Freie Universität Berlin, Fachbereich Biologie, Chemie und Pharmazie, Institut für Biologie - Neurobiologie, Königin-Luise Strasse 1-3, 14195 Berlin, Germany.
Freie Universität Berlin, Fachbereich Biologie, Chemie und Pharmazie, Institut für Biologie - Neurobiologie, Königin-Luise Strasse 1-3, 14195 Berlin, Germany.
Arthropod Struct Dev. 2021 Mar;61:101012. doi: 10.1016/j.asd.2020.101012. Epub 2021 Feb 19.
The retinal mosaics of many insects contain different ommatidial subtypes harboring photoreceptors that are both molecularly and morphologically specialized for comparing between different wavelengths versus detecting the orientation of skylight polarization. The neural circuits underlying these different inputs and the characterization of their specific cellular elements are the subject of intense research. Here we review recent progress on the description of both assembly and function of color and skylight polarization circuitry, by focusing on two cell types located in the distal portion of the medulla neuropil of the fruit fly Drosophila melanogaster's optic lobes, called Dm8 and Dm9. In the main part of the retina, Dm8 cells fall into two molecularly distinct subtypes whose center becomes specifically connected to either one of randomly distributed 'pale' or 'yellow' R7 photoreceptor fates during development. Only in the 'dorsal rim area' (DRA), both polarization-sensitive R7 and R8 photoreceptors are connected to different Dm8-like cell types, called Dm-DRA1 and Dm-DRA2, respectively. An additional layer of interommatidial integration is introduced by Dm9 cells, which receive input from multiple neighboring R7 and R8 cells, as well as providing feedback synapses back into these photoreceptors. As a result, the response properties of color-sensitive photoreceptor terminals are sculpted towards being both maximally decorrelated, as well as harboring several levels of opponency (both columnar as well as intercolumnar). In the DRA, individual Dm9 cells appear to mix both polarization and color signals, thereby potentially serving as the first level of integration of different celestial stimuli. The molecular mechanisms underlying the establishment of these synaptic connections are beginning to be revealed, by using a combination of live imaging, developmental genetic studies, and cell type-specific transcriptomics.
许多昆虫的视网膜镶嵌物包含不同的小眼亚型，这些小眼亚型中的感光器在分子和形态上都专门用于比较不同波长和检测天空偏振光的方向。这些不同输入的神经回路及其特定细胞元件的特征是当前研究的热点。在这里，我们通过关注位于果蝇（Drosophila melanogaster）光脑中神经髓质远端的两种细胞类型 Dm8 和 Dm9，回顾了最近在描述颜色和天空偏振光电路的组装和功能方面的进展。在视网膜的主要部分，Dm8 细胞分为两种分子上明显不同的亚型，其中心在发育过程中与随机分布的“苍白”或“黄色”R7 感光器命运之一特异性连接。只有在“背缘区”（DRA）中，偏振敏感的 R7 和 R8 感光器分别与不同的 Dm8 样细胞类型 Dm-DRA1 和 Dm-DRA2 连接。Dm9 细胞引入了另一个小眼间整合层，它接收来自多个相邻 R7 和 R8 细胞的输入，并向这些感光器提供反馈突触。结果，对颜色敏感的感光器末端的反应特性被塑造为最大程度去相关，并且具有几个级别的拮抗作用（柱状和柱间）。在 DRA 中，单个 Dm9 细胞似乎混合了偏振和颜色信号，从而可能成为不同天体刺激整合的第一级。通过使用活体成像、发育遗传研究和细胞类型特异性转录组学的组合，正在揭示建立这些突触连接的分子机制。
