Mechanisms that underlie Drosophila visual center

在果蝇中，光感受器细胞拓扑地将其轴突发送到板层和髓质神经节。DPP信号通过控制gcm的表达来介导正确的R轴突投射模式所需的板层胶质细胞的成熟。在DWnt 4突变体中，腹侧视网膜轴突错误投射到背侧椎板。DWnt 4通常在发育中的板层的腹侧一半中表达，并且沿着腹侧视网膜轴突检测到DWnt 4蛋白。对Wnt信号通路的基因分析表明，DWnt 4在视网膜轴突导向中起直接作用. R轴突通过传递诱导信号Hedgehog（Hh）触发板层神经元的增殖和分化。我们发现，bHLH-PAS转录因子Single-minded（Sim）是由Hh诱导的，是板层神经元与R轴突联系所必需的。在sim突变的大脑中，板层神经元不能与R轴突联系。这些数据揭示了一种新的机制，用于调节轴突和神经元细胞体之间的相互作用，建立精确的神经元网络。视神经节由视柄（英语：Optical stalk）（英语：Optical stalk）所支配，视柄由表面神经胶质（英语：surface glia）所组成。视柄是自主形成的，独立于R轴突投射。我们发现Fak 56 D编码的粘着斑激酶（FAK）和CdGAPr在视柄的形成中起重要作用.髓质神经母细胞的发育具有一定的空间顺序性，而原神经基因之一scute（l（1）sc）的致死性标志着神经上皮细胞向神经母细胞的转变。L（1）sc表达是短暂的，以同步和有序的“前神经波”向更外侧的NE细胞扫过。L（1）sc表达足以诱导NB，并且对于NB分化的及时开始是必需的。我们还发现JAK/STAT信号在NE细胞中被激活，并负调节前神经波的进展。

In Drosophila, photoreceptor cells topographically send their axons to the lamina and medulla ganglia.We found :1. DPP signaling mediates the maturation of the lamina glia required for the correct R axon projection pattern by controlling the expression of gcm.2. In DWnt4 mutants, ventral retinal axons misproject to the dorsal lamina. DWnt4 is normally expressed in the ventral half of the developing lamina and DWnt4 protein was detected along ventral retinal axons. Genetic analyses on Wnt signaling components suggest direct roles of DWnt4 for retinal axon guidance.3. R axons trigger proliferation and differentiation of lamina neurons by delivering the inductive signal, Hedgehog (Hh). We found that the bHLH-PAS transcription factor Single-minded (Sim) is induced by Hh in the lamina neurons and is required for the association of lamina neurons with R axons. In sim mutant brains, lamina neurons fail to associate with R axons. The data reveal a novel mechanism for regulation of the interaction between axons and neuronal cell bodies that establishes precise neuronal networks.4. R axons innervate optic ganglia through the tubular structure called the optic stalk, which consists of surface glia (SG). The optic stalk is formed autonomously, independently of R axon projection. We found Fak56D, encoding a Focal adhesion kinase (FAK) and CdGAPr play an important role in forming the optic stalk.5. Medulla neuroblasts develop sequentially in a spatially defined manner, and that lethal of scute (l(1)sc), one of the proneural genes, signals the transition of neuroepithelium to neuroblasts. L(1)sc expression is transient, progressing in a synchronized and ordered "proneural wave" that sweeps toward more lateral NE cells. L(1)sc expression is sufficient to induce NBs and is necessary for timely onset of NB differentiation. We also found that JAK/STAT signaling is activated in NE cells and negatively regulates proneural wave progression.