流感是重要人畜共患病，严重威胁人类和动物健康。流感病毒的致病性是由多个基因及其编码蛋白决定的，M基因及其编码蛋白发挥着重要作用，但其分子机制尚不完全清楚。我们前期研究发现蝙蝠流感病毒M基因被同源性很高的两个哺乳动物来源M基因（人PR8/H1N1和猪TX98/H3N2）替换后的重组病毒在小鼠体内展现出显著的致病性差异。前期研究结果为我们进一步阐明M基因影响流感病毒致病性的分子机制奠定了坚实的基础。本项目将继续研究禽源H9N2病毒的M基因是否影响流感病毒对哺乳动物的致病性，结合前期研究发现的差异氨基酸位点，通过序列比对、部分替换、定点突变、病毒拯救和动物试验等方法确定M基因影响流感病毒致病性的关键区域和关键氨基酸位点，研究其如何影响与病毒蛋白间的相互作用、病毒样颗粒形成及形态、病毒核酸复制转录和包装效率，进而来阐明M基因影响流感病毒对哺乳动物致病性的分子机制，为流感病毒防控提供新的科学依据。

Influenza is an important zoonotic disease for humans and animals. The viral pathogenesis of influenza virus is associated with multiple genes and their encoded proteins. The M gene influence on pathogenesis is crucial, but the mechanisms of how M gene affects pathogenesis are still not completely understood. Our previous studies demonstrate that the chimeric bat influenza virus containing M gene from either the human origin PR8/H1N1 virus or swine origin TX98/H3N2 virus, which is highly identical to each other, showed significantly difference in pathogenicity in mice; which provides a solid foundation for us to elucidate the mechanisms of M gene influencing viral pathogenicity. In this proposal, we will investigate whether the M gene of the H9N2 virus, which has contributed internal genes to important zoonotic influenza viruses such as H5N1 and H7N9 viruses, also enhances virulence in mice in the genetic backbone of the chimeric bat influenza virus. Meanwhile, we will identify the key regions and amino acids in the M gene-encoded proteins critical for viral pathogenesis by using sequence comparison, partial replacement, multiple and single mutation, virus rescue and animal pathogenicity studies. Molecular mechanisms of M gene influencing viral pathogenesis will be elucidated through studying interaction of M1/M2 proteins with viral proteins（HA and NA）, the formation efficiency of virus like particles (VLPs) using different M1/M2, VLP morphology under the electron microscope, the co-localization of M1/M2 with HA and NA by the confocal microscope, how different M1/M2 influences viral replication (vRNA) and transcription (mRNA) level and viral packaging efficiency. Our results will provide novel insights on biology of influenza virus and understanding of molecular mechanisms of M gene influencing viral pathogenicity, resulting in necessary scientific knowledge for prevention and control of influenza.