false discharge, during the true discharge the elbows are melted out, making the reaction irreversible. This study shows that rapid movement can be regenerated by actin without myosin and gives us insight into the molecular mechanism. 相似文献
49.
Using the endogenous spleen colony assay method of Till & McCulloch (1963), the numbers of haemopoietic stem cells present in the bone marrow in the tails of mice were estimated under different environmental temperatures. Compared to animals kept at 22–26°C, mice transferred to and kept at 36.5°C showed a doubling of colony-forming units in the tail in 1–4 weeks. Exposing them to 8°C caused a significant depopulation to approximately one-third in 3–4 weeks. By transferring the mice from one temperature extreme to another these changes could be reversed. Tail marrow depleted of viable stem cells by X-irradiation was repopulated within approximately 3 weeks in animals kept at room temperature or above but this process was inhibited in the cold. 相似文献
50.
Littleton J 《American journal of primatology》2005,67(3):281-298
There has been a captive Pan troglodytes colony at Taronga Park Zoo in Sydney, Australia, since the mid-1930s. Demographic data on these animals were first analyzed in 1986; however, further information collected for 15 years since then is now available. The reproductive histories of 33 females in the colony have been recorded, and these data form the largest collection of captive chimpanzee data from a setting that has involved natural breeding conditions since the mid-1960s. These data were analyzed in conjunction with data from wild populations to establish the degree of variability present within chimpanzee reproductive parameters, and to identify which distinctive life history characteristics persist in well-provisioned, natural-fertility populations. The age at first birth for the chimpanzee females is 9.8 yr on average (n=16), which is 1-4.8 yr earlier than the average for wild populations. In line with this accelerated reproduction, birth intervals are also significantly shorter than those in noncaptive chimpanzee populations. The median birth interval for all surviving infants (based on a Kaplan-Meier survival analysis) is 49 months (n=43) compared to 62+ months for wild groups. At the same time, infant mortality remains high. The data confirm distinctive features of the life history of common chimpanzees, including later maturation, long birth intervals, a relatively invariant fertility schedule, and high juvenile mortality. However, aspects of both fertility and mortality are significantly related to social circumstances, indicating that in common chimpanzees, as in humans, life history characters may represent ecological and social adaptations rather than species-fixed characteristics. 相似文献