Differences in responses of grass carp to different types of grass carp reovirus (GCRV) and the mechanism of hemorrhage revealed by transcriptome sequencing

Libo He,Yongyan Pei,Rong Huang,Zuoyan Zhu,Yaping Wang,Yongming Li,Pengfei Chu,Lanjie Liao,Aidi Zhang

doi:10.1186/s12864-017-3824-1

Abstract

BackgroundGrass carp is an important farmed fish in China that is affected by serious disease, especially hemorrhagic disease caused by grass carp reovirus (GCRV). The mechanism underlying the hemorrhagic symptoms in infected fish remains to be elucidated. Although GCRV can be divided into three distinct subtypes, differences in the pathogenesis and host immune responses to the different subtypes are still unclear. The aim of this study was to provide a comprehensive insight into the grass carp response to different GCRV subtypes and to elucidate the mechanism underlying the hemorrhagic symptoms.ResultsFollowing infection of grass carp, GCRV-I was associated with a long latent period and low mortality (42.5%), while GCRV-II was associated with a short latent period and high mortality (81.4%). The relative copy number of GCRV-I remained consistent or decreased slightly throughout the first 7 days post-infection, whereas a marked increase in GCRV-II high copy number was detected at 5 days post-infection. Transcriptome sequencing revealed 211 differentially expressed genes (DEGs) in Group I (66 up-regulated, 145 down-regulated) and 670 (386 up-regulated, 284 down-regulated) in Group II. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed significant enrichment in the terms or pathways involved in immune responses and correlating with blood or platelets. Most of the DEGs in Group I were also present in Group II, although the expression profiles differed, with most DEGs showing mild changes in Group I, while marked changes were observed in Group II, especially the interferon-related genes. Many of the genes involved in the complement pathway and coagulation cascades were significantly up-regulated at 7 days post-infection in Group II, suggesting activation of these pathways.ConclusionGCRV-I is associated with low virulence and a long latent period prior to the induction of a mild host immune response, whereas GCRV-II is associated with high virulence, a short latent period and stimulates a strong and extensive host immune response. The complement and coagulation pathways are significantly activated at 7 days post-infection, leading to the endothelial cell and blood cell damage that result in hemorrhagic symptoms.

Highlights

Grass carp is an important farmed fish in China that is affected by serious disease, especially hemorrhagic disease caused by grass carp reovirus (GCRV)
In the GCRV-I-infected group, the total mortality of 42.5% was reached at 15 days post-infection, with the first fish dying at 10 days post-infection
Fish that died after infection with GCRV-I or GCRV-II showed hemorrhagic symptoms, especially in the muscle, whereas no hemorrhagic symptoms were observed in the Control group fish (Fig. 2)

Summary

Introduction

Grass carp is an important farmed fish in China that is affected by serious disease, especially hemorrhagic disease caused by grass carp reovirus (GCRV). The mechanism underlying the hemorrhagic symptoms in infected fish remains to be elucidated. The aim of this study was to provide a comprehensive insight into the grass carp response to different GCRV subtypes and to elucidate the mechanism underlying the hemorrhagic symptoms. The grass carp (Ctenopharyngodon idellus) has been an important aquaculture species in China for over 60 years, accounting for more than 18% of total freshwater aquaculture production. Grass carp hemorrhagic disease, caused by the grass carp reovirus (GCRV), is one of the most serious of these diseases [2]. GCRV infects grass carp, and rare minnow (Gobiocypris rarus), black carp (Mylopharyngodon piceus), and topmouth gudgeon (Pseudorasbora parva), causing hemorrhagic symptoms and death. GCRV is of particular interest to fish breeding geneticists aiming to identify strategies for disease-resistant breeding [4,5,6,7,8,9]

Objectives

Methods

Results

Discussion

Conclusion