Actin Organization and Polarization

描述（由申请人提供）：神经冲动的传递、胚胎发育、分子在上皮层的运输、正常细胞和转移细胞的细胞迁移以及细胞分裂都需要细胞不对称的产生。细胞骨架在这些过程中起着至关重要的作用，作为细胞内和细胞运动的力发生器，稳定不对称细胞结构的支架，以及定向细胞内运动的轨道。了解细胞极性建立过程中细胞骨架组织的重要线索来自于我们对活酵母细胞中肌动蛋白动力学的研究。我们发现肌动蛋白斑块和索是酵母肌动蛋白细胞骨架的主要组成部分，通过在极化细胞表面生长的位点组装来实现极化，并且在肌动蛋白索的情况下，沿着母芽轴延伸。此外，我们还获得了肌球蛋白I蛋白在这一过程中所起作用的证据。肌球蛋白I蛋白是在25年前被发现的。然而，许多这些蛋白质的功能是未知的，关于肌球蛋白功能和作用的有限证据也没有提供关于它们的作用机制的信息。在出芽酵母中，有两个功能冗余的肌球蛋白I基因，MYO3和MYO5。这两个基因的缺失会导致肌动蛋白索和肌动蛋白斑块的紊乱，并导致肌动蛋白依赖过程的缺陷，包括分泌、内吞作用和极化细胞生长和分裂。与此一致的是，我们和其他人发现1)肌凝蛋白I蛋白定位于极化细胞表面生长的0位点，2)verprolin和Las17p/Bee1p，一种激活Arp2/3复合物的肌动蛋白成核活性的蛋白，与肌凝蛋白I蛋白结合，并有助于肌凝蛋白I蛋白靶向极化细胞表面生长的位点，3)肌凝蛋白I蛋白可以结合并激活Arp2/3复合物。未来对肌动蛋白I介导的肌动蛋白组装机制的研究将集中在肌动蛋白电缆和贴片之间的关系，肌动蛋白电缆和贴片组装和拆卸的机制，以及肌动蛋白I蛋白和其他细胞骨架组织者在肌动蛋白细胞骨架的组装、拆卸和动力学中的作用。考虑到肌动蛋白细胞骨架在建立细胞极性中的基本作用，以及肌动蛋白I蛋白在肌动蛋白成核和基于肌动蛋白的运动中的作用的证据，令人惊讶的是，我们对肌动蛋白的功能及其在肌动蛋白细胞骨架组织中的确切作用知之甚少。提出的研究旨在填补这一空白。

DESCRIPTION (provided by applicant): Generation of cellular asymmetry is required for transmission of nerve impulses, embryonic development, transport of molecules across an epithelial layer, cell migration in normal and metastatic cells, and cell division. The cytoskeleton plays an essential role in these processes as a force generator for intracellular and cellular movement, a scaffold to stabilize asymmetric cell structure, and a track for directed intracellular movement. An important clue to understanding cytoskeletal organization during establishment of cell polarity came from our studies on actin dynamics in living yeast cells. We find that actin patches and cables, the major components of the actin cytoskeleton in yeast, achieve polarization by assembly at sites of polarized cell surface growth, and in the case of actin cables, extension along the mother-bud axis. Moreover, we obtained evidence for a role of myosin I proteins in this process. Myosin I proteins were discovered over 25 years ago. Nonetheless, the functions of many of these proteins are unknown, and the limited evidence for myosin function and roles provides no information on their mechanism of action. In the budding yeast, there are two functionally redundant myosin I genes, MYO3 and MYO5. Deletion of both genes produces disorganization of actin cables and actin patches, and defects in actin-dependent processes including secretion, endocytosis, and polarized cell growth and division. Consistent with this, we and others find that 1) myosin I proteins localize to sites 0 polarized cell surface growth, 2) verprolin and Las17p/Bee1p, a protein that activates the actin nucleation activity of the Arp2/3 complex, bind to myosin I proteins and contribute to targeting of myosin I proteins to sites of polarized cell surface growth, and 3) myosin I proteins can bind to and activate the Arp2/3 complex. Future studies on the mechanism of my osin I-mediated actin assembly will focus on the relation between actin cables and patches, the mechanism underlying actin cable and patch assembly and disassembly, and the role for myosin I proteins and other cytoskeletal organizers in assembly, disassembly and dynamics of the actin cytoskeleton. Given the fundamental role of the actin cytoskeleton in establishment of cell polarity, and evidence for a role of myosin I proteins in actin nucleation and actin-based movement, it is surprising that we know so little regarding the function of myosins and their precise role in actin cytoskeletal organization. The studies proposed are designed to fill that gap.