Identification and characterization of the myeloid differentiation factor 88 gene in yellow catfish.

Myeloid differentiation factor 88 (MyD88) is an important adapter protein of the innate immune system, but it has never before been reported in yellow catfish (Pelteobagrus fulvidraco). In this study, we cloned and characterized the yellow catfish MyD88 gene. The gene was 1230 bp in length and contained an 876-bp open reading frame which encodes a polypeptide of 291 amino acid residues. The theoretical molecular mass and isoelectric point of this polypeptide were 33.4341 kDa and 5.17, respectively. Furthermore, bioinformatic and phylogenetic analyses grouped yellow catfish MyD88 with MyD88 of other fish. We found that the deduced amino acid sequence showed that the conserved N-terminal death domain and the C-terminal typical Toll/interleukin-1 receptor domain were very similar to those of other fish. Moreover, reverse transcription PCR showed that yellow catfish MyD88 is ubiquitously expressed in all tissues examined, with highest expression levels observed in the spleen and lowest levels in the intestine. Importantly, MyD88 was shown to be significantly up-regulated in the intestines after 30-day dietary supplement of Clostridium butyricum. Collectively, these results indicate that yellow catfish MyD88 has a conserved structure and is probably an important component of innate immunity in yellow catfish. This study is the first to identify and characterize MyD88 in yellow catfish, thereby providing a reference for further research into the yellow catfish innate immune system.