Positional cloning of the murine flavivirus resistance gene

Inbred mouse strains exhibit significant differences in their susceptibility to viruses in the genus Flavivirus, which includes human pathogens such as yellow fever, Dengue, and West Nile virus. A single gene, designated Flv, confers this differential susceptibility and was mapped previously to a region of mouse chromosome 5. A positional cloning strategy was used to identify 22 genes from the Flv gene interval including 10 members of the 2′-5′-oligoadenylate synthetase gene family. One 2′-5′-oligoadenylate synthetase gene, Oas1b, was identified as Flv by correlation between genotype and phenotype in nine mouse strains. Susceptible mouse strains produce a protein lacking 30% of the C-terminal sequence as compared with the resistant counterpart because of the presence of a premature stop codon. The Oas1b gene differs from all the other murine Oas genes by a unique four-amino acid deletion in the P-loop located within the conserved RNA binding domain. Expression of the resistant allele of Oas1b in susceptible embryo fibroblasts resulted in partial inhibition of the replication of a flavivirus but not of an alpha togavirus

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