Epithelial folding is a fundamental morphogenetic process that shapes planar epithelial sheets into complex three-dimensional structures. Multiple mechanisms can generate epithelial folds, including apical constriction, which acts locally at the cellular level, differential growth on the tissue scale, or buckling because of compression from neighboring tissues. Here, we investigate the formation of dorsally located epithelial folds at segment boundaries during the late stages of Drosophila embryogenesis. We found that the fold formation at the segment boundaries occurs through the juxtaposition of two key morphogenetic processes: local apical constriction and tissue-level compressive forces from posterior segments. Further, we found that epidermal spreading and fold formation are accompanied by spatiotemporal pulses of Hedgehog (Hh) signaling. A computational model that incorporates the local forces generated from the differential tensions of the apical, basal, and lateral sides of the cell and active forces generated within the whole tissue recapitulates the overall fold formation process in wild-type and Hh overexpression conditions. In sum, this work demonstrates how epithelial folding depends on multiple, separable physical mechanisms to generate the final morphology of the dorsal epidermis. This work illustrates the modularity of morphogenetic unit operations that occur during epithelial morphogenesis.

上皮折叠是一个基本的形态发生过程，它将平面上皮片材塑造成复杂的三维结构。多种机制可以产生上皮皱襞，包括在细胞水平局部起作用的顶端收缩、组织尺度上的差异生长，或由于邻近组织的压缩而弯曲。在这里，我们研究了果蝇晚期在节段边界处形成背侧上皮褶皱。胚胎发生。我们发现节段边界处的褶皱形成是通过两个关键形态发生过程的并置发生的：局部顶端收缩和来自后节的组织水平压缩力。此外，我们发现表皮扩散和褶皱形成伴随着刺猬（Hh）信号的时空脉冲。一个计算模型结合了由细胞的顶端、基底和侧面的不同张力产生的局部力和在整个​​组织内产生的主动力，概括了野生型和 Hh 过表达条件下的整体褶皱形成过程。总之，这项工作证明了上皮折叠如何依赖于多种可分离的物理机制来产生背侧表皮的最终形态。