Translational Control of Early Neurogenesis in Drosophila

描述(申请人提供)：神经发生的早期步骤是从幼稚的神经上皮细胞产生神经元前体细胞。虽然促进早期神经发生的转录因子和几个信号通路已经被确定，但确保从神经上皮细胞产生准确数量的神经元前体的机制仍有待进一步确定。果蝇周围神经系统中感觉器官前体(SOP)的形成是了解早期神经发生的最佳模型系统之一。少数细胞，称为原神经丛，表达原神经细胞基因，编码基本螺旋环状螺旋(BHLH)蛋白，并具有发育为SOP的能力。SOP通过神经源性基因(如Notch和Delta)的作用从神经丛中出现，这些基因在SOP中维持神经基因的高水平表达，在邻近的上皮细胞中保持低水平的表达。配体Delta与Notch受体结合，Notch受体通过无毛[SU(H)]抑制子和裂解复合体增强子的作用调节神经基因的差异表达。Sens是一种具有四个锌指的核蛋白，在SOP中上调和维持原神经基因的表达，在SOP中表达水平很高。在原神经丛的相邻上皮细胞中，SENS低水平表达并抑制原神经基因的表达。SENS在表达和功能上的这些差异对于SOP的正确形成是必不可少的。准确产生神经前体细胞所需的这些基因的差异调控机制尚不清楚。最近，我们产生了microRNA-9a功能丧失突变果蝇，并发现microRNA-9a通常通过下调Sens的表达来抑制非SOP细胞中的神经元命运。在这个应用中，我们建议进一步剖析原神经基因和microRNA-9a之间的反馈环。利用遗传筛选，我们还将确定microRNA-9a的其他关键靶点，包括对早期神经发生重要的潜在新角色。由于许多从苍蝇到哺乳动物的microRNAs在核苷酸水平上是100%保守的，我们的发现也将对哺乳动物的神经发生具有重要意义，并可能为神经发育障碍提供新的见解。

DESCRIPTION (provided by applicant): An early step in neurogenesis is the generation of neuronal precursor cells from the naive neuroepithelium. Although transcription factors and several signaling pathways that promote early neurogenesis have been identified, the mechanisms that ensure the generation of precise numbers of neuronal precursors from the neuroepithelial cells remain to be further defined. One of the best model systems for understanding early neurogenesis is sensory organ precursor (SOP) formation in the Drosophila peripheral nervous system. A small number of cells, known as the proneural cluster, express proneural genes that encode basic helix loop helix (bHLH) proteins and become competent to develop into SOPs. The SOP emerges from the proneural cluster through the actions of "neurogenic" genes (e.g., Notch and Delta) that maintain proneural gene expression at high levels in the SOP and at low levels in adjacent epithelial cells. The ligand Delta binds to the Notch receptor, which in turn regulates the differential expression of proneural genes through the actions of Suppressor of hairless [Su(H)] and the Enhancer of split complex. Senseless (Sens), a nuclear protein with four zinc fingers that is required to upregulate and maintain proneural gene expression in SOPs, is expressed at a high level in SOPs. In adjacent epithelial cells in the proneural cluster, Sens is expressed at a low level and suppresses proneural gene expression. These differences in the expression and function of Sens are essential for proper SOP formation. The mechanism of differential regulation of these genes required for the accurate production of neuronal precursor cells is unclear. Recently, we generated microRNA-9a loss-of- function mutant flies and found that microRNA-9a normally inhibits neuronal fate in non-SOP cells by downregulating Sens expression. In this application, we propose to further dissect the feedback loops between proneural genes and microRNA-9a. Using genetic screens, we will also identify other key targets of microRNA- 9a, including potential novel players important for early neurogenesis. Since many microRNAs are 100% conserved at the nucleotide level from flies to mammals, our findings will have important implications for mammalian neurogenesis as well and may provide novel insights into neurodevelopmental disorders.