Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston, 6431 Fannin Street, Houston, TX 77030, USA.
Curr Biol. 2013 Jul 8;23(13):R553-6. doi: 10.1016/j.cub.2013.05.024.
A mother cell giving rise to offspring usually needs to choose the site of cytokinesis carefully, as this will determine the size and shape of the daughter cells. Rod-shaped bacteria that divide by binary fission, such as Escherichia coli, often mark their cell division sites at their cell midpoint so that daughter cells are roughly equivalent in size and shape. So how does E. coli know where its middle is? Its cell poles are defined by the previous cell division, but, because E. coli grows by incorporating new cell wall and membrane uniformly along its length, the future cell division site at mid-cell is newly made and has no known pre-existing markers. One way to select the new mid-cell site would be to measure the distance from the two opposing cell poles, using a system that could recognize markers at those poles and define the spot furthest from both markers. This would require that both polar markers act negatively on cell division at equivalent intensities. The result would be a concentration gradient, with the lowest concentration of the negative regulator at the cell midpoint, the greatest distance from both cell poles. It turns out that E. coli and some other rod-shaped bacteria select their cell midpoint using such a negatively acting morphogen gradient, set up by the Min system, which is the focus of this Primer. As is true for many fascinating molecular mechanisms, the first inkling came from the behavior of cells in which this system was broken.
母细胞通常需要仔细选择细胞分裂的位置，因为这将决定子细胞的大小和形状。通过二分分裂进行分裂的杆状细菌，如大肠杆菌，通常在细胞的中点标记它们的细胞分裂位点，以使子细胞的大小和形状大致相等。那么，大肠杆菌如何知道自己的中点在哪里呢？它的细胞极由前一次细胞分裂定义，但由于大肠杆菌通过在其长度上均匀地掺入新的细胞壁和膜来生长，因此在细胞中点的新的未来细胞分裂位点是新生成的，并且没有已知的预先存在的标记物。选择新的中点的一种方法是测量从两个相对的细胞极到的距离，使用一种可以识别那些极上的标记物并定义离两个标记物最远的点的系统。这将需要两个极性标记物以相等的强度对细胞分裂产生负向作用。结果将是一个浓度梯度，负调节剂的浓度在细胞中点最低，离两个细胞极最远。事实证明，大肠杆菌和一些其他杆状细菌使用由 Min 系统设置的负向形态发生梯度来选择它们的细胞中点，Min 系统是本概述的重点。与许多迷人的分子机制一样，第一个线索来自于这个系统被破坏的细胞的行为。
