The Role of Non-Cell Autonomous Wnt Activation in Hair Follicle Growth and Cancer

描述（由申请人提供）：组织稳态和再生由多种细胞类型的协调生长介导，以产生维持生物体完整性和功能的组织。这种持久再生组织的能力依赖于成体干细胞， 栖息在一个称为生态位的特殊环境中，影响着它们的自我更新、生长和分化。不能维持或动员干细胞会导致组织损失和功能障碍，而这些细胞的不受控制的激活会助长无组织的生长和癌症。阐明关键分子信号如何控制干细胞行为对设计治疗人类疾病的靶向疗法具有巨大意义。研究哺乳动物干细胞是如何被调控的一个主要挑战是传统的静态分析无法随着时间的推移跟踪体内细胞群的命运和行为。该提案旨在解决我们对信号如何参与未分化细胞群体以产生稳健和有组织生长的知识中的一个主要空白。具体而言，尚不清楚（1）在再生过程中，细胞行为如细胞分裂和运动是由关键形态发生信号调节的，（2）这些信号如何在整个细胞场中传播以确保稳健但区室化的生长，以及（3）这些机制如何在肿瘤发生期间促成无序和不受控制的生长。毛囊是解决这些问题的理想模型，因为它非常容易获得，并且以依赖于常驻干细胞的方式经历了良好的周期性再生。通过将该模型与一种新的实时成像技术相结合，我们现在可以独特地解决这些悬而未决的问题。在这个项目中，我们研究了Wnt/β-catenin信号传导，毛囊再生所需的关键分子途径，如何在整个未分化细胞群体中传播，以促进同步和协调的生长。通过活体成像，我们发现，仅需要一部分细胞来促进该信号的非细胞自主激活和整个周围上皮细胞的生长行为，并且与可扩散Wnt配体的上调相关。我们的第一个目标是使用体外细胞培养和遗传小鼠模型，在存在或不存在Wnt分泌的情况下激活β-连环蛋白，以确定促进毛囊再生对Wnt配体分泌的需求。第二个检查Wnt分泌是否需要在基底细胞癌（BCC），最常见的人类皮肤癌，这是依赖于Wnt信号的生长上皮Wnt激活。我们还将确定持续的上皮Wnt信号传导如何影响间充质以调节BCC生长，使用组织移植和遗传方法来调节BCC小鼠模型中的上皮和真皮Wnt活化。实现这些目标将为确保适当组织再生的原理机制以及如何利用它们来促进癌症的集体生长提供新的见解。

DESCRIPTION (provided by applicant): Tissue homeostasis and regeneration are mediated by the coordinated growth of multiple cell types to generate tissue that sustains integrity and function of the organism. This ability to durably regenerate tissue relies on adult stem cells that reside in a specialized environment called the niche, which influences their self- renewal, growth and differentiation. Failure to maintain or mobilize stem cells results in tissue loss and dysfunction, while uncontrolled activation of these cells can fuel disorganized growth and cancer. Elucidating how key molecular signals govern stem cell behavior holds tremendous implications for designing targeted therapies to treat human diseases. A major challenge to examining how mammalian stem cells are regulated is the inability of conventional static analysis to follow the fate and behavior of cell populations in vivo over time. This proposal aims to address a major gap in our knowledge of how signals can engage a population of undifferentiated cells to yield robust and organized growth. In particular, is still unclear (1) wht cellular behaviors such as cell divisions and movement are regulated by key morphogenetic signals during regeneration, (2) how these signals are disseminated throughout a field of cells in to ensure robust but compartmentalized growth, and (3) how these mechanisms can contribute to disorganized and uncontrolled growth during tumorigenesis. The hair follicle is the ideal model to address these questions as it is exceptionally accessible and undergoes well-characterized cyclical regeneration in a manner dependent on resident stem cells. By coupling this model to a novel live imaging technique we are now uniquely poised to address these outstanding questions. In this project, we examine how Wnt/�-catenin signaling, a key molecular pathway required for hair follicle regeneration, is propagated throughout a population of undifferentiated cells to promote synchronous and coordinated growth. By live imaging, we have found that only a subset of cells is required to fuel the non-cell autonomous activation of this signal and growth behaviors throughout surrounding epithelial cells and is associated with upregulation of diffusible Wnt ligands. Our first aim uses both in vitro cell culture and genetic mouse models that activate �-catenin in the presence or absence of Wnt secretion to determine the requirement for Wnt ligand secretion in promoting hair follicle regeneration. The second examines if Wnt secretion is required for epithelial Wnt activation in basal cell carcinomas (BCCs), the most common human skin cancer, which is dependent upon Wnt signaling for growth. We will also determine how sustained epithelial Wnt signaling can influence the mesenchyme to regulate BCC growth, using tissue grafting and genetic approaches to modulate epithelial and dermal Wnt activation in a BCC mouse model. Accomplishing these aims will provide novel insight into the principle mechanisms that ensure proper tissue regeneration and how they can also be exploited deleteriously to promote collective growth in cancer.