Intercalation allows cells to exchange positions in a spatially oriented manner in an array of diverse processes, spanning convergent extension in embryonic gastrulation to the formation of tubular organs. However, given the co-occurrence of cell intercalation and changes in cell shape, it is sometimes difficult to ascertain their respective contribution to morphogenesis. A well-established model to analyse intercalation, particularly in tubular organs, is the Drosophila tracheal system. There, fibroblast growth factor (FGF) signalling at the tip of the dorsal branches generates a ‘pulling’ force believed to promote cell elongation and cell intercalation, which account for the final branch extension. Here, we used a variety of experimental conditions to study the contribution of cell elongation and cell intercalation to morphogenesis and analysed their mutual requirements. We provide evidence that cell intercalation does not require cell elongation and vice versa. We also show that the two cell behaviours are controlled by independent but simultaneous mechanisms, and that cell elongation is sufficient to account for full extension of the dorsal branch, while cell intercalation has a specific role in setting the diameter of this structure. Thus, rather than viewing changes in cell shape and cell intercalation as just redundant events that add robustness to a given morphogenetic process, we find that they can also act by contributing to different features of tissue architecture.

插入允许细胞在一系列不同的过程中以空间定向的方式交换位置，跨越胚胎原肠形成中的会聚延伸到管状器官的形成。然而，鉴于细胞嵌入和细胞形状变化的共同发生，有时很难确定它们各自对形态发生的贡献。一个成熟的模型来分析插层，特别是在管状器官中，是果蝇气管系统。在那里，背侧分支尖端的成纤维细胞生长因子 (FGF) 信号会产生一种“拉力”，据信可促进细胞伸长和细胞嵌入，这是最终分支延伸的原因。在这里，我们使用各种实验条件来研究细胞伸长和细胞嵌入对形态发生的贡献，并分析了它们的相互要求。我们提供的证据表明细胞嵌入不需要细胞伸长，反之亦然。我们还表明，这两种细胞行为受独立但同时发生的机制控制，细胞伸长足以解释背侧分支的完全伸展，而细胞嵌入在设置该结构的直径方面具有特定作用。因此，