Molecular cloning, expression analysis, and the immune-related role of a thymosin β in the goldfish, Carassius auratus.

β-Thymosins play critical roles in the regulation of many important physiological processes, but their function in teleost fishes remains poorly understood. In this study, the full-length cDNA coding for a thymosin β (Tβ) was cloned and identified in goldfish, Carassius auratus (gfTβ). The gfTβ cDNA consisted of 653 bp with an open reading frame of 135 bp that encodes a 44 amino acid polypeptide. Sequence analysis revealed one thymosin domain and a highly conserved actin-binding motif (LKKTET). Expression of gfTβ transcript was detected ubiquitously in all tissues examined, with relatively higher levels in the brain, intestine, spleen, gill, skin, kidney, and testis. Cadmium and HO exposure induced increases in gfTβ transcript levels in the liver and spleen. Moreover, gfTβ transcription was upregulated in response to LPS challenge in the spleen while Poly I:C treatment did not affect gfTβ expression. In vivo injection of recombinant gfTβ generated from an Escherichia coli system induced expression of T lymphocyte-related genes (RAG1 and CD8α). These results suggest that gfTβ may be involved in the immune response of teleost fishes via modulation of T lymphocyte development.