Evolutionary molecular biology of the interplay between the DNA damage response and innate immunity

抵御病原体和忠实修复DNA损伤的能力是单细胞和多细胞生物体的基本和进化上的古老特性。我的NSERC研究计划的主要目的是揭示先天免疫途径和细胞对DNA损伤的反应之间在进化上保守但复杂的相互作用。随着真核生物的进化，它们的病原体也随之进化，感知外来生物分子(包括DNA和RNA)的“固有”系统开始出现。对于多细胞生物体，这采取了先天免疫的形式，即细胞内识别异体和受损的DNA的蛋白质启动了导致炎症的基因通路。这种炎症会导致干扰素的产生，这对对抗病毒感染和吸引免疫细胞帮助伤口愈合非常重要，但也会引发细胞衰老和衰老。关于这些通路如何相互连接的细节只有部分了解，但最近的研究提供了证据，表明检测DNA受损和激活天然免疫的基本机制至少已有6亿年的历史。具体地说，被称为GMP-AMP合成酶(CGAS)和干扰素基因刺激物(STING)的蛋白质主要负责检测细胞质中受损的DNA，而STING可能首先进化为对影响单细胞鞭毛的病原体做出反应。在脊椎动物中，cGAS-sting既负责分泌干扰素，也负责分泌与衰老相关的炎性细胞因子，如IL-6。控制cGAS刺痛的是被称为核酸外切酶的DNA酶，它可以降解细胞质DNA，但也可以在DNA修复中发挥作用。通过分析多个脊椎动物的基因组，包括两栖动物，如Axolotl，斑马鱼和被称为斑点叉尾的“活化石”鱼类，我们追踪了一个新的核酸外切酶家族的进化起源，我们假设这些外切核酸酶在先天免疫和DNA修复中发挥作用。我们将以斑点GAR基因组为“Rosetta stone”，以Axolotl和斑马鱼为细胞和动物模型，结合CRISPR基因编辑、斑马鱼转基因模型和先进的活细胞成像技术，研究这些核酸外切酶在先天免疫信号、DNA损伤反应和修复、衰老和伤口愈合中的细胞功能。总之，这些研究将为研究生和本科生提供一个特殊的多学科培训机会，并将促进我们的长期目标，即揭示病原体防御、伤口愈合和衰老背后的DNA修复和先天免疫途径之间的复杂相互作用。

The ability to defend against pathogens and faithfully repair DNA damage are fundamental and evolutionarily ancient properties of single-cell and multicellular organisms. The major aim of my NSERC research program is to uncover the evolutionarily conserved yet complex interplay between innate immune pathways and cellular response to DNA damage. As eukaryotic organisms evolved so did their pathogens, and "innate" systems for sensing foreign biomolecules (including DNA and RNA) began to emerge. For multicellular organisms, this took the form of innate immunity, where intracellular proteins that recognize both foreign as well as damaged "self" DNA turn on gene pathways that lead to inflammation. This inflammation can result in interferon production that is important in fighting viral infections and attracting immune cells to aid wound healing but can also trigger cellular senescence and aging. The details of how these pathways interconnect are only partly understood but recent studies have provided evidence that the basic machinery underlying the detection of damaged DNA and activation of innate immunity is at least 600 million years old. Specifically, proteins called GMP-AMP Synthase (cGAS) and STimulator of Interferon Genes (STING) are chiefly responsible for detecting damaged DNA in the cytoplasm of cells, and STING may have first evolved to respond to pathogens affecting single cell flagellates. In vertebrates, cGAS-STING is responsible for secretion of both interferons and senescence-associated and inflammatory cytokines like IL-6. Keeping cGAS-STING in check are DNA enzymes called exonucleases that can degrade cytoplasmic DNA but can also play roles in DNA repair. By analysing multiple vertebrate genomes, from species including amphibians such as the axolotl, zebrafish and the "living fossil" fish known as the spotted gar, we have traced the evolutionary origins of a novel family of exonucleases that we hypothesize have a role in innate immunity and DNA repair. Using the spotted gar genome as our "Rosetta stone", and both the axolotl and zebrafish as cell and animal models, we will characterize the cellular functions of these exonucleases in innate immune signaling, DNA damage responses and repair, senescence and wound-healing by combining CRISPR gene editing, zebrafish transgenic models and advanced live-cell imaging techniques. Together, these studies will provide an exceptional opportunity for multi-disciplinary training of graduate and undergraduate trainees, and will foster our long term goal of uncovering the complex interplay between DNA repair and innate immune pathways that underlie pathogen defense, wound-healing and aging.