The heat shock cognate protein 70 (HSC70) gene in the echiuran worm Urechis unicinctus: Cloning, tissue expression and response to sulfide exposure

To investigate the molecular characteristics of the heat shock cognate protein 70 (HSC70) gene in the echiuran worm Urechis unicinctus, the full-length complementary DNA (cDNA) sequence of HSC70 in U. unicinctus was cloned and characterized. Additionally, the expression of HSC70 in different tissues of U. unicinctus was detected after exposure to 0.25, 0.75, and 1.25 mg L^-1 Na₂S for 3, 6, 12, 24, 48, and 72 h, respectively. Results showed that the full-length cDNA of the HSC70 gene was 2305 bp and encoded a deduced 658-amino acid (aa) protein. Three characteristic structural features of the HSP70 gene family: IVLVGGSTRIPKIQK (residues 334-348), IFDLGGGTFDVSV (residues 197-210), and IDLGTTYSCV (residues 9-18), were identified in the HSC70 amino acid sequence. Multiple sequence alignment showed that HSC70 was 87.25 % identical to Meretrix meretrix at the amino acid level, and phylogenetic analyses suggested that the HSC70 gene of U. unicinctus was most closely grouped with Urechis caupo. Additionally, HSC70 was expressed in all tested tissues, with the highest expression in hemolymph. HSC70 mRNA expression was significantly increased after sulfide exposure, reaching a peak 3-6 h into the exposure, suggesting that HSC70 expression was sensitive to environmental factors. Na₂S exposure for 12 h significantly increased the muscle content of HSC70, while a significant decrease was observed after Na₂S exposure for 72 h. Taken together, our study findings suggest that the HSC70 gene is rapidly induced in U. unicinctus in response to sulfide exposure.