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，以维持组成器官的吸收细胞和分泌细胞的数量。然而，增殖和分化之间的平衡被外部因素打破，如损伤、炎症或衰老，导致干细胞不受控制的增殖，错误分化的细胞积累，保持干细胞和分化细胞的特征，以及组织屏障完整性的丧失。一个 错误分化细胞的标志性特征是转录因子ESCARGET(ESG)的表达，该转录因子在健康果蝇中的表达通常仅限于ISCs及其直系子代成肠母细胞(EBS)。ESG是Snail转录因子家族中的一员，通过调节上皮-间充质转化(EMT)，在发育以及癌症的起始和转移中扮演着重要角色。脊椎动物蜗牛的保守靶标包括细胞与细胞间的黏附分子，如上皮钙粘附素(E-Caherin)。分隔连接(SJS)是一种类似于果蝇的脊椎动物紧密连接(TJs)，位于吸收肠细胞(ECs)和肠内分泌(EE)细胞之间，调节肠道中的细胞旁流量，是维持正常肠道内平衡所必需的。肠道SJS受损与肠道顶端和底部上皮表面之间的通透性增加以及肠道屏障功能丧失有关。在果蝇中，ESG在ISCs的维持和EBS中是必需的，以调节分化决定：ESG的丢失导致对分泌型EE谱系的偏见。有趣的是，大约一半已知的编码SJ组分的基因已经被鉴定为ESG的直接抑制靶标，这是通过一种改进的检测基因组中ESG结合区的显色结合试验以及从具有不同ESG表达的已分类ISC/EBS的转录组分析中确定的。因此，这一建议的中心假设是，ESG在肠道中的错误表达对损伤或年龄的反应改变了细胞间连接的组织，从而破坏了肠道组织的动态平衡。这项拟议的研究通过以下具体目标来检验这一假说：SA 1)确定ESG表达随着年龄和压力的反应而变化的机制。Sa 2)阐明果蝇肠道中ESG与间隔连接蛋白的关系。这些研究将有助于从长远角度理解蜗牛家族转录因子ESG调控的关键转录程序是如何维持肠道组织稳态的，并扩大我们对蜗牛家族影响组织稳态、影响器官功能和推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.