Emergence of developmental and genomic complexity in a basal vertebrate

描述（由申请人提供）：基于组织学分析和经典的免疫挑战实验，40年前，在无颌的基底脊椎动物七鳃鳗中存在适应性免疫系统。许多比较免疫学家认为，七鳃鳗一定拥有免疫球蛋白，因为哺乳动物在免疫反应中使用它们。然而，免疫球蛋白的证据是模糊的。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作为抗体。这种七鳃鳗抗体，被称为可变淋巴细胞受体（VLR），利用富含亮氨酸的重复基序使其受体面向。类似于免疫球蛋白系统，尽管可能不是因为共同的祖先，VLRs也利用遗传重组机制产生巨大的体细胞抗体多样性。考虑到七鳃鳗的古老自然历史，以及比较生物学家将其作为原始脊椎动物的“外群”，这一发现是出乎意料的。这一发现引起了人们对VLR系统免疫学方面的强烈兴趣。尽管它位于基底，但七鳃鳗已被证明是一个有价值的新信息储存库，它的不同之处在于它的相似之处。在这种程度上，我们最近发现：(1)VLR除了作为抗体受体的作用外，在早期胚胎发育中起着关键作用；(2) VLR参与为构建免疫系统提供细胞微环境，随后产生表达这些抗体的细胞；(3)程序性基因组重排在胚胎发生过程中重组VLR位点。我们的提案的具体目标是围绕这三个观察，并利用两个pi的互补专业知识，实验工作的七鳃鳗的可追溯性，以及加州理工学院为其功能研究创建的大型基础设施。我们提出了一套完整的实验，以进一步定义VLR的发育作用，并阐明VLR基因座发生胚胎基因组重排的早期VLR库和逻辑。我们在这条研究路线上的首要目标是了解允许复杂基本过程合并的生物学策略，在这种情况下，涉及免疫保护和发育。这三个独立的目标由VLR系统的各个方面密不可分地联系在一起，包括必要的基础实验和更冒险的实验。

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.