Cross-Species Genome-Wide Analysis Reveals Molecular and Functional Diversity of the Unconventional Interferon-? Subtype

Shields, Lauren E.; Jennings, Jordan; Liu, Qinfang; Lee, Jinhwa; Ma, Wenjun; Blecha, Frank; Miller, Laura C.; Sang, Yongming

All typical subtypes of type I IFNs were diversified in different clades of mammalian species. In mammals, intronless type I IFNs have evolved through a subtype expansion resulting in at least nine subtypes, which include IFN-α, IFN-β, IFN-ε, IFN-κ, and IFN-ω commonly found in most mammalian species as well as IFN-δ (pigs), IFN-ζ (mice), IFN-τ (cattle), and IFN-αω (or -µ) (pigs, horses, and cattle) only detected in some species (7) (8) (9) 27) . Moreover, subtypes including IFN-α, IFN-ω, IFN-δ, IFN-ζ, and IFN-τ have further diversified into multi-gene sub-clusters (7) (8) (9) 27) . In terms of subtypes and total functional gene numbers, pigs (and cattle) have the largest expansion of type I IFNs (7-9) (Figure 1 ). For example, porcine type I IFN gene loci contain 57 predictable IFN-coding genes (and 16 pseudogenes) spanning a nearly 1 Mbp genomic region and encoding at least 39 distinct IFN peptides assigned to 17 IFN-αs, 11 IFN-δs, 7 IFN-ωs, plus one each of IFN-β, IFN-ε, IFN-κ, and IFN-αω subtypes (7-9, 13).