313 research outputs found
Kinetic Monte Carlo simulations of oscillatory shape evolution for electromigration-driven islands
The shape evolution of two-dimensional islands under electromigration-driven
periphery diffusion is studied by kinetic Monte Carlo (KMC) simulations and
continuum theory. The energetics of the KMC model is adapted to the Cu(100)
surface, and the continuum model is matched to the KMC model by a suitably
parametrized choice of the orientation-dependent step stiffness and step atom
mobility. At 700 K shape oscillations predicted by continuum theory are
quantitatively verified by the KMC simulations, while at 500 K qualitative
differences between the two modeling approaches are found.Comment: 7 pages, 6 figure
The separation and sequencing of permethylated peptides by mass spectrometry directly coupled to gas-liquid chromatography
Human embryonic stem cells passaged using enzymatic methods retain a normal karyotype and express CD30
Human embryonic stem cells (hESCs) are thought to be susceptible to chromosomal rearrangements as a consequence of single cell dissociation. Compared in this study are two methods of dissociation that do not generate single cell suspensions (collagenase and EDTA) with an enzymatic procedure using trypsin combined with the calcium-specific chelator EGTA (TEG), that does generate a single cell suspension, over 10 passages. Cells passaged by single cell dissociation using TEG retained a normal karyotype. However, cells passaged using EDTA, without trypsin, acquired an isochromosome p7 in three replicates of one experiment. In all of the TEG, collagenase and EDTA-treated cultures, cells retained consistent telomere length and potentiality, demonstrating that single cell dissociation can be used to maintain karyotypically and phenotypically normal hESCs. However, competitive genomic hybridization revealed that subkaryotypic deletions and amplifications could accumulate over time, reinforcing that present culture regimes remain suboptimal. In all cultures the cell surface marker CD30, reportedly expressed on embryonal carcinoma but not karyoptically normal ESCs, was expressed on hESCs with both normal and abnormal karyotype, but was upregulated on the latter. Ā© 2008 Mary Ann Liebert, Inc
Bioluminescence imaging of human embryonic stem cells transplanted in vivo in murine and chick models
Research into the behavior, efficacy, and biosafety of stem cells with a view to clinical transplantation requires the development of noninvasive methods for in vivo imaging of cells transplanted into animal models. This is particularly relevant for human embryonic stem cells (hESCs), because transplantation of undifferentiated hESCs leads to tumor formation. The present study aimed to monitor hESCs in real time when injected in vivo. hESCs were stably transfected to express luciferase, and luciferase expression was clearly detected in the undifferentiated and differentiated state. When transfected hESCs were injected into chick embryos, bioluminescence could be detected both ex and in ovo. In the SCID mouse model, undifferentiated hESCs were detectable after injection either into the muscle layer of the peritoneum or the kidney capsule. Tumors became detectable between days 10-30, with approximately a 3 log increase in the luminescence signal by day 75. The growth phase occurred earlier in the kidney capsule and then reached a plateau, whilst tumors in the peritoneal wall grew steadily throughout the period analysed. These results show the widespread utility of bioluminescent for in vivo imaging of hESCs in a variety of model systems for preclinical research into regenerative medicine and cancer biology. Ā© Copyright 2009, Mary Ann Liebert, Inc
Studies on the subunit structure and amino acid sequence of triose phosphate isomerase from chicken breast muscle
The species composition of Antarctic phytoplankton interpreted in terms of Tilman's competition theory
An attempt was made, to test for the impact of resource competition on Antarctic marine phytoplankton. According to theory, species composition near competitive equilibrium should be determined by the ratios of limiting resources. Enrichment bioassays identified silicon and nitrogen as limiting nutrients for some of the most important phytoplankton species during early austral summer in the region near the Antarctic Peninsula. Together with the generally acknowledged limiting resource light, this gave three meaningful ratios of essential resources (Si:N, Si:light, N:light) and one ratio of substitutable resources (NO sub(3):NH sub(4)). Phytoplankton species assemblages were found to be well separated by the ratios of the essential resources and by mixing depth
Changes in seabird species abundance near South Georgia during a period of rapid change in sea surface temperature
A semiāautomated line tracing technique for monitoring ice margins in Antarctic images
PIPKIĪ³ Regulates Focal Adhesion Dynamics and Colon Cancer Cell Invasion
Focal adhesion assembly and disassembly are essential for cell migration and cancer invasion, but the detailed molecular mechanisms regulating these processes remain to be elucidated. Phosphatidylinositol phosphate kinase type IĪ³ (PIPKIĪ³) binds talin and is required for focal adhesion formation in EGF-stimulated cells, but its role in regulating focal adhesion dynamics and cancer invasion is poorly understood. We show here that overexpression of PIPKIĪ³ promoted focal adhesion formation, whereas cells expressing either PIPKIĪ³K188,200R or PIPKIĪ³D316K, two kinase-dead mutants, had much fewer focal adhesions than those expressing WT PIPKIĪ³ in CHO-K1 cells and HCT116 colon cancer cells. Furthermore, overexpression of PIPKIĪ³, but not PIPKIĪ³K188,200R, resulted in an increase in both focal adhesion assembly and disassembly rates. Depletion of PIPKIĪ³ by using shRNA strongly inhibited formation of focal adhesions in HCT116 cells. Overexpression of PIPKIĪ³K188,200R or depletion of PIPKIĪ³ reduced the strength of HCT116 cell adhesion to fibronection and inhibited the invasive capacities of HCT116 cells. PIPKIĪ³ depletion reduced PIP2 levels to ā¼40% of control and PIP3 to undetectable levels, and inhibited vinculin localizing to focal adhesions. Taken together, PIPKIĪ³ positively regulates focal adhesion dynamics and cancer invasion, most probably through PIP2-mediated vinculin activation
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