Improvement and applications of adeno-associated virus 2 (AAV-2) system for efficient gene transfer and expression in penaeid shrimp cells

Adeno-associated virus 2 (AAV-2)-mediated expression system is a well-developed and widely used gene transfer and expression tool in mammalian cells, but no attempt has been done to examine its infection and expression efficiency in shrimp cells. In this study, using eGFP as a reporter gene, we found that unmodified AAV-2 could infect primarily cultured shrimp hemolymph cells, but with an extremely low infection efficiency of up to 0.0067%. However, all the improvements of AAV-2 expression system tried in this study including the insertion of shrimp virus (IHHNV)-sourced P2 promoter into the AAV-2 vector (i.e. pAAV-CMV-P2-eGFP) and the inclusion of shrimp virus (IHHNV)-sourced nucleocapsid protein (IHCP) into or association of shrimp virus (WSSV)sourced tegument protein (VP26) with the capsid of the improved AAV-2 s, respectively, could significantly increase the infection and expression efficiencies of this expression system in the primarily cultured shrimp hemolymph cells in comparison with wild-type AAV-2. Moreover, from the viewpoint of improving the infection and expression efficiency, the insertion of P2 promoter did best, followed by the association of WSSV tegument protein of VP26, and the last was the inclusion of IHHNV nucleocapsid protein of IHCP. In conclusion, an improved AAV-2 expression system which consists of four expression plasmids of pAAV-CMV-P2-eGFP, pAAVRC, pHelper and pcDNA3.1-VP26 and one packaging cell line of HEK293T has been successfully developed in this study. This improved AAV-2 expression system will provide us a useful tool for efficient gene transfer and expression in shrimp cells.