The body axis of vertebrates is subdivided into repetitive compartments called somites, which give rise primarily to the segmented architecture of the musculoskeletal system in the adult body. Somites form in a sequential and rhythmic manner in embryos and a physical boundary separates each somite from the rest of the unsegmented tissue and adjoining somites. Precise positioning of somite boundaries and determination of boundary cell fate in a select group of cells is thought to be driven by gene expression patterns and morphogen gradients. This pre-patterning step is followed by a mechanical process involving actomyosin activation in boundary cells and formation of an extracellular matrix that results in morphological boundary formation. While genes involved in somite boundary formation have been identified, there are many open questions about the underlying pre-patterning dynamics and mechanics and how these processes are coupled to generate a morphological boundary. Here, focusing on segmentation of zebrafish embryos as a model, we review pre-patterning processes critical for boundary formation and how cytoskeletal activity drives tissue separation. Our outlook is that this system holds exciting new avenues for unearthing general principles of boundary formation in developing embryos.

脊椎动物的身体轴被细分为称为体节的重复区室，它们主要产生成体肌肉骨骼系统的分段结构。体节在胚胎中以连续和有节奏的方式形成，物理边界将每个体节与其余未分割的组织和相邻的体节分开。体节边界的精确定位和选定细胞组中边界细胞命运的确定被认为是由基因表达模式和形态发生素梯度驱动的。此预图案化步骤之后是机械过程，涉及边界细胞中的肌动球蛋白活化和导致形态边界形成的细胞外基质的形成。虽然已经确定了参与体节边界形成的基因，关于潜在的预图案动力学和力学以及这些过程如何耦合以生成形态边界，存在许多悬而未决的问题。在这里，我们以斑马鱼胚胎的分割为模型，回顾了对边界形成至关重要的预图案化过程以及细胞骨架活动如何驱动组织分离。我们的前景是，该系统为发掘胚胎发育中边界形成的一般原则提供了令人兴奋的新途径。