A nonsense mutation in the gene encoding 2′-5′-oligoadenylate synthetase/L1 isoform is associated with West Nile virus susceptibility in laboratory mice

A mouse model has been established to investigate the genetic determinism of host susceptibility to West Nile (WN) virus, a member of the genus flavivirus and family Flaviviridae. Whereas WN virus causes encephalitis and death in most laboratory inbred mouse strains after peripheral inoculation, most strains derived from recently trapped wild mice are completely resistant. The phenotype of resistance/susceptibility is determined by a major locus, Wnv, mapping to chromosome 5 within the 0.4-cM-wide interval defined by markers D5Mit408 and D5Mit242. We constructed a high resolution composite/consensus map of the interval by merging the data from the mouse T31 Radiation Hybrid map and those from the homologous region of human chromosome 12q, and found the cluster of genes encoding 2'-5'-oligoadenylate synthetases (2'-5'-OAS) to be the most prominent candidate. This cluster encodes a multimember family of IFN-inducible proteins that is known to play an important role in the established endogenous antiviral pathway. Comparing the cDNA sequences of 2'-5'-OAS L1, L2, and L3 isoforms, between susceptible and resistant strains, we identified a STOP codon in exon 4 of the gene encoding the L1 isoform in susceptible strains that can lead to a truncated form with amputation of one domain, whereas all resistant mice tested so far have a normal copy of this gene. The observation that WN virus sensitivity of susceptible mice was completely correlated with the occurrence of a point mutation in 2'-5'-OAS L1 suggests that this isoform may play a critical role in WN pathogenesis.