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291.
Yuan Li David Lovett Qiao Zhang Srujana Neelam Ram?Anirudh Kuchibhotla Ruijun Zhu Gregg?G. Gundersen Tanmay?P. Lele Richard?B. Dickinson 《Biophysical journal》2015,109(4):670-686
The nucleus has a smooth, regular appearance in normal cells, and its shape is greatly altered in human pathologies. Yet, how the cell establishes nuclear shape is not well understood. We imaged the dynamics of nuclear shaping in NIH3T3 fibroblasts. Nuclei translated toward the substratum and began flattening during the early stages of cell spreading. Initially, nuclear height and width correlated with the degree of cell spreading, but over time, reached steady-state values even as the cell continued to spread. Actomyosin activity, actomyosin bundles, microtubules, and intermediate filaments, as well as the LINC complex, were all dispensable for nuclear flattening as long as the cell could spread. Inhibition of actin polymerization as well as myosin light chain kinase with the drug ML7 limited both the initial spreading of cells and flattening of nuclei, and for well-spread cells, inhibition of myosin-II ATPase with the drug blebbistatin decreased cell spreading with associated nuclear rounding. Together, these results show that cell spreading is necessary and sufficient to drive nuclear flattening under a wide range of conditions, including in the presence or absence of myosin activity. To explain this observation, we propose a computational model for nuclear and cell mechanics that shows how frictional transmission of stress from the moving cell boundaries to the nuclear surface shapes the nucleus during early cell spreading. Our results point to a surprisingly simple mechanical system in cells for establishing nuclear shapes. 相似文献
292.
The large amounts of dopamine accumulated by cells of Tetrahymena pyriformis strain NT-1 and secreted into their growth medium were found to depend primarily upon an extracellular, non-enzymatic conversion of tyrosine to L-dihydroxyphenylalanine (L-DOPA); L-DOPA was then rapidly taken into the ceils and transformed into dopamine enzymatically. Efforts to find physiologically significant dopamine binding sites on the cell surface or dopamine-sensitive adenylate cyclase activity were unsuccessful, suggesting that the catecholamine does not function in Tetrahymena as it does in higher animals. 相似文献
293.
Mary B. O'Neill Abigail Shockey Alex Zarley William Aylward Vegard Eldholm Andrew Kitchen Caitlin S. Pepperell 《Molecular ecology》2019,28(13):3241-3256
Mycobacterium tuberculosis (M.tb) is a globally distributed, obligate pathogen of humans that can be divided into seven clearly defined lineages. An emerging consensus places the origin and global dispersal of M.tb within the past 6,000 years: identifying how the ancestral clone of M.tb spread and differentiated within this timeframe is important for identifying the ecological drivers of the current pandemic. We used Bayesian phylogeographic inference to reconstruct the migratory history of M.tb in Africa and Eurasia and to investigate lineage specific patterns of spread from a geographically diverse sample of 552 M.tb genomes. Applying evolutionary rates inferred with ancient M.tb genome calibration, we estimated the timing of major events in the migratory history of the pathogen. Inferred timings contextualize M.tb dispersal within historical phenomena that altered patterns of connectivity throughout Africa and Eurasia: trans‐Indian Ocean trade in spices and other goods, the Silk Road and its predecessors, the expansion of the Roman Empire, and the European Age of Exploration. We found that Eastern Africa and Southeast Asia have been critical in the dispersal of M.tb. Our results further reveal that M.tb populations have grown through range expansion, as well as in situ, and delineate the independent evolutionary trajectories of bacterial subpopulations underlying the current pandemic. 相似文献
294.
Paulo Milet-Pinheiro Arthur Domingos-Melo João B. Olivera Nayara S.L. Albuquerque Ana Carolina G. Costa Sinzinando Albuquerque-Lima Marcelo F.R. Silva Daniela M.A.F. Navarro Artur C.D. Maia Lise-Lotte Gundersen Mario Schubert Stefan Dötterl Isabel C. Machado 《Current biology : CB》2021,31(4):860-868.e4
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