Coelomocyte Activation and the Sea Urchin Immune System

本研究旨在探讨紫海胆的免疫系统及体腔细胞激活的分子机制。Profilin基因(SpCoel1)是从体腔细胞中克隆出来的，在细胞对损伤或注射外源性体腔液时表达上调。这个分子参数表示在体腔细胞激活期间发生的变化，并将被用来评估海胆免疫系统对实验挑战所表现出的反应的幅度。我们将确定在最大化SpCoel1转录速率和激活体腔细胞方面最有效的刺激。这项分析将显示体腔细胞的识别能力，并建议这些细胞可以检测到的配体范围。为了进一步分析对外界刺激的反应，体腔细胞的增殖，包括体腔液中新细胞出现的时间进程，以及动物体内增殖中心的位置，将被表征。体腔细胞的激活很可能涉及到防御功能所需的一些新的转录体的出现。与静止细胞相比，激活细胞中转录群体的差异将被用来克隆和鉴定激活相关基因。为了提供分子上的了解，将通过比较蛋白质-DNA结合模式来分析SpCoel1的调节区，这些结合模式调节激活和静止的体腔细胞中的表达，以及在早期发育阶段该基因也在可能是体腔细胞前体的细胞中表达。棘皮动物的免疫系统在保护海胆免受感染和修复损伤方面做出快速而有效的反应。它是一个非特异性系统，其效应细胞是体腔内发现的体腔细胞。虽然与哺乳动物的免疫系统相比，这个系统看起来很原始，但它可能在功能上与高等脊椎动物免疫系统的重要元件同源。脊椎动物中作为适应性免疫基础的初级细胞反应是由同样以非特定方式发挥功能的细胞类型介导的，因此棘皮动物的防御系统可能与基本的祖先形式没有太大变化。无脊椎动物免疫系统中的基因表达和基因表达调控是生物学中一个几乎未被探索的领域。对海胆的初步研究结果已经确定了一种在防御反应的早期阶段被激活的关键基因。进一步研究该基因是如何调控的，以及该基因产物如何在免疫细胞激活中发挥作用，将为了解非特异性免疫功能的细胞机制以及这些具有生态重要性的生物如何保护自己免受伤害或感染提供新的线索。

The purpose of this investigation is to explore the immune system of the purple sea urchin, Strongylocentrotus purpuratus, and the molecular mechanisms of coelomocyte activation. The profilin gene (SpCoel1), cloned from coelomocytes, is upregulated in cells responding to injury or to injections of foreign coelomic fluid. This molecular parameter denotes changes that occur during activation of coelomocytes and will be used to assess the magnitude of responses shown by the sea urchin immune system to experimental challenge. We will identify stimuli that are most effective in maximizing the transcription rate of SpCoel1 and in activating coelomocytes. This analysis will indicate the recognition capabilities of the coelomocytes, and suggest the range of ligands these cells can detect. To further analyze the response to external stimuli, coelomocyte proliferation, including the time course of the appearance of new cells in the coelomic fluid, and the location of the proliferative centers in the animal will be characterized. Coelomocyte activation most likely involves the appearance of a number of new transcript species that are required for defense functions. Differences in the transcript population in activated cells compared to resting cells will be used to clone and characterize activation related genes. To provide a molecular understanding, the regulatory region of SpCoel1 will be analyzed by comparing protein-DNA binding patterns that regulate expression in activated and resting coelomocytes, and in early developmental stages when this gene is also expressed in cells that may be coelomocyte precursors. %%% The echinoderm immune system responds quickly and efficiently in protecting sea urchins from infection and repairing injuries. It is a non-specific system, the effector cells of which are the coelomocytes found within the body cavities. Although this system appears primitive compared to the mammalian immune system, it may be functionally homologous to important elements of higher vertebrate immune systems. Primary cellular responses in vertebrates that underlie adaptive immunity are mediated by cell types that also function in a non-specific manner, so the echinoderm defense system may not have changed much from the basic, ancestral form. Gene expression and the regulation of gene expression in invertebrate immune systems is an almost unexplored area of biology. Initial results of research on sea urchins have identified a critical gene that is activated in early stages of a defense response. Further studies of how this gene is regulated and how the gene-product functions in immune-cell activation will shed new light on the cellular mechanisms of non-specific immune function and how these ecologically important organisms defend themselves from injury or infection.