Transcriptomic profiles of striped snakehead fish cells (SSN-1) infected with red-spotted grouper nervous necrosis virus (RGNNV) with an emphasis on apoptosis pathway

Nervous necrosis virus (NNV), the causative agent of viral nervous necrosis (VNN) disease, has caused mass mortality of cultured marine and freshwater fish worldwide, resulting in enormous economic losses in the aquaculture industry. However, the molecular mechanisms underlying the pathogenicity of NNV are still poorly understood. In this study, the transcriptomic profiles of striped snakehead fish (Channa striatus) cells (SSN-1) infected with red-spotted grouper NNV (RGNNV) were investigated using deep RNA sequencing technique. From 254,955,234 raw reads, a total of 253,338,544 clean reads were obtained and they were assembled into 93,372 unigenes. Differentially expressed genes (DEGs) were identified from RGNNV-infected or mock-infected SSN-1 cells, including 1184 up-regulated and 1456 down-regulated genes at 3 h (h) post of infection (poi), and 1138 up-regulated and 2073 down-regulated genes at 24 h poi, respectively. These DEGs were involved in many pathways related to viral pathogenesis, including retinoic acid-inducible gene I (RIG-I) like receptors pathway, apoptosis pathway, oxidative phosphorylation, PI3K-Akt signaling pathway, and MAPK signaling pathway. Subsequent analysis focusing on the apoptosis pathway showed that the expression of Endonuclease G (EndoG) was up-regulated upon RGNNV infection at both 3 and 24 h poi. Therefore, EndoG gene was cloned and its function was further characterized. The results showed that over-expression of EndoG could also induce cellular apoptosis in SSN-1 cells, indicating that RGNNV infection might induce apoptosis of SSN-1 cells via EndoG-associated mitochondrial pathway. These results will shed a new light on the pathogenesis of NNV.