Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1583, USA.
Proc Natl Acad Sci U S A. 2010 Aug 17;107(33):14645-50. doi: 10.1073/pnas.1004023107. Epub 2010 Aug 2.
Nonmuscle myosins (NMs) II-A and II-B are essential for embryonic mouse development, but their specific roles are not completely defined. Here we examine the isoforms and their domain specifically in vivo and in vitro by studying mice and cells in which nonmuscle myosin heavy chain (NMHC) II-A is genetically replaced by NMHC II-B or chimeric NMHC IIs that exchange the rod and head domains of NM II-A and II-B. In contrast with the failure of visceral endoderm formation resulting in embryonic day (E)6.5 lethality of A(-)/A(-) mice, replacement with NM II-B or chimeric NM IIs restores a normal visceral endoderm. This finding is consistent with NM II's role in cell adhesion and also confirms an essential, isoform-independent requirement for NM II in visceral endoderm function. The knock-in mice die between E9.5 and 12.5 because of defects in placenta formation associated with abnormal angiogenesis and cell migration, revealing a unique function for NM II-A in placenta development. In vitro results further support a requirement for NM II-A in directed cell migration and focal adhesion formation. These findings demonstrate an isoform-specific role for NM II-A during these processes, making replacement by another isoform, or chimeric NM II isoforms, less successful. The failure of these substitutions is not only related to the different kinetic properties of NM II-A and II-B, but also to their subcellular localization determined by the C-terminal domain. These results highlight the functions of the N-terminal motor and C-terminal rod domains of NM II and their different roles in cell-cell and cell-matrix adhesion.
非肌肉肌球蛋白（NM）II-A 和 II-B 对于胚胎期的小鼠发育至关重要，但它们的具体作用尚未完全明确。在此，我们通过研究 NMHC II-A 基因被 NMHC II-B 或肌球蛋白 II 重链同型嵌合体取代的小鼠和细胞，从体内和体外来研究这些同工型及其结构域。与 A(-)/A(-) 小鼠由于内脏内胚层形成失败导致胚胎期 6.5 天（E6.5）致死的情况相反，用 NM II-B 或嵌合 NM II 取代可恢复正常的内脏内胚层。这一发现与 NM II 在细胞黏附中的作用一致，也证实了 NM II 在维持内脏内胚层功能方面具有独立于同工型的关键作用。敲入小鼠因胎盘形成缺陷而在 E9.5 至 12.5 天之间死亡，这些缺陷与异常血管生成和细胞迁移有关，这揭示了 NM II-A 在胎盘发育中的独特作用。体外结果进一步支持了 NM II-A 在定向细胞迁移和焦点黏附形成中的需求。这些发现表明 NM II-A 在这些过程中具有同工型特异性的作用，因此另一种同工型或嵌合 NM II 同工型的取代不太成功。这些取代的失败不仅与 NM II-A 和 II-B 的不同动力学特性有关，还与它们由 C 端结构域决定的亚细胞定位有关。这些结果突出了 NM II 的 N 端运动和 C 端杆状结构域的功能及其在细胞-细胞和细胞-基质黏附中的不同作用。
