Molecular and acute temperature stress response characterizations of caspase-8 gene in two mussels, Mytilus coruscus and Mytilus galloprovincialis

The caspase family represents aspartate-specific cysteine proteases that play key roles in initiation of apoptosis in various cells response to environmental stress. In this study, two caspase-8 cDNA sequences were cloned from two Mytilus mussels, Mytilus coruscus (Mccaspase-8) and Mytilus galloprovincialis (Mgcaspase-8), respectively. The full-length cDNA of Mccaspase-8 was 1884 bp, including a 5′-terminal untranslated region (UTR) of 140 bp, a 3′-terminal UTR of 238 bp and an open reading frame (ORF) of 1506 bp encoding a polypeptide of 501 amino acids. The 1775 bp full-length Mg caspase-8 cDNA sequence contained an ORF of 1488 bp encoding a polypeptide of 495 amino acid residues, a 5′-UTR of 51 bp and a 3′-UTR of 236 bp. Both the Mccaspase-8 and Mgcaspase-8 amino acid sequences contained two highly conservative death effector domains (DEDs) at N-terminal, the caspase family domains P20 and P10 and the caspase family cysteine active site ‘KPKLFFIQACQG’. Phylogenetic analysis revealed that Mccaspase-8 and Mgcaspase-8 were clustered with the caspase-8 from other organisms, with the close relationship with caspase-8 from mollusk. Quantitative real-time reverse transcription PCR (qRT-PCR) analysis indicated that the predominant transcripts of Mccaspase-8 were in mantle and gonad tissue of M. coruscus and the high expression levels of Mgcaspase-8 were in digestive gland and gill tissue of M. galloprovincialis, respectively. The impacts of temperature stress on Mccaspase-8 and Mgcaspase-8 expressions were tested in gill tissue and hemocytes of both species. Our results showed that both Mccaspase-8 and Mgcaspase-8 transcripts and caspase-8 activity in gill tissue and hemocytes could be induced significantly after cold and heat stress (p < 0.05) and that these responses different between tissues and species. These results suggested that caspase-8 might play an important role in response to temperature stress and in determining cellular thermal tolerance limits in M. coruscus and M. galloprovincialis.