The NF-κB family member dorsal plays a role in immune response against Gram-positive bacterial infection in mud crab (Scylla paramamosain).

The NF-κB family is a set of evolutionarily conserved transcription factors that play central roles in various biological events. Dorsal is an invertebrate NF-κB family member that is essential for the regulation of immune responses. In the current study, the Dorsal gene from Scylla paramamosain (SpDorsal) was identified, which showed high homology to other crustacean Dorsal proteins. Expression of SpDorsal was highest in hemocytes and could be significantly changed after immune stimulations. In expression vector-transfected S2 cells, SpDorsal was mainly localized in the cytoplasm and could be efficiently translocated into the nucleus upon immune stimulations with the Gram-positive bacteria Staphylococcus aureus and poly (I:C), but not the Gram-negative bacteria Vibrio parahaemolyticus. As a transcription factor, SpDorsal could activate the promoter of S. paramamosain Hyastatin (SpHyastatin) in vitro, while S. paramamosain Cactus (SpCactus), a homolog of IκB, could interact with SpDorsal to prevent its nuclear translocation and inhibit its transcription factor activity. Silencing of SpDorsal in vivo using RNAi strategy significantly increased the mortality of crabs infected with S. aureus but not that with V. parahaemolyticus. These indicated that the SpDorsal signaling pathway could be mainly implicated in immune responses against Gram-positive bacterial infection in S. paramamosain.