Characterization Of Pathological Changes And Immune-Related Genes' Expression In Yellow Drum(Nibea Albiflora) In Response To Pseudomonas Plecoglossicida And Poly I:C Challenges

The yellow drum(Nibea albiflora)is an important marine fish species and subjected to intensive cage culture in China.The aquaculture of this species is mainly in the coast of Zhejiang and Fujian provinces.The yellow drum is susceptible to infection by pathogens from nearby cage-cultured fish such as larimichthys crocea,thereby resulting in great economic loss.This study analyzed the pathological characteristics and immune response of yellow drum after Pseudomonas plecoglossicida infection or Poly I:C injection.The results are as follows:1.The fish exhibited obvious inflammation,such as redness on the surface of the tail and fin,and severe rectal prolapse,post P.plecoglossicida infection.Hisological observation of the liver and the spleen showed lesions such as cell disorder and vacuolation72 h post P.plecoglossicida infection.The qPCR analysis showed that genes of icCu/Zn-SOD,MnSOD,ecCu/Zn-SOD,HSP70 and HSP90 were highly expressed in liver,spleen,kidney,and gill.The mRNA expression levels of these genes in liver,spleen and gill were significantly higher than those of the control after the Poly I:C injection or P.plecoglossicida infection.The aforementioned genes were up-regulated in the liver,spleen and gill during 0 ~ 72 h after Poly I:C injection.All genes' expression was up-regulated in the liver,spleen and gill during 0 ~ 48 h after P.plecoglossicida infection.At 72 h,the aforementioned genes were significantly down-regulated in the liver,spleen and gill.Compared with the control,the activities of total superoxide dismutase(T-SOD)and the contents of HSP70,HSP90 were up-regulated in the liver after Poly I:C injection.These results were consistent with the expression trend of their mRNA.Compared with control,T-SOD activities were first up-regulated and then down-regulated in P.plecoglossicida infection group;however,HSP70 and HSP90 expression showed a fluctuating trend.The cDNA of three TLR genes were cloned and analyzed.The full length of TLR3 cDNA was 3,601 bp,which cotained an ORF of 2,739 bp,encoding 912 amino acid residues;the full length of TLR5 s was 2,225 bp,which cotained an ORF of 1,932 bp,encoding 643 amino acid residues;the full length of TLR14 was 3,645 bp,which cotained an ORF of 2,634 bp,encoding 877 amino acid residues.The TLR group motifs,such as leucine-rich repeat(LRR)domains,were detected in TLR3,TLR5 s and TLR14.The amino acid sequence homology analysis showed that TLR3,TLR5 s and TLR14 in yellow drum all showed the highest similarity to TLRs from Miichthys miiuy,which were above 90%.The tissue distribution expressionof these genes showed that TLR3,TLR5 s and TLR14 were all expressed in 12 tissues.The mRNA expression levels of TLR3,TLR5 s and TLR14 in liver,spleen and gill were significantly higher than those from the control after the Poly I:C injection or P.plecoglossicida infection.The above results indicated that all these eight genes were involved in the immune regulation of the yellow drum,which provided basic data for the molecular mechanism analysis of its immune response to pathogens.