Laminar arrangement of neural connections is a fundamental feature of neural circuit organization. Identifying mechanisms that coordinate neural connections within correct layers is thus vital for understanding how neural circuits are assembled. In the medulla of the Drosophila visual system neurons form connections within ten parallel layers. The M3 layer receives input from two neuron types that sequentially innervate M3 during development. Here we show that M3-specific innervation by both neurons is coordinated by Drosophila Fezf (dFezf), a conserved transcription factor that is selectively expressed by the earlier targeting input neuron. In this cell, dFezf instructs layer specificity and activates the expression of a secreted molecule (Netrin) that regulates the layer specificity of the other input neuron. We propose that employment of transcriptional modules that cell-intrinsically target neurons to specific layers, and cell-extrinsically recruit other neurons is a general mechanism for building layered networks of neural connections.

中文翻译：

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果蝇 Fezf 通过细胞内在和细胞外机制协调层流特异性连接

神经连接的层状排列是神经回路组织的基本特征。因此，识别在正确层内协调神经连接的机制对于理解神经回路的组装方式至关重要。在果蝇视觉系统的髓质中，神经元在十个平行层内形成连接。M3 层接收来自两种神经元类型的输入，这些神经元类型在发育过程中依次支配 M3。在这里，我们展示了两个神经元的 M3 特异性神经支配由果蝇 Fezf (dFezf) 协调，这是一种保守的转录因子，由较早的靶向输入神经元选择性表达。在该细胞中，dFezf 指示层特异性并激活调节其他输入神经元层特异性的分泌分子 (Netrin) 的表达。