Genetic programmes for dendrite regrowth after pruning in Drosophila - mechanistic and functional aspects

发育过程中成熟神经元连接性的建立通常发生在进行性事件和退行性事件的不同阶段。特别是，连接性可以通过调节神经突起和突触的退化来重塑，这一过程被称为修剪。在这种情况下，神经元可以通过改变连接性来再生新的神经突起或突触。虽然从无脊椎动物到哺乳动物都描述了这种重塑的几个例子，但关于修剪和再生是如何在分子水平上协调的，以及修剪和/或再生失败对神经元功能的影响，人们知之甚少。果蝇周围感觉神经元是研究修剪机制的一个很好的模型，它在变态开始时修剪幼虫的感觉树突，然后以成虫特有的形态再生它们。虽然最初的树枝修剪背后的分子机制开始出现，但对树枝的再生长知之甚少。我们以前可以证明，树突修剪在翻译起始水平上受到调控，显然是为了限制蛋白质的生物合成。相反，我们发现促进蛋白质生物合成的分子途径-雷帕霉素(TOR)途径的靶点，以及mRNA剪接-在修剪后以一种明显特异的方式需要树突重新生长。这就提出了这样一个问题：蛋白质生物合成的全球上调是否足以促进树突再生，或者特定的mRNAs是否必须正确拼接和翻译。此外，树突再生如何与成人感觉神经元功能有关尚不清楚。在这里，我们建议系统地确定修剪后树枝重新生长的遗传基础。为此，我们将(1)进行候选RNAi筛选，以确定树突再生的调控基因网络；(2)分别使用候选方法和RNAseq来确定TOR和剪接因子的下游靶点；以及(3)开发成人感觉神经元功能的功能行为分析，以评估再生(也包括修剪)缺陷的影响。我们的项目将为修剪、再生和神经元功能之间的相互作用提供重要的见解。

The establishment of the mature neuronal connectivity during development often occurs in distinct phases of progressive and regressive events. In particular, connectivity can be remodeled through regulated degeneration of neurites and synapses, a process known as pruning. In such cases, neurons can regrow new neurites or synapses with altered connectivity. While several examples of such remodeling have been described from invertebrates to mammals, little is known about how pruning and regrowth are coordinated at the molecular level and what the consequences of failed pruning and/or regrowth are for neuronal function. A well-suited model to study pruning mechanisms are Drosophila peripheral sensory neurons, which prune their larval sensory dendrites at the onset of metamorphosis and later regrow them with adult-specific morphology. While the molecular mechanisms underlying the initial dendrite pruning are beginning to emerge, little is known about dendrite regrowth. We could previously show that dendrite pruning is regulated at the level of translation initiation, apparently in order to limit protein biosynthesis. In contrast, we found that molecular pathways promoting protein biosynthesis – the Target of Rapamycin (TOR) pathway, and also mRNA splicing, are required for dendrite regrowth after pruning in an apparently specific manner. This raises the question as to whether a global upregulation of protein biosynthesis is sufficient to promote dendrite regrowth, or whether specific mRNAs must be spliced correctly and translated. In addition, it is not clear how dendrite regrowth is linked to adult sensory neuron function. Here, we propose to systematically identify the genetic basis for dendrite regrowth after pruning. To this end, we will (1) perform candidate RNAi screens to identify the regulatory gene networks for dendrite regrowth; (2) identify downstream targets of TOR and splicing factors using candidate approaches and RNAseq, respectively and (3) develop functional behavioral assays for adult sensory neuron function to assess the effects of regrowth (and also pruning) defects. Our project will provide important insights into the interplay between pruning, regrowth, and neuronal function.