The cytokine genes ofOncorhynchus masou formosanusinclude a defective interleukin-4A gene

Abstract

AbstractOncorhynchus masou formosanus(Formosa land-locked salmon) is a critically endangered salmonid fish endemic to Taiwan. To begin to understand how its drastic change in lifestyle from anadromous to exclusively river-dwelling is reflected in its immune genes, we characterized the genes encoding six cytokines (IL-2A, IL-2B, IL-4A, IL-4B1, IL-4B2, and IL-17A/F2a) important for T cell responses as no genomic data is available for this fish. Interestingly, all genes appeared homozygous indicative of a genetic bottleneck. TheIL2andIL17A/F2agenes and their products are highly similar to their characterized homologs inOncorhynchus mykiss(rainbow trout) and other salmonid fish. Two notable differences were observed inIL4family important for type 2 immune responses. First,O. m. formosanuscarries not only one but two genes encoding IL-4B1 proteins and expansions of these genes are present in other salmonid fish. Second, theOmfoIL4Agene carries a 228 bp deletion that results in a premature stop codon and hence a non-functional IL-4A cytokine. This suggests a reduced ability for T cell responses against parasitic infections in this species.