Coravos Jonathan S, Martin Adam C
Department of Biology, Massachusetts Institute of Technology, 31 Ames Street, Cambridge, MA 02142, USA.
Department of Biology, Massachusetts Institute of Technology, 31 Ames Street, Cambridge, MA 02142, USA.
Dev Cell. 2016 Nov 7;39(3):346-358. doi: 10.1016/j.devcel.2016.09.023. Epub 2016 Oct 20.
Actomyosin networks generate contractile force that changes cell and tissue shape. In muscle cells, actin filaments and myosin II appear in a polarized structure called a sarcomere, in which myosin II is localized in the center. Nonmuscle cortical actomyosin networks are thought to contract when nonmuscle myosin II (myosin) is activated throughout a mixed-polarity actin network. Here, we identified a mutant version of the myosin-activating kinase, ROCK, that localizes diffusely, rather than centrally, in epithelial cell apices. Surprisingly, this mutant inhibits constriction, suggesting that centrally localized apical ROCK/myosin activity promotes contraction. We determined actin cytoskeletal polarity by developing a barbed end incorporation assay for Drosophila embryos, which revealed barbed end enrichment at junctions. Our results demonstrate that epithelial cells contract with a spatially organized apical actomyosin cortex, involving a polarized actin cytoskeleton and centrally positioned myosin, with cell-scale order that resembles a muscle sarcomere.
肌动球蛋白网络产生收缩力，可改变细胞和组织的形状。在肌肉细胞中，肌动蛋白丝和肌球蛋白II以一种称为肌节的极化结构出现，其中肌球蛋白II位于中心位置。非肌肉皮质肌动球蛋白网络被认为在非肌肉肌球蛋白II（肌球蛋白）在混合极性肌动蛋白网络中被激活时发生收缩。在这里，我们鉴定出了肌球蛋白激活激酶ROCK的一个突变版本，它在上皮细胞顶端呈弥散分布，而非集中分布在中心位置。令人惊讶的是，这种突变会抑制收缩，这表明顶端集中定位的ROCK/肌球蛋白活性会促进收缩。我们通过开发一种针对果蝇胚胎的带刺末端掺入测定法来确定肌动蛋白细胞骨架的极性，该测定法揭示了连接处带刺末端的富集。我们的结果表明，上皮细胞通过空间组织化的顶端肌动球蛋白皮质收缩，涉及极化的肌动蛋白细胞骨架和位于中心位置的肌球蛋白，其细胞尺度的有序性类似于肌肉肌节。
