排序方式: 共有55条查询结果,搜索用时 281 毫秒
41.
Participation of plasma membrane proteins in the formation of tight junction by cultured epithelial cells
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Measurements of the transepithelial electrical resistance correlated with freeze-fracture observations have been used to study the process of tight junction formation under various experimental conditions in monolayers of the canine kidney epithelial cell line MDCK. Cells derived from previously confluent cultures and plated immediately after trypsin- EDTA dissociation develop a resistance that reaches its maximum value of several hundred ohms-cm(2) after approximately 24 h and falls to a steady-state value of 80-150 ohms- cm(2) by 48 h. The rise in resistance and the development of tight junctions can be completely and reversibly prevented by the addition of 10 μg/ml cycloheximide at the time of plating, but not when this inhibitor is added more than 10 h after planting. Thus tight junction formation consists of separable synthetic and assembly phases. These two phases can also be dissociated and the requirement for protein synthesis after plating eliminated if, following trypsinization, the cells are maintained in spinner culture for 24 h before plating. The requirement for protein synthesis is restored, however, if cells maintained in spinner culture are treated with trypsin before plating. Actinomycin D prevents development of resistance only in monolayers formed from cells derived from sparse rather than confluent cultures, but new mRNA synthesis is not required if cells obtained from sparse cultures are maintained for 24 h in spinner culture before plating. Once a steady-state resistance has been reached, its maintenance does not require either mRNA or protein synthesis; in fact, inhibition of protein synthesis causes a rise in the resistance over a 30-h period. Following treatments that disrupt the junctions in steady- state monolayers recovery of resistance also does not require protein synthesis. These observations suggest that proteins are involved in tight junction formation. Such proteins, which do not turn over rapidly under steady-state conditions, are destroyed by trypsinization and can be resynthesized in the absence of stable cell-cell or cell-substratum contact. Messenger RNA coding for proteins involved in tight junction formation is stable except when cells are sparsely plated, and can also be synthesized without intercellular contacts or cell-substratum attachment. 相似文献
42.
A comparison of two methods for constructing evolutionary distances from a weighted contribution of transition and transversion differences 总被引:3,自引:3,他引:0
Since the initial work of Jukes and Cantor (1969), a number of procedures
have been developed to estimate the expected number of nucleotide
substitutions corresponding to a given observed level of nucleotide
differentiation assuming particular evolutionary models. Unlike the
proportion of different sites, the expected number of substitutions that
would have occurred grows linearly with time and therefore has had great
appeal as an evolutionary distance. Recently, however, a number of authors
have tried to develop improved statistical approaches for generating and
evaluating evolutionary distances (Schoniger and von Haeseler 1993;
Goldstein and Polock 1994; Tajima and Takezaki 1994). These studies clearly
show that the estimated number of nucleotide substitutions is generally not
the best estimator for use in reconstruction of phylogenetic relationships.
The reason for this is that there is often a large error associated with
the estimation of this number. Therefore, even though its expectation is
correct (i.e., on average the expected number of substitutions is
proportional to time- -but see Tajima 1993), it is not expected to be as
useful as estimators designed to have a lower variance.
相似文献
43.
44.
WJ Richardson DD van der Voort E Wilson JE Moore Jr. 《Molecular & cellular biomechanics : MCB》2013,10(3):245-265
Non-uniform stress and strain fields are prevalent in many tissues in vivo, and often exacerbated by disease or injury. These mechanical gradients potentially play a role in contributing to pathological conditions, presenting a need for experimental tools to allow investigation of cell behavior within non-uniformly stimulated environments. Herein, we employ two in vitro cell-stretching devices (one previously published; one newly presented) capable of subjecting cells to cyclic, non-uniform stretches upon the surface of either a circular elastomeric membrane or a cylindrical PDMS tube. After 24 hours of cyclic stretch, 10T1/2 cells on both devices showed marked changes in long-axis orientation, with tendencies to align parallel to the direction of minimal deformation. The degree of this response varied depending on location within the stretch gradients. These results demonstrated the feasibility of conducting cell mechanobiology investigations with the two novel devices, while also highlighting the experimental capabilities of non-uniform mechanical environments for these types of studies. Such capabilities include robust data collection for developing mechanobiological dose-response curves, signal threshold identification, and potential spatial targeting for drug delivery. 相似文献
45.
