The abdomen of adult Drosophila, like that of other insects, is formed by a continuous epithelium spanning several segments. Each segment is subdivided into an anterior (A) and posterior (P) compartment, distinguished by activity of the selector gene engrailed (en) in P but not A compartment cells. Here we provide evidence that Hedgehog (Hh), a protein secreted by P compartment cells, spreads into each A compartment across the anterior and the posterior boundaries to form opposing concentration gradients that organize cell pattern and polarity. We find that anteriorly and posteriorly situated cells within the A compartment respond in distinct ways to Hhthey express different combinations of genes and form different cell types. They also form polarised structures that, in the anterior part, point down the Hh gradient and, in the posterior part, point up the gradient - therefore all structures point posteriorly. Finally, we show that ectopic Hh can induce cells in the middle of each A compartment to activate en. Where this happens, A compartment cells are transformed into an ectopic P compartment and reorganise pattern and polarity both within and around the transformed tissue. Many of these results are unexpected and lead us to reassess the role of gradients and compartments in patterning insect segments.

译文

与其他昆虫一样,成年果蝇的腹部是由横跨多个节段的连续上皮形成的。每个节段都分为前 (A) 和后 (P) 隔室,其特征是在P细胞中包含 (en) 的选择基因的活性,而不是隔室细胞。在这里,我们提供的证据表明,刺猬 (Hh) 是一种由P室细胞分泌的蛋白质,通过前后边界扩散到每个a室中,形成相反的浓度梯度,从而组织细胞模式和极性。我们发现,位于A区室前后的细胞以不同的方式对hh做出反应,它们表达不同的基因组合并形成不同的细胞类型。它们还形成极化结构,在前部指向Hh梯度,在后部指向梯度,因此所有结构都指向后部。最后,我们证明异位Hh可以诱导每个A室中间的细胞激活en。在发生这种情况的情况下,一个隔室细胞被转化为异位的P隔室,并在转化的组织内部和周围重组模式和极性。这些结果中有许多是出乎意料的,使我们重新评估了梯度和区室在昆虫节段构图中的作用。

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