Abstract：β-Thymosin is a polypeptide with antimicrobial activity. In this study, a β-Thymosin was cloned by RACE method from sea cucumber Apostichopus japonicus, named Ajβ-Thymosin. The full length of Ajβ-Thymosin was 1877 bp, with an ORF of 126 bp encoding 41 amino acids. The molecular weight of Ajβ-Thymosin was 4.6 ku and theoretical isoelectric point was 5.25. Ajβ-Thymosin contained conserved functional sequences: EVASFDKSKLK and G-actin binding residues: LKKTET. Phylogenetic analysis revealed that Ajβ-Thymosin gathered with sea urchin Strongylocentrotus purpuratus β-Thymosin. Quantitative real-Time PCR was selected to examine the expression of Ajβ-Thymosin at different tissues and developmental stages. The result indicated that Ajβ-Thymosin had most highly expression level in coelomocytes and began up-regulated at early auricularia. After four pathogens stimulus, the expression of Ajβ-Thymosin was all inhibited at 4 h. In groups of Bacillus cereus and Shewanella baltica, the expression of Ajβ-Thymosin was up-regulated at 12 h. The expression of Ajβ-Thymosin was up-regulated at 24 h in the group of Pseudoalteromonas nigrifacien and at 48 h in the group of Vibrio splendidus, respectively. The dynamic expression patterns of Ajβ-Thymosin at different times in response to different pathogens proved that it participated in the immune reaction in sea cucumber coelomocytes with different immune response abilities. The sequence and expression analyses of Ajβ-Thymosin lay foundations for studying new type antimicrobial peptides and prevention strategy of aquaculture diseases.
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2023, Vol. 42 