Aline S. M. Cesar Luciana C. A. Regitano James E. Koltes Eric R. Fritz-Waters Dante P. D. Lanna Gustavo Gasparin Gerson B. Mour?o Priscila S. N. Oliveira James M. Reecy Luiz L. Coutinho 《PloS one》2015,10(6)
Intramuscular fat (IMF) content is related to insulin resistance, which is an important prediction factor for disorders, such as cardiovascular disease, obesity and type 2 diabetes in human. At the same time, it is an economically important trait, which influences the sensorial and nutritional value of meat. The deposition of IMF is influenced by many factors such as sex, age, nutrition, and genetics. In this study Nellore steers (Bos taurus indicus subspecies) were used to better understand the molecular mechanisms involved in IMF content. This was accomplished by identifying differentially expressed genes (DEG), biological pathways and putative regulatory factors. Animals included in this study had extreme genomic estimated breeding value (GEBV) for IMF. RNA-seq analysis, gene set enrichment analysis (GSEA) and co-expression network methods, such as partial correlation coefficient with information theory (PCIT), regulatory impact factor (RIF) and phenotypic impact factor (PIF) were utilized to better understand intramuscular adipogenesis. A total of 16,101 genes were analyzed in both groups (high (H) and low (L) GEBV) and 77 DEG (FDR 10%) were identified between the two groups. Pathway Studio software identified 13 significantly over-represented pathways, functional classes and small molecule signaling pathways within the DEG list. PCIT analyses identified genes with a difference in the number of gene-gene correlations between H and L group and detected putative regulatory factors involved in IMF content. Candidate genes identified by PCIT include: ANKRD26, HOXC5 and PPAPDC2. RIF and PIF analyses identified several candidate genes: GLI2 and IGF2 (RIF1), MPC1 and UBL5 (RIF2) and a host of small RNAs, including miR-1281 (PIF). These findings contribute to a better understanding of the molecular mechanisms that underlie fat content and energy balance in muscle and provide important information for the production of healthier beef for human consumption. 相似文献
46.
47.
48.
The presence of the diagnostic character of the genus Paraleucilla (Amphoriscidae,Calcarea, Porifera) may depend on the volume and body wall thickness of the sponges
下载免费PDF全文
![点击此处可从《Invertebrate Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The main difference between the sponge genera Leucilla and Paraleucilla (Porifera, Calcarea, Amphoriscidae) is the presence of a disorganized zone (DZ) in the inner region of the skeleton of the latter genus. However, it has been repeatedly observed that specimens from different species of Paraleucilla lack this feature. It is assumed that the size of the sponge may have an effect on the presence or the absence of the DZ, but no investigation of this morphological variation has previously tested this hypothesis. Here, we examined this assumption and described the frequency with which the DZ is absent from individuals of Paraleucilla magna. We also investigated possible drivers of the observed variation using generalized linear models to evaluate whether the month of the year, rainfall, reproductive activity, volume, and body wall thickness could influence the presence or the absence of the DZ. The DZ was absent from 46.5% of the analyzed individuals, indicating that it may be misleading to use this trait to identify the genera Leucilla and Paraleucilla. The presence of the DZ in P. magna is influenced negatively by volume and positively by body wall thickness of the individuals. Our results confirm the previous assumptions for the family Amphoriscidae and highlight problems with the current classification of Calcarea. A discussion of the validity of some morphological characters and the importance of analyzing their variation is provided. 相似文献
49.
The Magnitude of Global Marine Species Diversity 总被引:1,自引:0,他引:1
Ward Appeltans Shane T. Ahyong Gary Anderson Martin V. Angel Tom Artois Nicolas Bailly Roger Bamber Anthony Barber Ilse Bartsch Annalisa Berta Magdalena Błażewicz-Paszkowycz Phil Bock Geoff Boxshall Christopher B. Boyko Simone Nunes Brandão Rod A. Bray Niel L. Bruce Stephen D. Cairns Tin-Yam Chan Lanna Cheng Mark J. Costello 《Current biology : CB》2012,22(23):2189-2202
50.