Formation of epithelia through mesenchymal-epithelial transition (MET) is essential for embryonic development and for many physiological and pathological processes. This study investigates MET in vivo in the chick embryo lateral mesoderm, where a multilayered mesenchyme transforms into two parallel epithelial sheets that constitute the coelomic lining of the embryonic body cavity. Prior to MET initiation, mesenchymal cells exhibit non-polarized distribution of multiple polarity markers, albeit not aPKC. We identified an epithelializing wave that sweeps across the lateral mesoderm, the wavefront of which is characterized by the accumulation of basal fibronectin and a network of 3D rosettes composed of polarized, wedge-shaped cells surrounding a central focus of apical markers, now including aPKC. Initiation of the MET process is dependent on extracellular matrix-integrin signaling acting through focal adhesion kinase and talin, whereas progression through the rosette phase requires aPKC function. We present a stepwise model for MET, comprising polarization, 3D-rosette, and epithelialization stages.

通过间充质-上皮转化（MET）形成上皮细胞对于胚胎发育以及许多生理和病理过程至关重要。本研究调查体内MET在鸡胚外侧中胚层中，多层间质转化为两个平行的上皮片，构成胚胎体腔的体腔内层。在 MET 启动之前，间充质细胞表现出多个极性标记的非极化分布，尽管不是 aPKC。我们发现了一个扫过外侧中胚层的上皮化波，其波前的特征是基底纤连蛋白的积累和由极化的楔形细胞组成的 3D 玫瑰花结网络，围绕着顶端标记的中心焦点，现在包括 aPKC。MET 过程的启动依赖于通过粘着斑激酶和talin 起作用的细胞外基质整合素信号传导，而玫瑰花结阶段的进展需要 aPKC 功能。我们提出了 MET 的逐步模型，