Study On The Role Of Down Syndrome Cell Adhesion Molecules (Dscam) In Quasi Immune Of Shrimp

White spot syndrome has been a major threat to aquaculture since its discovery.At present,the focus of the research on white spot syndrome has been on the quasi immune of shrimp.Until the discovery of immune-like proteins in shrimps,invertebrates were not thought to have specific immune responses(acquired immunity).Molecules of immunoglobulin superfamily members play important roles in the specificity of the vertebrate immune,and the most frequently found member is down cell adhesion molecules(Dscam).Dscam is highly various and can generate specific subtype molecules stimulated by different pathogens by cutting variable structural domains,which play an important role in the class immunity of invertebrates.Also,Dscam is an important pattern recognition receptor that can trigger or enhance the humoral immune response.This study explored the role of Dscam in shrimp immunity from three aspects.(1)The shrimp were first injected with inactivated white spot syndrome virus(WSSV),and followed by WSSV challenge three days later,then T-AOC and the activities of antioxidant enzymes in plasma,hemocytes,hepatopancreas,stomach and gills were examined,respectively.The results showed that after WSSV challenge,total antioxidant capacity(T-AOC)and the activities of four antioxidant enzymes in all the tissues of the experimental shrimp kept increasing for longer time,significantly higher than those of the control which were not treated with the inactivated virus.We speculated that the Dscam molecules produced by injection of inactivated WSSV may account for the specific responses of the antioxidant systems.(2)Taoping Li cloned the specific Dscam molecule generated in shrimp by immunizing shrimp with the recombinant protein VP28,and proved that there was a reaction similar to antigen "antibody" binding between VP28 and these specific Dscam molecules by yeast double hybridization.Therefore,it was speculated that these specific Dscam subtype molecules could first block virus binding to host cells by binding to VP28,so as to reduce the invasion efficiency of WSSV.In order to verify this point of view,this project designed and synthesized another polypeptide that can could bind with VP28,which was named as antiviral peptide P28.The results showed that the antiviral peptide P28 had obvious antiviral activity,which indirectly proved the role of Dscam in breaking the binding between VP28 and host cells,thus enhancing the antiviral ability of shrimp.(3)Based on the previous study on the role of Dscam,the envelop protein of WSSV with potential hub function was aimed to use for WSSV protection.In this experiment,VP62 gene was cloned and expressed in the prokaryotic expression system,which lay foundation for further analysis on the antiviral effect in the future work.