無脊椎動物唐氏綜合症黏附分子 (Dscam) 除了參與胚胎時期的神經引導機制，也可能參與專一性先天免疫機制。典型 Dscam 為鑲膜型，係由胞外區與胞質尾組成，胞外區域與其結合對象專一性有關，胞質尾組成則與後續引發的細胞反應相關。第一個蝦類 Dscam 於 2009 年從白蝦被鑑定出，其命名為 LvDscam，為特殊缺乏胞質尾的胞泌型，在不同的 WSSV 感染狀況下，LvDscam 的胞外變異區呈現特定的表現趨勢，推測其以類似脊椎動物抗體的機制辨識 WSSV。而接後屬於鑲膜型的蝦類 Dscam 也於草蝦中發現，其具有不同其他節肢動物之多變性胞質尾。由於蝦類 Dscam 具有上述的特殊性，本研究則針對其胞質尾存在與否對於 Dscam 蛋白質表現型態的差異進行探討，希望進而推論其是否與 Dscam 分泌及回歸細胞的機制有所相關性
在本研究中，我們選擇了四種分泌型 LvDscam isoform 進行蛋白質特性分析，其中 isoform 7 為未感染 WSSV 之白蝦蝦血球細胞中，表現量較高的一種 isoform，isoform 18 、 19 、 20 則是 WSSV 潛伏性感染下，白蝦蝦血球中表現量較高的三種 isoforms。
由於蝦類尚未有細胞株，本研究利用昆蟲細胞株進行重組 LvDscam 蛋白質表現 ，從中得以分析 LvDscam 蛋白質特性。所得結果顯示分泌型 LvDscam 似乎以液泡型式表現在胞質液與細胞膜，並可分泌至胞外，且此種特性並不因為 isoform 的不同而有所差異。另外，鑲膜型 LvDscam 的胞質尾部份組成元素與草蝦 Dscam 胞質尾有著極高的相似性，顯示此多變型胞質尾普遍存在於蝦類。以穿膜型胞質尾構築在胞泌型 LvDscam 上組成鑲膜型 LvDscam，我們將分析其與胞內表現位置與胞外分泌能力來釐清胞質尾在 LvDscam 所扮演的功能。
此研究提供了第一個蝦類 Dscam 蛋白質特性資訊，希望未來可進一步瞭解 LvDscam 的分泌特性及其與病原體的專一性結合現象。

Invertebrate Down syndrome cell adhesion molecule (Dscam) seems to play key roles in neuron guidance and “innate immunity with specificity”. The extracellular region of Dscam is involved in heterophilic binding specificity and pathogen recognition while the cytoplasmic tail is involved in subsequent signal transduction. In 2009, Litopenaeus vannamei Dscam (LvDscam) with extraordinary molecular diversity was identified and shown a unique tail-less secreted form. In particular, at different WSSV-infected situations, the specific population of LvDscam isoforms was appeared. These isoforms might play antibody-like function. The membrane-bound shrimp Dscam was first identified from Penaeus monodon with the cytoplasmic tail with extra hypervariable ability. Because of this uniqueness of shrimp Dscam, we investigated the characteristics of shrimp Dscam protein using the recombinant protein expression system in alternative cell line. This observation may help us to clarify the interaction between shrimp Dscam and cell.
Four tail-less secreted shrimp Dscam isoforms were selected to analyze the protein characteristics. Isoform 7 is the highest expressed isoform in heamocyte of WSSV-free shrimp, while isoforms 18, 19, and 20 are the redundant isoforms isolated from WSSV-persistent shrimp. Because shrimp cell line has not yet been established, we set to the expression platform of recombinant shrimp Dscam (rLvDscam) in Spodoptera frugiperda (Sf9) cells using baculovirus expression system and the transfection system. The cellular localization patterns of recombinant tail-less Dscam (rLvDscam) in insect cells show that rLvDscam may localize both in vesicles in cytoplasm and cell membrane. Some vesicles containing rLvDscam may involve in the processes of endocytosis or exocytosis. Moreover, tail-less rLvDscam can be secreted. Based on these information, we propose a model of how the tail-less LvDscam return cell. For membrane-bound shrimp Dscam, using the alignment of the cytoplasmic tail elements of PmDscam and LvDscam, the high identity was observed (97.78%). We’ll further analysis the localization and secreted-ability of the membrane-bound rLvDscam.
The study provides the first information about shrimp Dscam protein. In future, we hope to find the evidence supporting the Dscam involvement in the invertebrate innate immunity with specificity.

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