In the human and Drosophila color vision system, each photoreceptor neuron (cone cell in humans and R7/R8 photoreceptor cell in Drosophila) makes a stochastic decision to express a single photopigment of the same family with the exclusion of the others. While recent studies have begun to reveal the mechanisms that specify the generation of cone subtypes during development in mammals, nothing is known about how the mosaic of mutually exclusive cone subtypes is maintained in the mammalian retina. In Drosophila, recent work has led to the identification of several intrinsic factors that maintain the identity of R8 photoreceptor subtypes in adults. Whether and how extrinsic mechanisms are involved, however, remain unknown. In this study, we present evidence that supports that the Drosophila transsynaptic adhesion molecule Neurexin 1 (Dnrx-1) is required non-cell autonomously in R8p subtypes for the maintenance of R8y subtype identity. Silencing the activity of R8p subtypes caused a phenotype identical to that in dnrx-1 mutants. These results support a novel role for Nrx-1-dependent circuit activity in mediating the communication between R8 photoreceptor subtypes for maintaining the subtype identity in the retina.

中文翻译：

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Neurexin-1 依赖性电路活性是维持果蝇感光细胞亚型特性所必需的

在人类和果蝇的色觉系统中，每个感光神经元（人类的视锥细胞和果蝇的 R7/R8 感光细胞）都会做出随机决定，表达同一家族的单个感光色素，而排除其他感光色素。虽然最近的研究已经开始揭示哺乳动物发育过程中视锥细胞亚型产生的具体机制，但对于哺乳动物视网膜中如何维持相互排斥的视锥细胞亚型的嵌合体却一无所知。在果蝇中，最近的工作已经确定了维持成虫 R8 光感受器亚型特性的几种内在因素。然而，外在机制是否以及如何参与仍然未知。在这项研究中，我们提供的证据支持果蝇突触粘附分子 Neurexin 1 (Dnrx-1) 在 R8p 亚型中非细胞自主地需要以维持 R8y 亚型身份。沉默 R8p 亚型的活性会产生与 dnrx-1 突变体相同的表型。这些结果支持 Nrx-1 依赖性电路活动在介导 R8 光感受器亚型之间的通信以维持视网膜中亚型身份方面的新作用。