基于Dscam选择性适应免疫的分子机制

The Down syndrome cell adhesion molecule（Dscam）is a member of the immunoglobulin super family. Dscam plays an essential function in alternative adaptive immunity in invertebrates, which can generate a variety of isoforms during the process of pathogen infection. To date, the mechanism of alternative adaptive immunity mediated by Dscam during pathogen invasion is still unknown due to its hypervariability. Previously, we have identified the hypervariable isoforms of Dscam-Ig2、3、7 in the early stage of infection by different pathogens. To further investigate how this specific recognition is generated and what is the regulation mechanism involved in the pathways mediated by these Dscam isoforms, this project will further identify the mechanism mediated by these Dscam isoforms via protein-protein interactions, loss-of-function, inhibition and activation on immune signal pathways, cell image observation and in vivo assays. What we will focus on is to study the different Dscam isoforms in: 1) characterization and immune function of specified domains with pathogens; 2) interaction with cell membranes and its regulation; 3) elimination of the invasion pathogens and its regulation; 4) the immune priming and its protection against infection. These studies will shed new light on the mechanism of alternative adaptive immunity in invertebrates which are lack of truly adaptive immunity.

唐氏综合征细胞粘附分子（Dscam）作为免疫球蛋白超家族成员，在无脊椎动物响应病原微生物感染应答中能够针对不同病原刺激生成大量不同的变构体，参与宿主免疫识别和细胞粘附等选择性适应免疫过程。但Dscam参与该过程中的分子调控机制仍不清楚。本项目拟在前期已鉴定重要海洋病毒-对虾白斑综合征病毒等病原微生物诱导的红螯螯虾Dscam-Ig2、3、7等差异型变构体基础上，利用截短实验、蛋白互作、基因定点突变/功能阻断、免疫信号通路激活与抑制、细胞影像观察、动物实验等手段，重点从以下方面关注上述差异型Dscam变构体：1）差异功能域结构与病原互作；2）与细胞膜互作过程及其调控；3）免疫清除不同病原微生物分子调控；4）介导免疫致敏特性及其保护效应差异性。通过上述研究，以期揭示Dscam变构体介导宿主免疫识别不同病原微生物的差异性及其调控宿主细胞产生选择性适应免疫的分子机制。

唐氏综合征细胞粘附分子（Dscam）作为免疫球蛋白超家族成员，在无脊椎动物响应病原感染应答中能够针对不同病原胁迫生成大量不同的变构体，参与宿主免疫识别和细胞粘附等选择性适应免疫过程。但Dscam参与该过程的分子调控机制仍不清楚，尤其是甲壳类Dscam整体胞外域或Dscam全长分子不同变构体的功能特性尚不清楚。本项目基于前期工作基础,以红螯螯虾唐氏综合征细胞粘附分子（CqDscam）为对象, 重点研究CqDscam多样性的完整胞外域变构体如何差异性识别并调控细胞吞噬病原，取得主要结果如下：1）CqDscam-Ig2、Ig3和Ig7高变结构域的互斥外显子表达不响应病原感染胁迫，但其变构体能够差异性结合病原；2）CqDscam-Ig2、Ig3和Ig7结构域多样性使其以变构体特异性嗜同型结合的方式介导细胞粘附与聚集；3）CqDscam胞外域多样性的增加抑制其嗜同型结合，而CqDscam胞外域的嗜同型结合抑制其识别结合病原；4）CqDscam胞质尾直接结合CqDock（Nck），敲降CqDock（Nck）促进了红螯螯虾血细胞对入侵病原的吞噬。上述成果首次揭示了甲壳类Dscam以节肢动物Dscam独有的变构体特异性的嗜同型结合介导细胞粘附与聚集，并首次阐明了节肢动物Dscam的嗜同型结合和识别结合病原之间的竞争关系，从而为节肢动物Dscam参与识别结合病原及其吞噬的分子机制提供了新见解。

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