Cytonemes are specialized filopodia that mediate paracrine signaling in Drosophila and other animals. Studies using fluorescence confocal microscopy (CM) established their general paths, cell targets, and essential roles in signaling. To investigate details unresolvable by CM, we used high-pressure freezing and EM to visualize cytoneme structures, paths, contents, and contacts. We observed cytonemes previously seen by CM in the Drosophila wing imaginal disc system, including disc, tracheal air sac primordium (ASP), and myoblast cytonemes, and identified cytonemes extending into invaginations of target cells, and cytonemes connecting ASP cells and connecting myoblasts. Diameters of cytoneme shafts vary between repeating wide (206 ± 51.8 nm) and thin (55.9 ± 16.2 nm) segments. Actin, ribosomes, and membranous compartments are present throughout; rough ER and mitochondria are in wider proximal sections. These results reveal novel structural features of filopodia and provide a basis for understanding cytoneme cell biology and function.

中文翻译：

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具有复杂几何形状和组成的胞嘧啶延伸到靶细胞的内陷。

胞浆是专门的丝状伪足，在果蝇和其他动物中介导旁分泌信号传导。使用荧光共聚焦显微镜（CM）的研究确定了它们的一般路径，细胞靶标以及在信号传导中的重要作用。为了研究CM无法解决的细节，我们使用了高压冷冻和EM来可视化细胞因子的结构，路径，含量和接触。我们观察到果蝇翼想象的椎间盘系统中CM先前观察到的细胞因子，包括椎间盘，气管气囊原基（ASP）和成肌细胞细胞因子，并鉴定了延伸到靶细胞内陷的细胞因子，以及连接ASP细胞和连接成肌细胞的细胞因子。细胞因子杆的直径在重复的宽段（206±51.8 nm）和薄段（55.9±16.2 nm）之间变化。肌动蛋白，核糖体和膜区室始终存在。较粗的ER和线粒体位于较宽的近端区域。这些结果揭示了丝状伪足的新型结构特征，并为理解细胞因子细胞生物学和功能提供了基础。