RNA依赖的RNA聚合酶对鸡传染性法氏囊病病毒致病性影响的分子机制研究

Infectious bursal disease（IBD）is a highly contagious and immunosuppressive disease for chickens between 3-6 weeks age. It is caused by the infectious bursal disease virus (IBDV), which belongs to the Avibirnavirus genus of the Birnaviridae family, and its genome contains two segments of double strands RNA. Replication of IBDV depends on RNA-dependent RNA polymerase (RdRps, or VP1) encoded by segment B. Although segment B was reported to determine replication and pathogenicity of virus, its molecular basis is unclear. This study aims to investigate the effect of conserved amino acids in VP1 protein on virus replication and pathogenicity, and further to reveal the molecular pathogenic mechanism of IBDV with VP1. vvIBDV (Gx strain) was isolated and identified in the laboratory, which was passaged in SPF chichen embryo and chicken embryo fibroblast cells to obtain attenuated IBDV (Gt strain). In this program, a series of recombinant virus, including mosaic virus and mutant virus, will be rescused based on Gx strain and Gt strain using reverse-genetics system. To study molecular basis for virus replication and pathogenicity, pivotal amino acid sites will be determined by analyzing the biological characteristics of these recombinant viruses in vivo and in vitro. Then, RNA polymerase activity will be analyzed with mutant of VP1 protein influenced by the amino acid site. It will help to well understand pathogenic mechanism and genetic evolution of IBDV by studying its molecular basis and mechanism for pathogenicity of polymerase protein (VP1).

鸡传染性法氏囊病（IBD）是由传染性法氏囊病病毒（IBDV）引起的危害雏鸡的一种急性、高度接触性传染病。IBDV基因组由两个节段的双股RNA组成，B节段编码RNA依赖性的RNA聚合酶蛋白（VP1）。研究报道B节段能够影响病毒的复制和致病性，但其确切分子基础至今不清楚。本研究拟以超强毒力IBDV（Gx株）以及经体外传代致弱IBDV（Gt株）为研究对象，利用本课题组建立的IBDV反向遗传操作系统，构建嵌合病毒及突变病毒，研究重组病毒的生物学特性，确定影响病毒复制和致病性的氨基酸位点，揭示RNA聚合酶影响病毒复制和致病性的分子基础。进而，通过分析关键性氨基酸位点对RNA聚合酶活性的影响，初步探讨RNA聚合酶影响IBDV致病性的分子机制，为了解IBDV的致病机制和遗传进化提供理论基础。

本项目研究证实：VP1蛋白是影响IBDV致病力的重要因素；VP1 N端145-147位氨基酸是影响IBDV致病性的重要分子基础，其分子机制是通过改变VP1的聚合酶活性进而影响到病毒复制；病毒蛋白（VP3）和宿主因子（eIF4AII）均参与调控VP1的聚合酶活性的发挥，eIF4AII通过与IBDV VP1之间的相互作用而抑制VP1聚合酶活性，进而限制IBDV的复制，是宿主抵抗病毒感染的天然防御因子之一。