Associations of chicken Mx1 polymorphism with antiviral responses in avian influenza virus infected embryos and broilers

Abstract

Avian influenza virus (AIV) is a major respiratory disease of poultry that causes catastrophic losses to the poultry industry. The Mx protein has been shown to confer antiviral responses to influenza viruses in mice. One nonsynonymous substitution (S631N) in the chicken Mx protein is reported to be associated with resistance to AIV infection in vitro. The previous studies suggested controversy over whether this substitution in the Mx protein plays an important antiviral role in AIV infection in the chicken. It would be intriguing to investigate if the substitution is associated with resistance to AIV infection both in ovo and in vivo in chickens. In this study, the embryos and young chicks were generated from the cross of Mx1 heterozygous (S631N) parents with an expected segregating ratio of 1:2:1 in the progeny. A PCR length polymorphism was developed to genotype the Mx1 gene from 119 embryos and 48 chickens. The embryonated chicken eggs were inoculated with 10(6) 50% embryo infectious dose (EID(50)) H5N9 AIV on d 13. Hemagglutinating units in allantoic fluid were determined at 48 h postinoculation. For the in vivo study, twenty-four 1-wk-old broilers were inoculated with 10(6) EID(50) H5N3, and virus titers in lungs were evaluated at d 4 postinoculation. This is the first report revealing no significant association between Mx1 genotypes and low pathogenesis AIV infection both in ovo and in vivo in the chicken. Total RNA samples were isolated from chicken lung tissues in the in vivo study, and the Mx1 mRNA expression assay among 3 genotypes also suggested that only heterozygote birds had significantly greater expression with AIV infection than noninfected birds. A recombination breakpoint within Mx1 gene was also first identified, which has laid a solid foundation for further understanding biological function of the Mx1 gene in chickens. The current study provides valuable information on the effect of the Mx1 gene on the genetic resistance to AIV in chickens, and Mx1 will not be applicable for enhancing genetic resistance to AIV infection in chickens.

Pandemic Influenza A Viruses Escape from Restriction by Human MxA through Adaptive Mutations in the Nucleoprotein

“…The recombinant H5N1 virus with the single MxA resistance mutation L283P (H5N1-NP-L283P) grew slightly less well than the parental H5N1 strain, while the double mutant virus H5N1-NP-R100I,F313Y showed comparable growth (Figure 5E). Intriguingly, the latter virus showed severely impaired replication efficiency in avian LMH cells which lack antiviral Mx proteins [37]–[39] (Figure S8). We conclude that MxA resistance is linked to impaired viral growth and may be easily lost in the absence of selective pressure.…”

Genetic Variation within the Mx Gene of Commercially Selected Chicken Lines Reveals Multiple Haplotypes, Recombination and a Protein under Selection Pressure

“…Polymorphisms of the Mx gene have been reported in multiple breeds of chickens, including Australorp, Fayoumi, Japanese native chickens, Indonesian native chickens, White Leghorns, Broilers and inbred laboratory lines [5], [7]–[10]. Most of these reports have focused primarily on exon 14 (13 th coding exon) and the S631N variant, though other non-synonymous variants have been identified in other exons, and multiple haplotypes have been recognized.…”

“…In vivo work by Ewald et al [11] using commercial meat-type (broiler) chicks suggested that those with the N631 variant were more resistant to viral challenge than those with the S631 variant. However, other laboratories using primary chicken embryo fibroblast, transfected cells, chicken embryos, or chicks found no difference in the resistance to influenza virus infection regardless of which 631 variant was expressed [10], [12]–[15]. Furthermore, Schusser et al [14] demonstrated that neither of these Mx variants (N631 or S631) had GTPase activity, which is essential for antiviral activity [16].…”

Chicken Mx gene polymorphisms in Indian native chicken breeds and White Leghorn by real time multiplex allele specific PCR

“…A non-synonymous mutation at position 2032 of chicken Mx gene responsible for variation of aminoacid (Ser to Asn) in protein has been demonstrated to be responsible for negative to positive antiviral activity of Mx protein (Ko et al, 2002(Ko et al, , 2004. Recently this SNP have been demonstrated to confer more resistance in chicken to in vivo experimental infection of highly pathogenic avian influenza virus (HPAIV) (Ewald et al, 2011, Wang et al, 2012, Fulton et al, 2014. SNP at 2032 have been analyzed in various chicken breeds (Li et al, 2006, Seyama et al, 2006, Balkisson et al, 2007.…”