Regulation of intestinal tissue homeostasis by the transcription factor Escargot

 描述（申请人提供）：所有生物体的一个显著特征是它们能够适应周围环境的变化，在细胞和组织水平上观察到类似程度的可塑性。在成年果蝇的肠道中，肠道干细胞（ISCs）增殖和分化以维持组成该器官的吸收细胞和分泌细胞的群体。然而，增殖和分化之间的平衡被外部损伤如损伤、炎症或老化所打破，导致干细胞的不受控制的增殖、维持干细胞和分化细胞的标志的错误分化细胞的积累以及组织屏障完整性的丧失。一 错误分化的细胞的特征是转录因子Escargot（Esg）的表达，其在健康果蝇中的表达通常限于ISC及其直接子代成肠细胞（EB）。Esg是转录因子Snail家族的成员，其通过调节上皮-间充质转化（EMT）而在发育以及癌症起始和转移中发挥作用。脊椎动物Snail的保守靶点包括细胞-细胞粘附分子，如上皮钙粘蛋白（E-Cadherin）。在果蝇中，位于吸收性肠上皮细胞（EC）和肠内分泌细胞（EE）之间的隔膜连接（SJs）是脊椎动物紧密连接（TJs）的类似物，调节肠道中的细胞间流量，并且是维持正常肠道稳态所必需的。肠中受损的SJS与肠的顶端和基底上皮表面之间的渗透性增加以及肠屏障功能丧失相关。在果蝇中，Esg是必需的ISCs FR维护和EB介导的分化决定：损失的esg的结果偏向分泌EE谱系。有趣的是，大约一半的已知编码SJ组件的基因已被确定为推定的直接抑制Esg的目标，从一个修改的染色质结合试验，检测基因组中的Esg结合区域，并从转录组分析排序的ISC/EB与不同的esg表达。因此，这一提议的中心假设是，肠内ESG对损伤或年龄反应的错误表达改变了细胞间连接的组织，从而破坏了肠组织的稳态。该研究通过以下具体目标来验证这一假设：SA 1）确定esg表达在衰老和应激反应中变化的机制。SA 2）阐明果蝇肠道Esg蛋白与隔连接蛋白的关系。这些研究将有助于了解肠道组织的稳态是如何维持与蜗牛家族转录因子Esg调控的关键转录程序的长期目标，并扩大我们对蜗牛家族影响组织稳态，影响器官功能和驱动肿瘤发生的机制的了解。

 DESCRIPTION (provided by applicant): A remarkable trait of all organisms is their ability to adjust to the changes in the surrounding environment, and a similar degree of plasticity is observed at the levels of cells and tissues. In the intestine of adult Drosophila melanogaster, intestinal stem cells (ISCs) proliferate and differentiate to maintain the populations of absorptiv and secretory cells that comprise the organ. However, the balance between proliferation and differentiation is tipped by external insults such as damage, inflammation, or aging, resulting in an uncontrolled proliferation of stem cells, an accumulation of mis-differentiated cells that maintain hallmarks of both stem and differentiated cells, and a loss of tissue barrier integrity. A signature feature of the mis-differentiated cells is the expression of the transcription factor Escargot (Esg), whose expression in healthy flies is typically limited to ISCs and their immediate daughters, enteroblasts (EBs). Esg is a member of the Snail family of transcription factors that are well-known for roles in development, as well as cancer initiation and metastasis, by regulating epithelial-mesenchymal transitions (EMT). Conserved targets of vertebrate Snail include cell-cell adhesion molecules, such as epithelial cadherin (E-Cadherin). Septate junctions (SJs), the Drosophila analog of vertebrate tight junctions (TJs), between absorptive enterocytes (ECs) and enteroendocrine (EE) cells regulate paracellular flux in the intestine and are required for the maintenance of normal intestinal homeostasis. Compromised SJs in the intestine correlate with increased permeability between the apical and basal epithelial surfaces of the intestine, as well as loss of intestinal barrier function. In Drosophila, Esg is required in ISCs fr maintenance and in EBs to mediate differentiation decisions: loss of esg results in a bias toward the secretory EE lineage. Interestingly, roughly half of the genes known to encode SJ components have been identified as putative direct repression targets of Esg, from a modified chromatic binding assay that detects Esg-binding regions in the genome and from transcriptome analyses of sorted ISC/EBs with varied esg expression. Therefore, the central hypothesis of this proposal is that mis- expression of esg in the intestine in response to damage or age alters the organization of intercellular junctions to disrupt intestinal tissue homeostasis. The proposed study examines this hypothesis through the following specific aims: SA 1) To determine the mechanisms by which esg expression changes in response to aging and stress. SA 2) To elucidate the relationship between Esg and septate junction proteins in the Drosophila intestine. These studies will contribute to the long-term objective in understanding how intestinal tissue homeostasis is maintained with regard to a key transcription program regulated by the Snail family transcription factor Esg and expand our knowledge in the mechanisms by the Snail family can influence tissue homeostasis, impact organ function, and drive tumorigenesis.