Translational Control of Early Neurogenesis in Drosophila

描述（由申请人提供）：神经发生的早期步骤是从原始神经上皮生成神经前体细胞。虽然已经确定了促进早期神经发生的转录因子和几种信号通路，但确保神经上皮细胞产生精确数量的神经元前体的机制仍有待进一步确定。了解早期神经发生的最佳模型系统之一是果蝇周围神经系统的感觉器官前体（SOP）形成。被称为prooneural cluster的少数细胞表达prooneural基因，该基因编码基本螺旋环螺旋（bHLH）蛋白，并具有发育成SOPs的能力。通过“神经源性”基因（如Notch和Delta）的作用，SOP从前膜细胞簇中出现，这些基因在SOP中维持高水平的前膜基因表达，而在邻近上皮细胞中维持低水平的表达。配体Delta与Notch受体结合，进而通过无毛抑制因子（Suppressor of hairless [Su(H)]）和分裂复合体增强子（Enhancer of split complex）的作用调节前膜基因的差异表达。无意义蛋白（Sens）是一种具有四个锌指的核蛋白，在SOPs中需要上调和维持原基因的表达，在SOPs中表达水平很高。在前膜簇的邻近上皮细胞中，Sens低水平表达并抑制前膜基因的表达。Sens在表达和功能上的差异对于SOP的形成至关重要。神经元前体细胞精确产生所需的这些基因的差异调控机制尚不清楚。最近，我们在果蝇中产生了microRNA-9a功能缺失突变体，发现microRNA-9a通常通过下调Sens表达来抑制非sop细胞的神经元命运。在这个应用中，我们建议进一步剖析前基因和microRNA-9a之间的反馈回路。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参与者。由于从果蝇到哺乳动物的许多microrna在核苷酸水平上是100%保守的，我们的发现将对哺乳动物神经发生也有重要意义，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.