Bolourani Parvin, Spiegelman George, Weeks Gerald
Department of Microbiology and Immunology, Life Sciences Centre, University of British Columbia, Vancouver, Canada.
Eukaryot Cell. 2010 Nov;9(11):1728-33. doi: 10.1128/EC.00141-10. Epub 2010 Sep 10.
During the aggregation of Dictyostelium cells, signaling through RasG is more important in regulating cyclic AMP (cAMP) chemotaxis, whereas signaling through RasC is more important in regulating the cAMP relay. However, RasC is capable of substituting for RasG for chemotaxis, since rasG⁻ cells are only partially deficient in chemotaxis, whereas rasC⁻/rasG⁻ cells are totally incapable of chemotaxis. In this study we have examined the possible functional overlap between RasG and RasC in vegetative cells by comparing the vegetative cell properties of rasG⁻, rasC⁻, and rasC⁻/rasG⁻ cells. In addition, since RasD, a protein not normally found in vegetative cells, is expressed in vegetative rasG⁻ and rasC⁻/rasG⁻ cells and appears to partially compensate for the absence of RasG, we have also examined the possible functional overlap between RasG and RasD by comparing the properties of rasG⁻ and rasC⁻/rasG⁻ cells with those of the mutant cells expressing higher levels of RasD. The results of these two lines of investigation show that RasD is capable of totally substituting for RasG for cytokinesis and growth in suspension, whereas RasC is without effect. In contrast, for chemotaxis to folate, RasC is capable of partially substituting for RasG, but RasD is totally without effect. Finally, neither RasC nor RasD is able to substitute for the role that RasG plays in regulating actin distribution and random motility. These specificity studies therefore delineate three distinct and none-overlapping functions for RasG in vegetative cells.
在盘基网柄菌细胞聚集过程中，通过RasG的信号传导在调节环磷酸腺苷（cAMP）趋化性方面更为重要，而通过RasC的信号传导在调节cAMP中继方面更为重要。然而，RasC能够替代RasG进行趋化，因为rasG⁻细胞在趋化方面仅部分缺陷，而rasC⁻/rasG⁻细胞则完全丧失趋化能力。在本研究中，我们通过比较rasG⁻、rasC⁻和rasC⁻/rasG⁻细胞的营养细胞特性，研究了营养细胞中RasG和RasC之间可能的功能重叠。此外，由于营养细胞中通常不存在的蛋白质RasD在营养性rasG⁻和rasC⁻/rasG⁻细胞中表达，并且似乎部分补偿了RasG的缺失，我们还通过比较rasG⁻和rasC⁻/rasG⁻细胞与表达更高水平RasD的突变细胞的特性，研究了RasG和RasD之间可能的功能重叠。这两项研究结果表明，RasD能够完全替代RasG进行胞质分裂和悬浮生长，而RasC则无此作用。相比之下，对于向叶酸的趋化，RasC能够部分替代RasG，但RasD则完全无效。最后，RasC和RasD都不能替代RasG在调节肌动蛋白分布和随机运动中所起的作用。因此，这些特异性研究描绘了营养细胞中RasG的三种不同且不重叠的功能。
