shRNA-triggered RNAi inhibits expression of NDV NP gene in chicken embryo fibroblast

RNA interference (RNAi) technology is a powerful tool for identifying gene functions. Chicken embryo fibroblast (CEF) is an ideal model for studying the interaction between avian viruses and their hosts. To establish a methodological platform for RNAi studies in CEF, three plasmid vectors expressing short hairpin RNAs (shRNAs) targeted against the Newcastle disease virus (NDV) NP gene were constructed. One of them, ndv1, was proven effective on blocking viral replication in CEF and chicken embryos. Four hours prior to infection with NDV, the CEF was transfected with the plasmids by Silent-fect. An unrelated shRNA sequence (HK) was used in mock transfection. The expression of a potent shRNA resulted in up to 2.3, 21.1 and 9.8 fold decreases in NP gene expression at 3, 6 and 9 h post infection in CEF, respectively. The ndv1 was able to completely inhibit the replication of the virus in CEF within 48 post infection. Furthermore, the pathological changes in CEF caused by NDV were delayed, and the degree of pathological changes was lighter compared with the mock transfection in the presence of ndv1. When the complex of shRNA-Silent-fect and NDV was co-injected into the allantoic cavity of 10-day-old embryonated eggs with 10(5) or 10(6) ELD(50) NDV, NDV replication was decreased by 94.14% and 62.15% after 17 h, respectively. These findings suggest that the newly synthesized NP protein is critical for NDV transcription and replication and provide a basis for identifying the functions of viral genes and screening for effective siRNAs against viruses in CEF and chicken embryo by RNAi.