Department of Genetics, Cancer Research United Kingdom Cell Cycle Genetics Research Group, University of Cambridge, Cambridge CB2 3EH, United Kingdom.
Proc Natl Acad Sci U S A. 2012 Apr 10;109(15):5729-34. doi: 10.1073/pnas.1108537109. Epub 2012 Mar 26.
Mutations in Drosophila merry-go-round (mgr) have been known for over two decades to lead to circular mitotic figures and loss of meiotic spindle integrity. However, the identity of its gene product has remained undiscovered. We now show that mgr encodes the Prefoldin subunit counterpart of human von Hippel Lindau binding-protein 1. Depletion of Mgr from cultured cells also leads to formation of monopolar and abnormal spindles and centrosome loss. These phenotypes are associated with reductions of tubulin levels in both mgr flies and mgr RNAi-treated cultured cells. Moreover, mgr spindle defects can be phenocopied by depleting β-tubulin, suggesting Mgr function is required for tubulin stability. Instability of β-tubulin in the mgr larval brain is less pronounced than in either mgr testes or in cultured cells. However, expression of transgenic β-tubulin in the larval brain leads to increased tubulin instability, indicating that Prefoldin might only be required when tubulins are synthesized at high levels. Mgr interacts with Drosophila von Hippel Lindau protein (Vhl). Both proteins interact with unpolymerized tubulins, suggesting they cooperate in regulating tubulin functions. Accordingly, codepletion of Vhl with Mgr gives partial rescue of tubulin instability, monopolar spindle formation, and loss of centrosomes, leading us to propose a requirement for Vhl to promote degradation of incorrectly folded tubulin in the absence of functional Prefoldin. Thus, Vhl may play a pivotal role: promoting microtubule stabilization when tubulins are correctly folded by Prefoldin and tubulin destruction when they are not.
果蝇 merry-go-round（mgr）中的突变已被发现超过二十多年，导致有丝分裂形成环状和减数分裂纺锤体完整性丧失。然而，其基因产物的身份仍然未知。我们现在表明，mgr 编码人希佩尔-林道结合蛋白 1 的 Prefoldin 亚基对应物。培养细胞中 Mgr 的耗竭也会导致形成单极和异常纺锤体以及中心体丢失。这些表型与 mgr 果蝇和 mgr RNAi 处理的培养细胞中微管蛋白水平的降低有关。此外，mgr 纺锤体缺陷可以通过耗尽β-微管蛋白来表型模拟，表明 Mgr 功能对于微管蛋白的稳定性是必需的。mgr 幼虫大脑中的β-微管蛋白不稳定性不如 mgr 睾丸或培养细胞明显。然而，在幼虫大脑中表达转基因β-微管蛋白会导致微管蛋白不稳定性增加，表明 Prefoldin 可能仅在微管蛋白高水平合成时才需要。Mgr 与果蝇希佩尔-林道蛋白（Vhl）相互作用。两种蛋白质都与未聚合的微管蛋白相互作用，表明它们合作调节微管蛋白功能。因此，Mgr 与 Vhl 的共耗竭部分挽救了微管蛋白不稳定性、单极纺锤体形成和中心体丢失，这使我们提出了 Vhl 促进功能失调的 Prefoldin 缺失时未折叠微管蛋白降解的要求。因此，Vhl 可能发挥关键作用：当微管蛋白被 Prefoldin 正确折叠时促进微管稳定性，而当它们不正确折叠时促进微管蛋白破坏。
