Type I interferon genes from the egg‐laying mammal, Tachyglossus aculeatus (short‐beaked echidna)

The type I IFN are an important group of multifunctional cytokines that have, for whatever reason, evolved to a high level of complexity in eutherian mammals such as humans and mice. However, until recently, little was known about the type I IFN systems of the other two groups of extant mammals, the marsupials and the egg‐laying monotremes. Preliminary partial type I IFN sequences from the short‐beaked echidna were previously found to cluster only with the IFN‐β subtype in phylogenetic analyses, but a lack of sequence information made interpretation of these results tenuous. Here, we report cloning of the full‐length genes of representatives from the two previously defined groups of echidna type I IFN by genomic walking PCR. Along with analysis of conserved cysteine placement and promoter elements, phylogenetic analysis incorporating these sequences strongly suggest that the two groups of echidna type I IFN genes are in fact homologueous to IFN‐α and IFN‐β, confirming that the duplication leading to these two major classes of type I IFN occurred prior to the divergence of eutherians and monotremes some 180 million years ago. Thus, even though there are major differences in gene copy number and heterogeneity, separate IFN‐α and IFN‐β gene families are a feature of the cytokine networks of all three groups of living mammals.