A janus kinase from Scylla paramamosain activates JAK/STAT signaling pathway to restrain mud crab reovirus

JAK/STAT signaling pathways are associated with the innate immune system and play important roles in mediating immune responses to virus infection. In this study, a Janus kinase gene from Scylla paramamosain (SpJAK) was cloned and characterized. The full length of SpJAK mRNA contains a 5' untranslated region (UTR) of 304 bp, an open reading frame of 3300 bp and a 3' UTR of 302 bp. The SpJAK protein contains seven characteristic JAK homology domains (JH1 to JH7) and showed 60% identity (78% similarity), 20% identity (35% similarity), and 21% identity (37% similarity) to the Litopenaeus vannamei JAK (LvJAK) protein, the Drosophila melanogaster hopscotch protein, and the Homo sapiens JAK2 protein, respectively. The mRNA of SpJAK showed high expression in the brain and nerve but low expression in the hemocyte and muscle. Moreover, the expression of SpJAK was significantly upregulated by stimulation with mud crab reovirus (MCRV), poly(I:C), and Vibrio parahaemolyticus. SpJAK significantly activated the STAT of S. paramamosain (SpSTAT) to translocate to the nucleus of Drosophila Schneider 2 cells. SpJAK significantly enhanced the activity of the promoter of the WSSV wsv069 gene that was activated significantly by SpSTAT by acting on the STAT-binding DNA motif. These results suggest that SpJAK activates the JAK/STAT pathway. Furthermore, silencing SpJAK in vivo resulted in the high mortality rate of MCRV-infected mud crabs and increased the viral load in tissues. Hence, SpJAK could play an important role in defense against MCRV in mud crab.