Abstract
摘要:本計畫的主要目標是要在一個以果蠅為模組的系統下,研究在神經修剪作用的過程中,神經元微管的調控機制。對於神經系統的本身功能而言,神經迴路的精確連接是必要的,在發育階段中經常需要神經系統的重塑來提高連接之精準度。神經修剪作用,對發育中的神經系統而言是一個重塑機制,高度調控的自我毀壞程序;可選擇性的移除特定神經部位,卻不會造成神經細胞的死亡。神經修剪作用不僅在發育階段中需要神經系統的重塑來提高連接之精準度,也允許神經系統以調控神經連結的方式來反應損傷或疾病的情況。因此,在神經修剪作用中任何錯誤的調控會替神經元帶來災難的結果,並且造成一些神經退化性疾病的發生。最近的研究指出神經微管斷裂不僅是神經修剪作用中最早期的徵兆,也是神經損傷與疾病中神經退化的前兆。因此,神經微管的完整性對於神經纖維的正常功能是非常重要的,如果調控失敗將導致神經纖維的退化。例如,細胞微管蛋白之分子伴侶(tubulinspecificchaperoneE,Tbce)的突變,在模擬嚴重人類脊髓性肌肉萎縮症(SMA)的小鼠模式之漸進運動神經病變(progressivemotorneuropathy,PMN)中被發現。近來我們的研究指出Ik2和Spindle-F(Spn-F)在早期神經修剪的步驟–神經樹突的切除(dendritesevering)中扮演重要角色,並且影響部份細胞微管的穩定性在果蠅細胞培養中。此外我們發現了一個前未研究的微管切除蛋白,Kataninp60-like1(Kat-60L1),並證明其可在果蠅的感覺神經修剪作用中促進微管的斷裂。然而Ik2和Spn-F如何影響微管斷裂,以及Kat-60L1的活性如何被調控,其分子機制仍然不明。因此我們提議在果蠅神經修剪作用時,研究Ik2和Spn-F如何調控神經微管,以及Kat-60L1的活性如何被正向地和負向地調控。此研究的結果可以提供更多深入的了解,在果蠅神經修剪時神經微管的調控,以及理解神經損傷和神經退化疾病在發育理論階段的發病機制,並借此發展疾病治療的策略。
Abstract: The goal of this proposal is to uncover the underlying mechanism of microtubuledynamic regulation in neuronal pruning by using Drosophila as a model system. The precisewiring of neuronal circuitry is important for the proper function of nervous system, and thatoften requires neuronal remodeling to refine their connections during development. Neuronalpruning, one of the remodeling mechanisms for the developing nervous systems, is a highlyregulated cellular process that selectively eliminates specific parts of neuronal fibers withoutcausing cell death. Pruning is not only observed in the developing nervous systems to refinetheir neural connections, but also in the adult nervous systems to respond to neuronal injuriesand diseases. Thus, any mis-regulation of pruning activity may cause catastrophicconsequences in neurons, and would contribute to the pathogenesis of certainneurodegenerative diseases. Recent studies have demonstrated that microtubule breakdown isthe earliest cellular event observed in all three types of pruning, even preceding thepreviously reported neurofilament breakdown. Therefore, the maintenance of microtubuleintegrity is important for the normal function of neuronal processes, and its deregulation willresult in neurite degeneration. For example, the tubulin specific chaperone E (Tbce) is foundmutated in the spontaneously occurred progressive motor neuropathy (pmn) mouse model,which mimics severe form of human spinal muscular atrophy (SMA). We have identified thatboth Ik2 kinase and Spindle-F (Spn-F) play a crucial role in dendrite severing duringneuronal pruning, and both affect the stability of certain microtubules in S2 cells. We alsoidentified a previously uncharacterized protein Katanin p60-like 1 (Kat-60L1) with putativemicrotubule-severing activity and demonstrated that Kat-60L1 can facilitate localmicrotubule breakdown in the dendrite-severing sites of Drosophila sensory neurons.However, the underlying molecular mechanisms by which Ik2 and Spn-F initiate localmicrotubule breakdown at the dendrite-severing sites, and by which Kat-60L1 activity isregulated to sever microtubules at the proximal dendrites, remain unknown. Thus, I plan toinvestigate the mechanisms how Ik2 kinase and Spn-F affect microtubule dynamics duringdendrite pruning, and how Kat-60L1 activity is regulated by positive and negative regulatorsin dendrite severing. The results from this study will greatly advance our understanding onthe regulation of microtubule dynamics in neuronal pruning, and provide valuable insights inunderstanding the pathological mechanisms and in developing therapeutic strategies ofneuronal injury and neurodegenerative disorders.
Keyword(s)
神經退化
神經樹突
神經修剪
細胞微管
neurodegeneration
dendrite
neuronal pruning
microtubule