Freeman M
MRC Laboratory of Molecular Biology, Cambridge, UK.
Development. 1997 Jan;124(2):261-70. doi: 10.1242/dev.124.2.261.
Cells in the Drosophila eye are determined by inductive signalling. Here I describe a new model of eye development that explains how simple intercellular signals could specify the diverse cell types that constitute the ommatidium. This model arises from the recent observation that the Drosophila homologue of the EGF receptor (DER) is used reiteratively to trigger the differentiation of each of the cell types--successive rounds of DER activation recruit first the photoreceptors, then cone and finally pigment cells. It seems that a cell's identity is not determined by the specific signal that induces it, but is instead a function of the state of the cell when it receives the signal. DER signalling is activated by the ligand, Spitz, and inhibited by the secreted protein, Argos. Spitz is initially produced by the central cells in the ommatidium and diffuses over a small distance. Argos has a longer range, allowing it to block more distal cells from being activated by low levels of Spitz; I have termed this interplay between a short-range activator and a long-range inhibitor 'remote inhibition'. Since inductive signalling is common in many organisms and its components have been conserved, it is possible that the logic of signalling may also be conserved.
果蝇眼中的细胞是由诱导信号决定的。在此，我描述一种新的眼睛发育模型，该模型解释了简单的细胞间信号如何能够指定构成小眼的多种细胞类型。这个模型源于最近的一项观察结果，即表皮生长因子受体（DER）的果蝇同源物被反复用于触发每种细胞类型的分化——连续几轮的DER激活首先招募光感受器，然后是视锥细胞，最后是色素细胞。似乎细胞的身份不是由诱导它的特定信号决定的，而是接收信号时细胞状态的函数。DER信号由配体Spitz激活，并被分泌蛋白Argos抑制。Spitz最初由小眼中的中央细胞产生，并在小范围内扩散。Argos的作用范围更远，使其能够阻止更多远端细胞被低水平的Spitz激活；我将这种短程激活剂和远程抑制剂之间的相互作用称为“远程抑制”。由于诱导信号在许多生物体中很常见，并且其组成部分已经保守下来，因此信号传导的逻辑也有可能是保守的。
