The PB2 and M genes are critical for the superiority of genotype S H9N2 virus to genotype H in optimizing viral fitness of H5Nx and H7N9 avian influenza viruses in mice

Abstract

Genotype S H9N2 avian influenza virus, which has been predominant in China since 2010, contributed its entire internal gene cassette to the genesis of novel reassortant influenza viruses, including H5Nx, H7N9 and H10N8 viruses that pose great threat to poultry and humans. A key feature of the genotype S H9N2 virus is the substitution of G1‐like M and PB2 genes for the earlier F/98‐like M and PB2 of genotype H virus. However, how this gene substitution has influenced viral adaptability of emerging influenza viruses in mammals remains unclear. We report here that reassortant H5Nx and H7N9 viruses with the genotype S internal gene cassette displayed enhanced replication and virulence over those with genotype H internal gene cassette in cell cultures as well as in the mouse models. We showed that the G1‐like PB2 gene was associated with increased polymerase activity and improved nuclear accumulation compared with the F/98‐like counterpart, while the G1‐like M gene facilitated effective translocation of RNP to cytoplasm. Our findings suggest that the genotype S H9N2 internal gene cassette, which possesses G1‐like M and PB2 genes, is superior to that of genotype H, in optimizing viral fitness, and thus have implications for assessing the potential risk of these gene introductions to generate emerging influenza viruses.

G1-like M and PB2 genes are preferentially incorporated into H7N9 progeny virions during genetic reassortment

“…Furthermore, the H9N2 virus with the G1-like M gene exhibit an early surge of viral mRNA and genomic RNA production, suggesting of increased fitness of the virus [13]. Consistently, Hao et al found that H5Nx and H7N9 viruses harbouring the G1-like PB2 and M genes display better viral fitness than those with F/98like PB2 or M genes and have high virulence and replication capacity in chickens and mice [11,12].…”

“…The S genotype, which differs from F/98-like viruses (genotype H) only in their M and PB2 genes [11,12], has not been replaced by a new genotype since 2010 [2]. As S genotype viruses carry the genetic backbone of F/ 98-like viruses (genotype H) plus the M and PB2 genes of the G1-like viruses, it is presumed that the G1-like M and PB2 genes confer better viral fitness over F/98-like counterparts.…”

H9N2 virus-derived M1 protein promotes H5N6 virus release in mammalian cells: Mechanism of avian influenza virus inter-species infection in humans

“…A systematic review reported seroprevalence to H9N2 virus at 1-43% in avian-exposed human populations [49], and the seroprevalence of H9N2 antibodies in poultry workers in China was reported at 11.2% [50], suggesting significant infectivity of H9N2 AIVs in humans. Notably, H9N2 AIVs are regarded as "enablers" because they can donate their internal genes through reassortment to produce novel reassortants with higher human infectivity [7][8][9][10][11][12]. Given that the replacement with the G1-like M gene is a critical change in generating the G57 genotype of H9N2 influenza viruses [22], we focused on the contribution of the H9N2 virusderived M gene to the replication of H5N6 virus in mammalian (human) cells.…”

“…Genetic drift and genetic reassortment are two types of evolutionary changes that occur in influenza viruses [6]. The G57 genotype of H9N2 AIVs is regarded as a principal donor of viral genes through reassortment with co-circulating influenza viruses and resulted in zoonotic reassortants (H5N6, H7N9, H10N8 and H10N3 viruses) [7][8][9][10][11][12], indicating that the H9N2 virus-derived internal genes are crucial in the cross-species transmission of AIVs to humans. Among such reassortants, H7N9, H10N8 and H10N3 viruses are endemic in China; while H5N6 viruses have been reported in several countries carried by migratory birds [13][14][15].…”

The Packaging Regions of G1-Like PB2 Gene Contribute to Improving the Survival Advantage of Genotype S H9N2 Virus in China

“…The genotype S (G57) H9N2 viruses generated through the reassortment of F98like viruses by substituting their M and PB2 genes with those of the G1-like emerged first in 2007 and have become predominant in China since 2010s (Gu et al, 2014(Gu et al, , 2017. Although the roles of G1-like M and PB2 reassortment in H7N9 and H5Nx viruses have been well characterized (Hao et al, 2019(Hao et al, , 2020, the impact of G1-like PB2 on H9N2 virus fitness is yet to be investigated.…”