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-beta 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 homologous to IFN-alpha and IFN-beta, 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-alpha and IFN-beta gene families are a feature of the cytokine networks of all three groups of living mammals.
Harrison
Gavan A
GA
University of Western Sydney, School of Science, Food and Horticulture, BCRI Building, Penrith South DC, NSW 1797, Australian.
McNicol
Kelly A
KA
Deane
Elizabeth M
EM
D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000235:genetics; D007370:Interferon Type I / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D004442:Tachyglossidae / Q000235:genetics*
D007370:Interferon Type I; D003545:Cysteine