The assembly and function of cellular contractile systems

1)背景和我们理解的关键差距。细胞力的产生驱动着 真核生物的细胞分裂、细胞迁移和肌肉收缩。因此， 细胞力的产生对发育生物学和力依赖性的发展都是至关重要的。 比如癌症细胞通过组装细胞收缩系统产生力。收缩系统 从更大的分子组装体中的单个组分的集体作用中产生。我们的第一 对细胞收缩系统的研究集中在负责产生收缩的分子马达的类别上。 收缩力，肌球蛋白II。肌球蛋白II的力量产生形式是一种细丝。给定的肌球蛋白II丝可以 含有多种不同的肌球蛋白II旁系同源物（即，异丝），其中每个单独的肌球蛋白II特异性地具有 独特的生物物理特性。以前，含有肌球蛋白II的异丝的特异性功能， 收缩系统未知。我们在ESI MIRA资助期间的工作揭示了以下方面的多重角色： 在细胞分裂和肌肉收缩的背景下，未来的工作应该解决如何异性恋- 纤维被调节，影响机械输出，并与其他收缩系统成分合作。 2)主要研究者对近期进展的描述。在非肌肉细胞中，我们报道了异丝 多种功能。肌球蛋白IIA丝在间期和间期都为肌球蛋白IIB丝的形成提供了种子。 有丝分裂/胞质分裂（Festival et al. 2016，Taneja et al.，2020年）。肌球蛋白IIA在异丝驱动中的存在 皮质张力（Taneja et al. 2020），并受肌球蛋白IIA转换和肌球蛋白IIA磷酸化的调节。 肌球蛋白IIA调节轻链（Taneja和Burnette 2019，Taneja等人2021）。与此同时， 异丝中的肌球蛋白IIB在有丝分裂/胞质分裂期间稳定细胞皮质并调节细胞动力学 通过多种机制实现保真度（Taneja et al. 2020）。在心肌细胞内，我们报告说， NMIIA/NMIIB异丝为肌特异性肌球蛋白Parkinson，β肌球蛋白II的丝提供种子， 只存在于称为肌肉应力纤维的肌节前体中。我们还通过实验证明了 肌肉应力纤维直接引起肌节（Festival et al. 2018，Taneja，Neininger et al. 2020）。第三章 展望未来的研究计划。在这里，我们建议在ESI MIRA的研究结果的基础上， 采取针对三个领域的多方面方法：A）我们将继续阐明特定分子如何 肌球蛋白II丝的组分，以及其他收缩系统蛋白质如α-辅肌动蛋白和formins的组分， 调节细胞力的产生。B）我们将确定非-- 肌肉和肌球蛋白II，α-辅肌动蛋白，和潜在的其他肌节蛋白的肌肉旁系同源物， 肌节形成和有丝分裂/胞质分裂（我们发现一些肌肉旁系同源物从肌节中重新定位， 在细胞分裂期间肌节到皮层）。C）最后，我们将使用斑马鱼胚胎来验证假设 这些都是从我们的体外实验中得出的。

1) Background and key gaps in our understanding. Cellular force generation drives processes vital for eukaryotic life, including cell division, cell migration, and muscle contraction. Thus, the basic principles underlying cellular force generation are central to both developmental biology and the progression of force-dependent diseases like cancer. Cells generate force by assembling cellular contractile systems. Contractile systems emerge from the collective action of individual components within a larger molecular assembly. Our first investigation into cellular contractile systems focused on the class of molecular motors responsible for generating contractile forces, myosin II. The force-generating form of myosin II is a filament. A given myosin II filament can contain multiple, distinct myosin II paralogs (i.e., hetero-filaments), wherein each individual myosin II paralog has unique biophysical properties. Previously, the specific function(s) of myosin II-containing hetero-filaments within contractile systems was unknown. Our work during the ESI MIRA funding period has revealed multiple roles for hetero-filaments in the context of cell division and muscle contraction. Future work should address how hetero- filaments are regulated, influence mechanical output, and cooperate with other contractile system components. 2) Description of recent progress by the PI. In non-muscle cells, we reported that hetero-filaments serve multiple functions. Myosin IIA filaments seed the formation of myosin IIB filaments in both interphase and mitosis/cytokinesis (Fenix et al. 2016, Taneja et al., 2020). The presence of myosin IIA in hetero-filaments drives cortex tension (Taneja et al. 2020) and is regulated by both myosin IIA turnover and by phosphorylation of the myosin IIA regulatory light chain (Taneja and Burnette 2019, Taneja et al. 2021). Meanwhile, the presence of myosin IIB in hetero-filaments stabilizes the cell cortex during mitosis/cytokinesis and regulates cytokinetic fidelity through multiple mechanisms (Taneja et al. 2020). Within cardiac muscle cells, we reported that NMIIA/NMIIB hetero-filaments seed filaments of the muscle-specific myosin paralog, β myosin II, and are found exclusively in the sarcomere precursors known as muscle stress fibers. We also experimentally demonstrated that muscle stress fibers directly give rise to sarcomeres (Fenix et al. 2018, Taneja, Neininger et al. 2020). 3) Overview of future research program. Here, we propose to build upon our findings from the ESI MIRA by taking a multi-faceted approach aimed at three areas: A) We will continue elucidating how specific molecular components of myosin II filaments, as well as those of other contractile system proteins like α-actinin and formins, regulate cellular force production. B) We will determine the roles, and specific differences in function, of the non- muscle and muscle paralogs of myosin II, α-actinin, and potentially other sarcomeric proteins during both sarcomere formation and mitosis/cytokinesis (we have found that some muscle paralogs re-localize from the sarcomere to the cortex during cell division). C) Finally, we will use zebrafish embryos to test the hypotheses that come out of our in vitro experiments in vivo.