The Molecular Basis of Allorecognition in Social Amoeba

社会阿米巴同种异体识别的分子基础

• 批准号: 8574617
• 负责人: GAD SHAULSKY
• 金额: $ 30.71万
• 依托单位: BAYLOR COLLEGE OF MEDICINE
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-30 至 2017-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8574617
• 关键词: Affect; Alleles; Amino Acid Sequence; Amoeba genus; Animal Model; Binding; Biological Models; Candidate Disease Gene; Cell Adhesion Molecules; Cell Differentiation process; Cell-Cell Adhesion; Cells; Chemicals; Chemotaxis; Chimera organism; Complex; Cues; Cyclic AMP; Cytoskeleton; Defect; Development; Dictyostelium; Dictyostelium discoideum; Embryonic Development; Event; Evolution; Food; Gene Expression; Gene Expression Profile; Gene Fusion; Genes; Genetic; Graft Rejection; Grant; Haploidy; Health; Immune System Part; Infection; Inflammation; Life; Ligands; Link; Maintenance; Major Histocompatibility Complex; Mammals; Measures; Mediating; Membrane Proteins; Modeling; Molecular; Monitor; Morphogenesis; Names; Natural Immunity; Nomenclature; Null Lymphocytes; Organism; Parasites; Performance; Phosphotransferases; Play; Population; Process; Promoter Regions; Property; Protein Kinase; Proteins; Publishing; RNA Sequences; Regulation; Reporter; Role; Signal Transduction; Soil; Staging; Suppressor Mutations; Surface; System; Tertiary Protein Structure; Testing; Tissue Differentiation; Tissues; Transduction Gene; Work; base; cell behavior; cell type; chromatin remodeling; extracellular; fusion gene; gene replacement; genetic analysis; improved; marine organism; molecular phenotype; mutant; null mutation; promoter; public health relevance; receptor; research study; segregation; social; transcriptomics; transplantation medicine

DESCRIPTION (provided by applicant): Allorecognition is the ability of organisms to distinguish self from non-self, a common theme in many organisms and a central component in the evolution of multicellularity. In mammals, allorecognition is mediated by the Major Histocompatibility Complex (MHC), which is part of the immune system. The MHC facilitates identification of parasites in infection processes, and graft rejection in transplantation medicine There is evidence for the involvement of other proteins in graft rejection but there are very few model systems available to study these proteins. There are several allorecognition systems in non-mammalian systems, notably in marine organisms, but most of them are not genetically tractable. In the previous grant period we found an allorecognition system in the social soil amoeba Dictyostelium discoideum. The system is based on two proteins, TgrB1 and TgrC1 that share many properties with mammalian MHC proteins, but not their amino acid sequences. We found these trans-membrane proteins to be highly polymorphic in natural Dictyostelium populations and necessary and sufficient for allorecognition. Dictyostelium cells live as free amoebae in the soil when food is abundant but they aggregate into multicellular organisms when starved. Aggregation involves chemotaxis to extracellular cAMP and Dictyostelium is one of the best model systems for the study of chemotaxis, which is a central process in embryogenesis and in innate immunity. When Dictyostelium cells encounter cells that carry incompatible TgrB1 and TgrC1 during aggregation, they segregate from one another and form separate multicellular organisms. We propose that TgrB1 on the surface of one cell binds TgrC1 on the surface of an adjacent cell and that binding initiates a signal transduction cascade that alters cell behavior. We intend to test this hypothesis by performing allele replacement and protein-domain swapping experiments using different polymorphic alleles of the two genes. Our recent work also showed that allorecognition has an unexpected effect on chemotaxis. Many models of chemotaxis consider the process to be cell-autonomous, but our findings suggest a cooperative effect that requires interactions between cells of the same allotype. To study this revolutionary finding further, we will test the effect of allorecognition on specific aspects of chemotaxis and identify which of the well-studied chemotaxis modules is altered by allorecognition. We also propose to use transcriptome analysis and genetic suppressors to identify signal-transduction genes that integrate allorecognition. We already found several candidate genes, including chromatin remodeling components and protein kinases that are likely candidates in the process. We will study these genes in the context of allorecognition and chemotaxis and search for additional ones as well. Lastly, we propose to test the role of allorecognition in Dictyostelium development past the aggregation stage. We found that the tgrB1 and tgrC1 are enriched in prestalk cells so we propose to use conditional expression and chimeric aggregates to test the possible role of these genes in cell-type differentiation and tissue segregation.

描述（由申请人提供）：同种异体识别是生物体区分自我与非自我的能力，这是许多生物体的共同主题，也是多细胞进化的核心组成部分。在哺乳动物中，同种异体识别由主要组织相容性复合物（MHC）介导，其是免疫系统的一部分。MHC有助于识别感染过程中的寄生虫，以及移植医学中的移植物排斥。有证据表明其他蛋白质参与移植物排斥，但很少有模型系统可用于研究这些蛋白质。在非哺乳动物系统中，特别是在海洋生物中，有几种同种识别系统，但它们中的大多数在遗传上不容易处理。在前一个赠款期间，我们发现了一个异源识别系统中的社会土壤阿米巴Dictyosteelium discoideum。该系统基于两种蛋白质，TgrB1和TgrC1，它们与哺乳动物MHC蛋白质共享许多特性，但不共享它们的氨基酸序列。我们发现这些跨膜蛋白是高度多态性的天然网骨藻种群和必要的和足够的同种异体识别。当食物充足时，网骨藻细胞以游离阿米巴的形式生活在土壤中，但当饥饿时，它们聚集成多细胞生物。聚集涉及对细胞外cAMP的趋化性，并且网骨藻是用于研究趋化性的最佳模型系统之一，趋化性是胚胎发生和先天免疫中的中心过程。当网骨藻细胞在聚集过程中遇到携带不相容的TgrB1和TgrC1的细胞时，它们彼此分离并形成单独的多细胞生物体。我们提出，一个细胞表面上的TgrB1结合相邻细胞表面上的TgrC1，并且结合启动改变细胞行为的信号转导级联。我们打算通过使用两个基因的不同多态性等位基因进行等位基因置换和蛋白质结构域交换实验来验证这一假设。我们最近的工作也表明，同种识别对趋化性有意想不到的影响。许多模型的趋化性认为这一过程是细胞自主的，但我们的研究结果表明，需要相同同种异型细胞之间的相互作用的合作效应。为了进一步研究这一革命性的发现，我们将测试异源识别对趋化性特定方面的影响，并确定哪些已被充分研究的趋化性模块被异源识别改变。我们还建议使用转录组分析和遗传抑制因子来识别整合同种异体识别的信号转导基因。我们已经发现了几个候选基因，包括染色质重塑成分和蛋白激酶，它们可能是这个过程中的候选基因。我们将在同种识别和趋化性的背景下研究这些基因，并寻找其他基因。最后，我们建议测试在Dictyosteroids发展过去的聚集阶段的allorecognition作用。我们发现，tgrB1和tgrC1是丰富的prestalk细胞，所以我们建议使用条件表达和嵌合聚集体来测试这些基因在细胞类型分化和组织分离的可能作用。