The evolution and immunomodulatory role of Zc3h12 proteins in zebrafish (Danio rerio)

Zc3h12 family is an important RNA-binding protein family regulating mRNA of inflammatory cytokines in mammals. However, there are few studies on their post-transcriptional level regulation of inflammatory cytokines in fish. Here, we investigated the evolution of zebrafish Zc3h12 family and explored their immunomodulatory role. Phylogenetic and syntenic analysis indicated the number of zc3h12 family members had increased ranging from a single member in invertebrates to a single copy of four members in mammals. As the most evolutionarily diverse group of vertebrates, the number of zc3h12 family members was more complex and diverse in the teleost, each member experienced different fates and followed different rules in multiple rounds of whole-genome duplication events. Thereinto, zebrafish contained three zc3h12 genes, among which zc3h12aa and zc3h12ab were duplicated from the same gene. Zebrafish Zc3h12 family could recognize the 3'-UTR regions of inflammatory cytokines through binding to the specific RNA secondary structure and negatively regulate their expression. Deletion of either Zc3h12 domains or mutation of the key amino acid in RNAase domain attenuated their modulatory effect, suggesting both domain and RNAase activity are important to the immunomodulatory role. These results elucidated the evolution of Zc3h12 family and uncovered Zc3h12-mediated post-transcriptional regulation of cytokines in zebrafish.