Bloomfield Gareth, Traynor David, Sander Sophia P, Veltman Douwe M, Pachebat Justin A, Kay Robert R
MRC Laboratory of Molecular Biology, Cambridge, United Kingdom.
Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom.
Elife. 2015 Mar 27;4:e04940. doi: 10.7554/eLife.04940.
Cells use phagocytosis and macropinocytosis to internalise bulk material, which in phagotrophic organisms supplies the nutrients necessary for growth. Wildtype Dictyostelium amoebae feed on bacteria, but for decades laboratory work has relied on axenic mutants that can also grow on liquid media. We used forward genetics to identify the causative gene underlying this phenotype. This gene encodes the RasGAP Neurofibromin (NF1). Loss of NF1 enables axenic growth by increasing fluid uptake. Mutants form outsized macropinosomes which are promoted by greater Ras and PI3K activity at sites of endocytosis. Relatedly, NF1 mutants can ingest larger-than-normal particles using phagocytosis. An NF1 reporter is recruited to nascent macropinosomes, suggesting that NF1 limits their size by locally inhibiting Ras signalling. Our results link NF1 with macropinocytosis and phagocytosis for the first time, and we propose that NF1 evolved in early phagotrophs to spatially modulate Ras activity, thereby constraining and shaping their feeding structures.
细胞利用吞噬作用和巨胞饮作用内化大量物质，在吞噬营养生物中，这些物质为生长提供必要的营养。野生型盘基网柄菌变形虫以细菌为食，但几十年来，实验室研究一直依赖于也能在液体培养基上生长的无菌突变体。我们利用正向遗传学来鉴定这种表型背后的致病基因。该基因编码RasGAP神经纤维瘤蛋白（NF1）。NF1的缺失通过增加液体摄取实现无菌生长。突变体形成超大的巨胞饮体，这是由内吞作用位点上更强的Ras和PI3K活性所促进的。相关地，NF1突变体可以通过吞噬作用摄取比正常更大的颗粒。一个NF1报告基因被招募到新生的巨胞饮体上，这表明NF1通过局部抑制Ras信号传导来限制它们的大小。我们的结果首次将NF1与巨胞饮作用和吞噬作用联系起来，并且我们提出NF1在早期吞噬营养生物中进化，以在空间上调节Ras活性，从而限制并塑造它们的摄食结构。
