Role of Tropomyosin in Formin-mediated Contractile Ring Assembly in Fission Yeast
Role of Tropomyosin in Formin-mediated Contractile Ring Assembly in Fission Yeast
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DOI：
10.1091/mbc.e08-12-1201
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发表时间：
2009-04-15
影响因子：
3.3
通讯作者：
Kovar, David R.
中科院分区：
文献类型：
--
作者：
Skau, Colleen T.;Neidt, Erin M.;Kovar, David R.
像动物细胞一样，分裂酵母通过将肌动蛋白细丝组装成收缩环进行分裂。除了Forin CDC12p和Profilin外，收缩环组装还需要单一的原肌球蛋白亚型SpTm。CDC12P使肌动蛋白细丝成核，并保持与延长的带刺末端的连续联系，同时驱动Profilin-肌动蛋白的添加。SpTm被认为可以稳定成熟的肌丝，但目前尚不清楚SpTm如何定位于收缩环，以及SpTm是否在Cdc12P介导的肌动蛋白聚合中发挥直接作用。通过“整体”和“单丝”肌动蛋白微丝分析，我们发现，Cdc12P可以将SpTm募集到肌动蛋白微丝中，并且SpTm在CDc12P介导的肌动蛋白组装中具有不同的作用。SpTm本身可以抑制肌动蛋白细丝的伸长和解聚。然而，Cdc12p完全克服了Profilin和SpTm对肌动蛋白成核和带刺末端延长的联合抑制。此外，SpTm通过将伸长率提高两倍并允许它们端到端退火，增加了Cdc12P核肌动蛋白细丝的长度。相反，SpTm通过在退火丝中“捕获”Cdc12p或通过从带刺的末端解离Cdc12p，最终关闭了CDc12p介导的延伸。因此，SpTm在肌动蛋白聚合过程中和之后对收缩环的组装有多方面的贡献。
Like animal cells, fission yeast divides by assembling actin filaments into a contractile ring. In addition to formin Cdc12p and profilin, the single tropomyosin isoform SpTm is required for contractile ring assembly. Cdc12p nucleates actin filaments and remains processively associated with the elongating barbed end while driving the addition of profilin-actin. SpTm is thought to stabilize mature filaments, but it is not known how SpTm localizes to the contractile ring and whether SpTm plays a direct role in Cdc12p-mediated actin polymerization. Using "bulk" and single actin filament assays, we discovered that Cdc12p can recruit SpTm to actin filaments and that SpTm has diverse effects on Cdc12p-mediated actin assembly. On its own, SpTm inhibits actin filament elongation and depolymerization. However, Cdc12p completely overcomes the combined inhibition of actin nucleation and barbed end elongation by profilin and SpTm. Furthermore, SpTm increases the length of Cdc12p-nucleated actin filaments by enhancing the elongation rate twofold and by allowing them to anneal end to end. In contrast, SpTm ultimately turns off Cdc12p-mediated elongation by "trapping" Cdc12p within annealed filaments or by dissociating Cdc12p from the barbed end. Therefore, SpTm makes multiple contributions to contractile ring assembly during and after actin polymerization.