Polarity complexes in cellular differentiation

我的实验室的一个基本目标是了解细胞极性，特别是神经元极性的潜在机制。使用极化上皮细胞的工作已经证实，存在三个保守的核心蛋白质-蛋白质复合体，并且在一定程度上通过调节河马信号通路的活性来建立细胞极性。尽管有文献表明，河马信号在非神经细胞中控制细胞生长并调节细胞机械转导，但对河马信号在有丝分裂后神经元中的作用知之甚少。我们由NSERC资助的项目专注于在中枢神经系统组织中识别新的极性复合体，以及这些复合体如何发挥作用来控制神经元的极性。我们最近的工作揭示了河马蛋白激酶--大肿瘤抑制蛋白1(LATS1)在稳定正在发育的突触中的新功能。在非神经细胞中，LATS1和相关蛋白LATS2在驱动河马信号方面的功能相似。然而，这两种蛋白的显著差异表明，它们可能对不同的细胞内信号通路起作用。我们的初步数据显示，在发育中的神经系统中，LATS1和LATS2具有相反的表达谱，这意味着LATS2在成熟的中枢神经系统中的表达。我们的初步数据还显示，LATS2富含树突棘，并影响肌动蛋白的周转和突触的形态。基于这些有趣的发现，我们的目标是确定保守的河马蛋白激酶LATS2通过调节突触结构可塑性来影响神经元功能的机制。特别是，我们将：1)定义LATS2在神经元极性和突触形态中的作用。我们将描述LATS2是如何被招募到兴奋性突触的，并确定其对脊柱形态的影响是否依赖于激酶。我们还将评估LATS2对正常认知的重要性。2)研究LATS2激酶活性如何调节肌动蛋白动态，从而调节树突棘的形态。我们将确定LATS2是直接影响肌动蛋白动力学，还是通过调节小肌动蛋白调节RhoGTP酶、Rac、Rho或CDC42的活性来实现。3)确定LATS2上游调控突触形态的分子途径。我们将测试其他已知的LATS2相关蛋白Kibra和Merlin是否影响LATS2对突触稳定性的活性依赖调节。总之，这项工作是新颖的，因为还没有关于保守的LATS激酶在有丝分裂后神经元中的作用的描述。此外，这项工作将提供对河马信号成分在调节神经元极性中所扮演的角色的机械性洞察，包括这些信号成分如何对突触形态和功能的调节做出贡献。

A fundamental aim of my laboratory is to understand the underlying mechanisms of cellular polarity and in particular neuronal polarity. Work using polarized epithelial cells has established that three conserved core protein-protein complexes exist and are important for establishing cellular polarity in part by regulating the activity of the Hippo signaling pathway. Despite an emerging literature revealing that Hippo signaling controls cell growth and modulates cellular mechanotrasduction in non-neuronal cells, little is known about the role for Hippo signaling components in post mitotic neurons. Our NSERC funded program has focused on identifying novel polarity complexes in CNS tissues and how these function to control neuronal polarity. Our recent work has revealed a novel function for the Hippo kinase, large tumour suppressor kinase 1 (LATS1) in the stabilization of developing synapses. In non-neuronal cells, LATS1 and a related protein LATS2 function similarly in driving Hippo signaling. However, significant differences in these two proteins suggest they likely contribute to different intracellular signaling pathways. Our preliminary data reveals that in the developing nervous system, LATS1 and LATS2 have opposite expression profiles implicating LATS2 in the mature CNS. Our preliminary data also reveals that LATS2 is enriched in dendritic spines and affects both actin turnover and synapse morphology. Building on these intriguing findings, we aim to identify mechanisms by which the conserved Hippo kinase LATS2 contributes to the regulation of synaptic structural plasticity to affect neuronal function. In particular, we will: 1) Define a role for LATS2 in neuronal polarity and synaptic morphology. We will characterize how LATS2 is recruited to excitatory synapses and determine if the effects on spine morphology are kinase dependant. We will also assess the importance of LATS2 for normal cognition. 2) Characterize how LATS2 kinase activity regulates actin dynamics to regulate dendritic spine morphology. We will determine whether LATS2 directly affects actin dynamics or does so by regulating the activity of the small actin regulatory RhoGTPases, Rac, Rho or Cdc42. 3) Identify molecular pathways that function upstream of LATS2 to regulate synaptic morphology. We will test whether other known LATS2 associating proteins, KIBRA and Merlin, affect activity dependent regulation of LATS2 contributing to synapse stability.  Together this work is novel, as there have been no descriptions for the contributions of the conserved LATS kinases in post mitotic neurons. Further this work will provide mechanistic insight into the role Hippo signaling components play in regulating neuronal polarity including how these signaling components contribute to the regulation of synaptic morphology and function.