Evolutionary and functional conservation of myeloid differentiation factor 88 (MyD88) in amphibian Xenopus tropicalis.

As a universal adaptor used by most TLR members, the myeloid differentiation factor 88 (MyD88) plays essential roles in TLR-mediated inflammatory response of invertebrate and vertebrate animals, and functional features of MyD88 remain largely unknown in amphibians. In this study, a MyD88 gene named Xt-MyD88 was characterized in the Western clawed frog (Xenopus tropicalis). Xt-MyD88 and MyD88 in other species of vertebrates share similar structural characteristics, genomic structures, and flanking genes, suggesting that MyD88 is structurally conserved in different phyla of vertebrates ranging from fish to mammals. Moreover, Xt-MyD88 was widely expressed in different organs/tissues, and was induced by poly(I:C) in spleen, kidney, and liver. Importantly, overexpression of Xt-MyD88 triggered a marked activation of both NF-κB promoter and interferon-stimulated response elements (ISREs), implying that it may be play important roles in inflammatory responses of amphibians. The research represents the first characterization on the immune functions of amphibian MyD88, and reveals considerable functional conservation of MyD88 in early tetrapods.