Emergence of developmental and genomic complexity in a basal vertebrate

描述(申请人提供)：40年前，基于组织学分析和经典的免疫挑战实验，七鳃鳗存在适应性免疫系统，这是一种无颌骨的基底脊椎动物。许多比较免疫学家认为七鳗鱼必须拥有免疫球蛋白，因为哺乳动物在免疫反应中使用免疫球蛋白。然而，免疫球蛋白的证据是含糊不清的。最后，在2004年，马克斯·库珀和他的同事发现七鳃鳗缺乏免疫球蛋白，而是使用一种完全不同的受体物种作为抗体。这种七鳃鳗抗体，被称为可变淋巴细胞受体(VLR)，使用富含亮氨酸的重复基序使其受体表面。与免疫球蛋白系统类似，尽管可能不是因为共同的祖先，VLRS也利用基因重组机制来产生巨大的体细胞抗体多样性。这一发现是出乎意料的，考虑到七鳃鳗的古老自然历史，以及它被比较生物学家公认为原始脊椎动物的“外类群”。这一发现引起了人们对VLR系统免疫学方面的浓厚兴趣。尽管七鳗鱼处于基础地位，但事实证明，它既有相似之处，也有不同之处，是新信息的宝贵储存库。在这方面，我们最近发现：(1)VLR除了作为抗体受体的作用外，还在早期胚胎发育中发挥关键作用；(2)VLR参与为建立免疫系统提供细胞微环境，从而产生表达这些抗体的细胞；以及(3)程序性基因组重排在胚胎发生期间重组VLR基因座。我们建议的具体目标是围绕这三个观察结果，并利用两个PI的互补专业知识、七鳗鱼用于实验工作的易驯养性以及加州理工为其功能研究创建的大型基础设施。我们提出了一套综合的实验，进一步定义了VLR的发育作用，并阐明了早期VLR的谱系和逻辑，胚胎基因组重排发生在VLR基因座上。我们在这一系列研究中的首要目标是了解生物学策略，这些策略允许融合复杂的基本过程，在这种情况下，涉及免疫保护和发育。这三个独立的目标通过VLR系统的各个方面密不可分地联系在一起，包括必要的基本实验和更冒险的实验。 公共卫生相关性：“获得性免疫”的出现被认为是脊椎动物起源的一项重大创新，在过去几十年里，了解其遗传基础和分子机制的努力一直处于生物医学研究和疫苗学的前沿。可变淋巴细胞受体(VLR)是最近在代表脊椎动物进化早期分支的谱系中发现的一种新的模块化受体系统。它在获得性免疫中的作用已被证明与免疫球蛋白相似，最近的文献将VLRs称为“抗体”，尽管它们在结构上与免疫球蛋白非常不同。我们现在有强有力的证据表明，VLRs还参与了早期胚胎的构建，这是一个与其抗体功能完全不同的角色，而且由于几个原因，特别是关于自我/非我识别和高度多样化的受体系统固有的功能生物学限制，这似乎是自相矛盾的。在根本层面上，人们感兴趣的是了解这样一个模块化的受体系统是如何出现的，它是如何发挥作用的，以及它如何被塑造成在截然不同的生物环境中部署。VLRs还具有生物技术意义[可能还具有临床意义]，因为可以对分子进行操作，使其具有许多与传统单抗相同的特征。

DESCRIPTION (provided by applicant): The existence of an adaptive immune system in the lamprey, a jawless basal vertebrate, was posited 40 years ago based on histological analysis and classical immune challenge experiments. Many comparative immunologists believed that lampreys must possess immunoglobulins because mammals employ them in their immune response. However, evidence for immunoglobulins was evasive. Finally, in 2004, Max Cooper and colleagues discovered that the lamprey lack immunoglobulins but rather employ an altogether different receptor species as an antibody. This lamprey antibody, known as the variable lymphocyte receptor (VLR) uses leucine rich repeat motifs to make its receptor face. Analogous to the immunoglobulin system, though probably not because of common ancestry, the VLRs also utilize a genetic recombination mechanism to generate vast somatic antibody diversity. This finding was unexpected, given the ancient natural history of the lamprey and its accepted use by comparative biologists as a primitive vertebrate "outgroup." This finding has led to intense interest in the immunological aspects of the VLR system. Despite its basal position, the lamprey has proven to be a valuable repository of new information as much for its differences as for its similarities. To that extent, we have recently discovered that: (1) VLR plays a key role in early embryonic development in addition to its role as an antibody receptor; (2) VLR is involved in providing the cellular microenvironment for building the immune system that subsequently yields the cells that express these antibodies; and (3) programmed genome rearrangements restructure the VLR locus during embryogenesis. The Specific Aims of our proposal are focused around these three observations and take advantage of the complementary expertise of the two PIs, the tractability of the lamprey for experimental work, and the large infrastructure that has been created at Caltech for its functional study. We propose an integrated set of experiments that further define the developmental role of VLRs and elucidate the early VLR repertoire and logic by which the embryonic genomic rearrangements occur at the VLR locus. Our overarching goal in this line of investigation is to understand the biological strategies that allow the amalgamation of complex basic processes that, in this case, involve both immune protection and development. The three independent Aims are inextricably linked by aspects of the VLR system and comprise a mixture of necessary fundamental, as well as more venturesome, experiments. PUBLIC HEALTH RELEVANCE: The emergence of "adaptive immunity" is considered a major innovation in the origin of the vertebrates, and efforts to understand its genetic underpinnings and molecular mechanisms have been at the forefront of biomedical research and vaccinology for the last few decades. The variable lymphocyte receptor (VLR) is a novel modular receptor system that has recently been discovered in a lineage representing an early offshoot in vertebrate evolution. Its role in adaptive immunity has been shown to be analogous to that of immunoglobulins, and recent literature has referred to VLRs as "antibodies" despite that fact that they are structurally very different than immunoglobulins. We now have strong evidence that the VLRs are additionally involved in building the early embryo, a completely different role than its antibody function and one that may seem paradoxical for several reasons, particularly with regard to self/non-self recognition and the functional biological limits inherent in a highly diversified receptor system. At a fundamental level, it is of interest to know how such a modular receptor system could have emerged, how it functions, and how it can be molded for deployment in vastly different biological contexts. The VLRs are also of biotechnological [and possibly clinical] relevance since the molecules can be manipulated to encompass many of the same features as conventional monoclonal antibodies.