The Potential Role Of Aj-MMD2 And Aj-VLRA In The Innate Immune Response Process Of Apostichopus Japonicas

The sea cucumber,Apostichopus japonicas,is a very important economic species in China.With the rapid development of sea cucumber aquaculture industry,sea cucumber disease has become a serious issue.In this study,we reported the roles of two genes in innate immune response process of A.japonicas.The complete cDNA sequences of the two immune-related genes were first cloned from the sea cucumber Apostichopus japonicas including monocyte to macrophage differentiation factor 2(MMD2)and variable lymphocyte receptor a diversity region(VLRA).The full-length cDNA of Aj-MMD2 was 1243 bp,including a 777 bp open reading frame(ORF)encoding 258 amino acids with a HlyIII domain and 7 predicted transmembrane helices.The full-length cDNA of Aj-VLRA was 3072 bp,including a 1995 bp ORF encoding 664 amino acids with LRR domains,a predicted transmembrane helices and a signal peptide in the N-terminus.As determined by quantitative real-time RT-PCR,Aj-MMD2 and Aj-VLRA transcripts were ubiquitously expressed in all four tissues of Apostichopus japonicas including body wall,longitudinal muscles,intestine and respiratory tree.Expression levels of Aj-MMD2 and Aj-VLRA were all up-regulated after challenge with four common marine bacteria and increased gradually following the concentration of the bacterium.In situ hybridization demonstrated that the expression of Aj-MMD2 and Aj-VLRA were widely distributed in four tissues and especially in the cytoplasm of epidermal cells.The recombined Aj-VLRA protein with the LRR domains exhibited the binding activities to bacteria including M.lysodeikticus(G+)and V.anguillarum(G-).Collectively,the results suggest that Aj-MMD2 and Aj-VLRA were related to an innate immune response of Apostichopus japonicas.