排序方式: 共有60条查询结果,搜索用时 281 毫秒
21.
22.
Astthor Gislason 《Hydrobiologia》2003,503(1-3):195-209
Abundance and seasonal vertical distribution of dominant zooplankters in the Irminger Sea was studied from data collected during four cruises between November 1996 and June 1997. In addition, egg production of Calanus finmarchicus was measured during winter, spring and summer 1996–2001. Five taxa constituted >95% of the copepod biomass, C. finmarchicus, Pareuchaeta norvegica, C. hyperboreus, Oithona spp. and Oncaea spp. A seasonal migration pattern was evident for C. finmarchicus, P. norvegica and Oithona spp.: from December to February, they inhabited the deeper layers, whereas, from April to June, they were most abundant in the upper layers. Oncaea spp. also stayed deep during winter and only a very limited part of the population rose to the surface during summer. C. hyperboreus remained deep from December to April, but had virtually disappeared in June. Reproduction of C. finmarchicus took place in May in the surface layers and was linked to the phytoplankton spring bloom. In contrast, reproduction of P. norvegica occurred at depth in February and was uncoupled with the spring bloom. C. hyperboreus did not reproduce in the Irminger Sea. Data on Oithona spp. and Oncaea spp. indicated that the former reproduced between April and June in the upper layers, whereas the latter reproduced year-round at depth. Thus, data on vertical distribution and seasonal stage composition suggested that the dominant copepods are separated, at least partly, at spatial and temporal scales with regard to overwintering and development. 相似文献
23.
Gudjonsson T Rønnov-Jessen L Villadsen R Bissell MJ Petersen OW 《Methods (San Diego, Calif.)》2003,30(3):247-255
The normal human breast comprises an inner layer of luminal epithelial cells and an outer layer of myoepithelial cells separated from the connective tissue stroma by an intact basement membrane. In breast cancer, tumor cells are in direct contact with the surrounding highly activated collagenous stroma, with little or no discernible myoepithelial fence from the original double-layered structure. To understand the evolution of these two scenarios, we took advantage of a three-dimensional hydrated collagen gel approach. The contribution of myoepithelial cells to normal morphogenesis was studied by ablation and rescue experiments, and genes regulated on tumor cell-fibroblast interaction were identified in a tumor environment assay. In normal breast morphogenesis, the ability to correctly polarize sialomucin to the luminal membrane of emerging acini was used as a criterion for apical polarity and functional differentiation. In the assay of breast neoplasia, the consequence of reciprocal tumor cell-fibroblast interaction was addressed morphologically as well as by a differential display approach. Normal breast epithelial cells were purified immunomagnetically and an established cell line, MCF-7, was used as a surrogate tumor cell. With regard to the importance of myoepithelial cells in normal breast epithelial morphogenesis, the collagen gel assay elucidated the following subtleties: In contrast to culturing in basement membrane gels, luminal epithelial cells when cultured alone made structures that were all inversely polarized. This aberrant polarity could be rescued by co-culture with myoepithelial cells. The molecular activity of myoepithelial cells responsible for correct morphogenesis was narrowed down to the laminin-1 component of the basement membrane. As for the consequence of interaction of tumor cells with connective tissue fibroblasts, the assay allowed us to identify a hitherto undescribed gene referred to as EPSTI1. The relevance of the assay-based identification of regulated genes was confirmed in a series of breast carcinomas in which EPSTI1 was highly upregulated compared with normal breast. Few if any of these observations would have been possible on two-dimensional tissue culture plastic. 相似文献
24.
Bahrke S Einarsson JM Gislason J Haebel S Letzel MC Peter-Katalinić J Peter MG 《Biomacromolecules》2002,3(4):696-704
Chitin/chitosan oligosaccharides composed of 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) and/or 2-amino-2-deoxy-D-glucopyranose (GlcN) were prepared by chemical degradation of chitin or chitosan and separated by gel permeation chromatography. Oligosaccharides obtained after enzymatic hydrolysis of chitosan [F(A) 0.19] with a fungal chitinase were derivatized by reductive amination with 2-aminoacridone and sequenced by matrix-assisted laser desorption ionization time-of-flight postsource decay (PSD) mass spectrometry (MS). The sequence of a trimer, D1A2, was established as D-A-A. The composition of a hexamer D3A3 was ca. 65% D-A-D-D-A-A and 35% D-D-A-D-A-A. The PSD MS of a nonamer D5A4-amac revealed four isobaric species D-X-Y-D-X-Y-D-A-A, where A is GlcNAc, D is GlcN, and X and Y (X not equal Y) are mutually either D or A. This structure motif was also observed in a dodecamer D7A5 which was composed of eight isobaric sequences of the general formula (D-X-Y)(3)-D-A-A. 相似文献
25.
