Cohen B, Simcox A A, Cohen S M
Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030.
Development. 1993 Feb;117(2):597-608. doi: 10.1242/dev.117.2.597.
The primordia of the thoracic imaginal discs of the Drosophila embryo originate as groups of cells spanning the parasegment boundary. We present evidence that the thoracic imaginal primordia are allocated in response to signals from the wingless (wg) and decapentaplegic (dpp) gene products. Rows of cells that express wg intersect rows of cells that express dpp to form a ladder-like pattern in the ectoderm of the germ band extended embryo. The imaginal primordia originate as groups of cells which lie near these intersection points. We have used a molecular probe derived from the Distal-less (Dll) gene to show that this population contains progenitor cells for both the dorsal (i.e. wing) and ventral (i.e. leg) discs. Although we show that Dll function is not required for allocation of imaginal cells, activation of an early Dll enhancer may serve as a molecular marker for allocation. A group of cells, which includes the imaginal progenitors, activate this enhancer in response to intercellular signals from wg and perhaps from dpp. We have used a conditional allele of wg to show that wg function is transiently required for both allocation of the imaginal primordia and for initiation of Dll expression in these cells during the brief interval when wg and dpp form the ladder-like pattern. Allocation of the imaginal primordium and activation of Dll expression appear to be parallel responses to a single set of positional cues.
果蝇胚胎胸节成虫盘的原基起源于跨越副节边界的细胞群。我们提供的证据表明，胸节成虫原基是根据无翅（wg）和脱壳蛋白（dpp）基因产物发出的信号进行分配的。表达wg的细胞行与表达dpp的细胞行相交，在胚带延伸胚胎的外胚层中形成梯状模式。成虫原基起源于位于这些交点附近的细胞群。我们使用了一种源自远端缺失（Dll）基因的分子探针，以表明这群细胞包含背侧（即翅）和腹侧（即腿）盘的祖细胞。尽管我们表明Dll功能对于成虫细胞的分配不是必需的，但早期Dll增强子的激活可能作为分配的分子标记。包括成虫祖细胞在内的一群细胞，响应来自wg以及可能来自dpp的细胞间信号激活该增强子。我们使用wg的条件等位基因表明，在wg和dpp形成梯状模式的短暂间隔期间，wg功能对于成虫原基的分配以及这些细胞中Dll表达的启动都是短暂需要的。成虫原基的分配和Dll表达的激活似乎是对单一位置线索集的平行反应。
