Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213, USA.
Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213, USA; Department of Developmental Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA; Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Curr Biol. 2017 May 8;27(9):1326-1335. doi: 10.1016/j.cub.2017.03.065. Epub 2017 Apr 20.
During early cardiogenesis, bilateral fields of mesenchymal heart progenitor cells (HPCs) move from the anterior lateral plate mesoderm to the ventral midline, undergoing a mesenchymal-to-epithelial transition (MET) en route to forming a single epithelial sheet. Through tracking of tissue-level deformations in the heart-forming region (HFR) as well as movement trajectories and traction generation of individual HPCs, we find that the onset of MET correlates with a peak in mechanical stress within the HFR and changes in HPC migratory behaviors. Small-molecule inhibitors targeting actomyosin contractility reveal a temporally specific requirement of bulk tissue compliance to regulate heart development and MET. Targeting mutant constructs to modulate contractility and compliance in the underlying endoderm, we find that MET in HPCs can be accelerated in response to microenvironmental stiffening and can be inhibited by softening. To test whether MET in HPCs was responsive to purely physical mechanical cues, we mimicked a high-stress state by injecting an inert oil droplet to generate high strain in the HFR, demonstrating that exogenously applied stress was sufficient to drive MET. MET-induced defects in anatomy result in defined functional lesions in the larval heart, implicating mechanical signaling and MET in the etiology of congenital heart defects. From this integrated analysis of HPC polarity and mechanics, we propose that normal heart development requires bilateral HPCs to undergo a critical behavioral and phenotypic transition on their way to the ventral midline, and that this transition is driven in response to the changing mechanical properties of their endoderm substrate.
在心脏发生的早期，双侧间质心脏祖细胞 (HPC) 从前侧板中胚层向腹侧中线上迁移，在这个过程中经历了间质到上皮的转变 (MET)，最终形成单层上皮细胞。通过跟踪心脏形成区域 (HFR) 的组织水平变形以及单个 HPC 的运动轨迹和牵引力产生，我们发现 MET 的发生与 HFR 内机械应力的峰值以及 HPC 迁移行为的变化有关。针对肌动球蛋白收缩性的小分子抑制剂表明，组织整体顺应性的时间特异性要求可调节心脏发育和 MET。通过靶向突变构建来调节下胚层的收缩性和顺应性，我们发现 HPC 中的 MET 可以响应微环境变硬而加速，并且可以通过软化来抑制。为了测试 HPC 中的 MET 是否对纯粹的物理机械线索有反应，我们通过注射惰性油滴在 HFR 中产生高应变来模拟高应力状态，证明外源性施加的应力足以驱动 MET。MET 引起的解剖缺陷导致幼虫心脏出现明确的功能损伤，这表明机械信号和 MET 参与了先天性心脏缺陷的病因。从 HPC 极性和力学的综合分析中，我们提出正常心脏发育需要双侧 HPC 在向腹侧中线迁移的过程中经历关键的行为和表型转变，并且这种转变是对其下胚层基质机械特性变化的响应。