Nicholas Carlson Kristine Hommel Jonas Bjerring Olesen Anne-Merete Soja Tina Vilsb?ll Anne-Lise Kamper Christian Torp-Pedersen Gunnar Gislason 《PloS one》2016,11(2)
Introduction
Dialysis-requiring acute kidney injury is a severe illness associated with poor prognosis. However, information pertaining to incidence rates and prevalence of risk factors remains limited in spite of increasing focus. We evaluate time trends of incidence rates and changing patterns in prevalence of comorbidities, concurrent medication, and other risk factors in nationwide retrospective cohort study.Materials and Methods
All patients with dialysis-requiring acute kidney injury were identified between January 1st 2000 and December 31st 2012. By cross-referencing data from national administrative registries, the association of changing patterns in dialysis treatment, comorbidity, concurrent medication and demographics with incidence of dialysis-requiring acute kidney injury was evaluated.Results
A total of 18,561 adult patients with dialysis-requiring AKI were identified between 2000 and 2012. Crude incidence rate of dialysis-requiring AKI increased from 143 per million (95% confidence interval, 137–144) in 2000 to 366 per million (357–375) in 2006, and remained stable hereafter. Notably, incidence of continuous veno-venous hemodialysis (CRRT) and use of acute renal replacement therapy in elderly >75 years increased substantially from 23 per million (20–26) and 328 per million (300–355) in 2000, to 213 per million (206–220) and 1124 per million (1076–1172) in 2012, respectively. Simultaneously, patient characteristics and demographics shifted towards increased age and comorbidity.Conclusions
Although growth in crude incidence rate of dialysis-requiring AKI stabilized in 2006, continuous growth in use of CRRT, and acute renal replacement therapy of elderly patients >75 years, was observed. Our results indicate an underlying shift in clinical paradigm, as opposed to unadulterated growth in incidence of dialysis-requiring AKI. 相似文献26.
Epithelial progenitor cell lines as models of normal breast morphogenesis and neoplasia 总被引:8,自引:0,他引:8
Ole William Petersen Thorarinn Gudjonsson‡ René Villadsen Mina J. Bissell§ Lone Rønnov-Jessen† 《Cell proliferation》2003,36(S1):33-44
Abstract. The majority of human breast carcinomas exhibit luminal characteristics and as such, are most probably derived from progenitor cells within the luminal epithelial compartment. This has been subdivided recently into at least three luminal subtypes based on gene expression patterns. The value of knowing the cellular origin of individual tumours is clear and should aid in designing effective therapies. To do this, however, we need strategies aimed at defining the nature of stem and progenitor cell populations in the normal breast. In this review, we will discuss our technical approach for delineating the origin of the epithelial cell types. A major step forward was the purification of each cell type by the application of immunomagnetic cell sorting based on expression of lineage-specific surface antigens. We then developed chemically defined media that could support either the luminal epithelial or the myoepithelial cell phenotype in primary cultures. Having succeeded in continuous propagation presumably without loss of markers, we could show that a subset of the luminal epithelial cells could convert to myoepithelial cells, signifying the possible existence of a progenitor cell population. By combining the information on marker expression and in situ localization with immunomagnetic sorting and subsequent immortalization, we have identifed and isolated a cytokeratin 19-positive suprabasal putative precursor cell in the luminal epithelial compartment and established representative cell lines. This suprabasal-derived epithelial cell line is able to generate both itself and differentiated luminal epithelial and myoepithelial cells, and in addition, is able to form elaborate terminal duct lobular unit (TDLU)-like structures within a reconstituted basement membrane. As more than 90% of breast cancers arise in TDLUs and more than 90% are also cytokeratin 19-positive, we suggest that this cell population contains a breast-cancer progenitor. 相似文献
27.
Rhodothermus marinus: physiology and molecular biology 总被引:2,自引:0,他引:2
Bjornsdottir SH Blondal T Hreggvidsson GO Eggertsson G Petursdottir S Hjorleifsdottir S Thorbjarnardottir SH Kristjansson JK 《Extremophiles : life under extreme conditions》2006,10(1):1-16
Rhodothermus marinus has been the subject of many studies in recent years. It is a thermohalophilic bacterium and is the only validly described species in the genus Rhodothermus. It is not closely related to other well-known thermophiles and is the only thermophile within the family Crenotrichaceae. R. marinus has been isolated from several similar but distantly located geothermal habitats, many of which are subject to large fluctuations in environmental conditions. This presumably affects the physiology of R. marinus. Many of its enzymes show optimum activity at temperatures considerably higher than 65°C, the optimum for growth, and some are active over a broad temperature range. Studies have found distinguishing components in the R. marinus electron transport chain as well as in its pool of intracellular solutes, which accumulate during osmotic stress. The species hosts both bacteriophages and plasmids and a functional intein has been isolated from its chromosome. Despite these interesting features and its unknown genetics, interest in R. marinus has been mostly stimulated by its thermostable enzymes, particularly polysaccharide hydrolysing enzymes and enzymes of DNA synthesis which may be useful in industry and in the laboratory. R. marinus has not been amenable to genetic analysis until recently when a system for gene transfer was established. Here, we review the current literature on R. marinus. 相似文献
28.
The functional response of whiting (Merlangius merlangus L.) to clupeid and gadoid prey was determined from estimates of food intake and prey density at five locations in the North Sea. The intake of most prey types was well described by a type II (decelerating) response, although in some cases a type III (sigmoid) response provided a slightly better fit. Though a saturation level was reached for all types of fish prey, none of the levels corresponded to the maximum digestive capacity of the predator. This was not caused by ingestion of other prey as the amount of other food and fish prey ingested were not negatively correlated. An investigation of the occurrence of fresh fish in the stomachs revealed that fish was ingested almost exclusively during dawn and dusk and the lack of negative correlation between the intake of fish and other prey may thus be a result of the limited time in which fish prey was vulnerable to predation. No aggregative response of the predators was detected towards any of the prey and catches of prey and predators were slightly negatively correlated. There was evidence of an increase in mortality with density at low clupeid densities, but mortality decreased to virtually zero at high densities. Whiting seem therefore unlikely to impose a regulatory effect on their fish prey outside a narrow range of prey densities. 相似文献
29.
30.
Maurizia Rossana Brunetto Daniela Cavallone Filippo Oliveri Francesco Moriconi Piero Colombatto Barbara Coco Pietro Ciccorossi Carlotta Rastelli Veronica Romagnoli Beatrice Cherubini Maria Wrang Teilum Thorarinn Blondal Ferruccio Bonino 《PloS one》2014,9(10)