03/06/07 -- Like our body every cell has a skeleton that provides it with a shape, confers rigidity and protects its fragile inner workings. The cytoskeleton is built of long protein filaments that assemble into networks whose overall architecture and fine detail can only be revealed with high resolution electron microscopy images. Researchers at the European Molecular Biology Laboratory [EMBL] and the University of Colorado have now obtained the first 3D visualisation of a complete eukaryotic cell at a resolution high enough to resolve the cytoskeleton's precise architectural plan in fission yeast. The image of this unicellular organism will be published in this week's issue of the journal Developmental Cell and reveals remarkable insights into the fine structure of the cytoskeleton as well as its interactions with other parts of the cell.
A key component of the cytoskeleton are long, tube-like filaments called microtubules. They are dynamic structures built of constantly growing and shrinking rows of elementary proteins called tubulins. To increase their rigidity, microtubules associate in bundles and interact with stabilizing proteins in complex networks, which are essential for many cellular processes such as polar growth.
"To really understand the architecture of the cytoskeleton you have to see the entire cell in three dimensions," says Claude Antony, whose team carried out the research at EMBL, "but at the same time you need a very good resolution to be able to investigate its structural details. It is impossible to obtain such detailed images of a eukaryotic cell with normal microscopes."
To bridge the gap between global overview and structural detail Antony's team collaborated with yeast and electron microscopy expert Richard McIntosh at the University of Colorado. Using a technique called electron tomography, Johanna Höög, PhD student Antony's lab, took pictures of sequential sections of a yeast cell from many different angles through an electron microscope and combined these snapshots into a 3D reconstruction on the computer. A similar principle is used to generate brain scans.
For the first time they could see directly what previous studies in fission yeast only suggested. In times when a cell is not dividing, a microtubule bundle consists of 4-5 individual filaments that are physically connected with each other via minute bridges likely formed by proteins. In the networks created through this crosslinking the orientation of microtubules is crucial. The filaments are polar structures, their two ends grow and shrink at different rates. The study created a precise map indicating the location of all growing and shrinking microtubule ends in the cell.
The images also shed light on other important functions of microtubules, revealing that the cytoskeleton determines the correct positioning of mitochondria, the energy-producing organelles, throughout the cell.
"Our 3D image of fission yeast can serve as a reference map of the cell for all biologists interested in its architecture," says Johanna Höög. "You can extract information about all sorts of cellular structures and processes from it or use it to place findings into the spatial context of the cell."
Yeast is one of the most commonly used model organisms in biology. It has many similarities with higher eukaryotes, including multicellular organisms. Many of the insights gained into its cellular organisation are likely to apply also to mammals. In mammalian nerve cells, for example, microtubule bundles similar to those observed in yeast are essential for the transmission of the signal from cell to cell.
Source: European Molecular Biology Laboratory
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03/06/07 --象我们人体一样，每一个细胞都有一个骨架来维持其形状，参与提供刚性和保护细胞内部脆弱的结构。细胞骨架由一些长丝状蛋白组装成网络，这种网络的总体建筑结构和精细之处只能通过高分辨力电子显微镜来观察揭示。欧洲分子生物学实验室（EMBL）和 Colorado大学的研究人员现在已经 得到完整真核细胞的第一张三维照片，其分辨力足够完成旨在显示裂殖酵母精确结构的计划。将发表在本周Developmental Cell杂志上关于这种单细胞生物的图片，深入揭示了细胞骨架的精细结构和细胞骨架与细胞内其它部分的相互作用。
作者:admin@医学,生命科学 2011-02-18 05:14