Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058, USA.
Biol Chem. 2011 Aug;392(8-9):813-29. doi: 10.1515/BC.2011.083.
Septins are essential for cytokinesis in Saccharomyces cerevisiae, but their precise roles remain elusive. Currently, it is thought that before cytokinesis, the hourglass-shaped septin structure at the mother-bud neck acts as a scaffold for assembly of the actomyosin ring (AMR) and other cytokinesis factors. At the onset of cytokinesis, the septin hourglass splits to form a double ring that sandwiches the AMR and may function as diffusion barriers to restrict diffusible cytokinesis factors to the division site. Here, we show that in cells lacking the septin Cdc10 or the septin-associated protein Bud4, the septins form a ring-like structure at the mother-bud neck that fails to re-arrange into a double ring early in cytokinesis. Strikingly, AMR assembly and constriction, the localization of membrane-trafficking and extracellular-matrix-remodeling factors, cytokinesis, and cell-wall-septum formation all occur efficiently in cdc10Δ and bud4Δ mutants. Thus, diffusion barriers formed by the septin double ring do not appear to be critical for S. cerevisiae cytokinesis. However, an AMR mutation and a septin mutation have synergistic effects on cytokinesis and the localization of cytokinesis proteins, suggesting that tethering to the AMR and a septin diffusion barrier may function redundantly to localize proteins to the division site.
在酿酒酵母中， septins 对于胞质分裂是必不可少的，但它们的确切作用仍难以捉摸。目前，人们认为在胞质分裂之前，母-芽颈部的沙漏状 septin 结构作为肌动球蛋白环（AMR）和其他胞质分裂因子组装的支架。在胞质分裂开始时， septin 沙漏分裂形成一个双环，夹在 AMR 之间，可能作为扩散障碍，将可扩散的胞质分裂因子限制在分裂部位。在这里，我们表明在缺乏 septin Cdc10 或 septin 相关蛋白 Bud4 的细胞中， septins 在母-芽颈部形成一个环状结构，在胞质分裂早期无法重新排列成双环。引人注目的是，AMR 组装和收缩、膜运输和细胞外基质重塑因子的定位、胞质分裂和细胞壁-隔膜形成都在 cdc10Δ 和 bud4Δ 突变体中有效地发生。因此， septin 双环形成的扩散障碍似乎不是酿酒酵母胞质分裂的关键。然而，AMR 突变和 septin 突变对胞质分裂和胞质分裂蛋白的定位有协同作用，这表明与 AMR 和 septin 扩散障碍的连接可能冗余地将蛋白质定位到分裂部位。
