Jelsbak Lars, Søgaard-Andersen Lotte
Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.
J Microbiol Methods. 2003 Dec;55(3):829-39. doi: 10.1016/j.mimet.2003.08.007.
Formation of spatial patterns of cells from a mass of initially identical cells is a recurring theme in developmental biology. The dynamics that direct pattern formation in biological systems often involve morphogenetic cell movements. An example is fruiting body formation in the gliding bacterium Myxococcus xanthus in which an unstructured population of identical cells rearranges into an asymmetric, stable pattern of multicellular fruiting bodies in response to starvation. Fruiting body formation depends on changes in organized cell movements from swarming to aggregation. The aggregation process is induced and orchestrated by the cell-surface associated 17 kDa C-signal protein. C-signal transmission depends on direct contact between cells. Evidence suggests that C-signal transmission is geometrically constrained to cell ends and that productive C-signal transmission only occurs when cells engage in end-to-end contacts. Here, we review recent progress in the understanding of the pattern formation process that leads to fruiting body formation. Gliding motility in M. xanthus involves two polarly localized gliding machines, the S-machine depends on type IV pili and the A-machine seems to involve a slime extrusion mechanism. Using time-lapse video microscopy the gliding motility parameters controlled by the C-signal have been identified. The C-signal induces cells to move with increased gliding speeds, in longer gliding intervals and with decreased stop and reversal frequencies. The combined effect of the C-signal dependent changes in gliding motility behaviour is an increase in the net-distance travelled by a cell per minute. The identification of the motility parameters controlled by the C-signal in combination with the contact-dependent C-signal transmission mechanism have allowed the generation of a qualitative model for C-signal induced aggregation. In this model, the directive properties of the C-signal are a direct consequence of the contact-dependent signal-transmission mechanism, which is a local event involving direct contact between cells that results in a global organization of cells. This pattern formation process does not depend on a diffusible substance. Rather it depends on a cell-surface associated signal to direct the cells appropriately.
从大量初始相同的细胞形成细胞空间模式是发育生物学中反复出现的主题。指导生物系统中模式形成的动力学通常涉及形态发生细胞运动。一个例子是滑行细菌黄色粘球菌中的子实体形成，其中无结构的相同细胞群体在饥饿时重排为多细胞子实体的不对称、稳定模式。子实体形成取决于有组织的细胞运动从群体运动到聚集的变化。聚集过程由细胞表面相关的17 kDa C信号蛋白诱导和协调。C信号传递取决于细胞之间的直接接触。有证据表明，C信号传递在几何上受限于细胞末端，并且只有当细胞进行端对端接触时才会发生有效的C信号传递。在这里，我们回顾了在理解导致子实体形成的模式形成过程方面的最新进展。黄色粘球菌的滑行运动涉及两个极性定位的滑行机器，S机器依赖于IV型菌毛，A机器似乎涉及粘液挤压机制。使用延时视频显微镜已经确定了由C信号控制的滑行运动参数。C信号诱导细胞以更高的滑行速度、更长的滑行间隔以及更低的停止和反转频率移动。C信号依赖性滑行运动行为变化的综合作用是细胞每分钟净移动距离的增加。C信号控制的运动参数的识别与接触依赖性C信号传递机制相结合，使得能够生成C信号诱导聚集的定性模型。在这个模型中，C信号的定向特性是接触依赖性信号传递机制的直接结果，这是一个涉及细胞之间直接接触的局部事件，导致细胞的全局组织。这种模式形成过程不依赖于可扩散物质。相反，它依赖于细胞表面相关信号来适当地引导细胞。
