Hepatopancreas transcriptome analysis reveals the adaptation mechanism to high temperature in the clam Cyclina sinensis

Temperature is an importantly environmental factor that regulates the growth and survival of clams. To investigate the molecular changes in response to acute high-temperature stress in clam Cyclina sinensis, we conducted a transcriptional profiling. In this study, clams were cultivated at different temperature (26℃, 30℃ and 34℃) for 24 h. Hepatopancreas tissues were then collected for RNA-sequencing. Compared with the CsHe26 group (control group), 339 differentially expressed genes (DEGs) were identified in CsHe30 group containing 176 upregulated DEGs and 163 downregulated DEGs, and 649 DEGs were identified in CsHe34 group including 329 upregulated DEGs and 320 downregulated DEGs. The Go and KEGG analysis showed that DEGs were mainly involved in oxidoreductase activity, protein processing and folding, and mitogen-activated protein kinase (MAPK) signaling pathway. The analysis result of qRT-PCR showed that the expression patterns of 15 DEGs were comparable to the RNA-sequencing data indicating the reliability. Moreover, we found that Caspase3 and p38 MAPK were upregulated suggesting increased cell apoptosis. This was further evidenced by the TUNEL staining assay, which showed that high temperature stress increased the number of apoptotic cells in hepatopancreas. Overall, this work provides a valuable data resource for understanding the molecular basis of high-temperature adaptation in clams in the context of global warming and may contribute to identifying heat-tolerant candidate genes which provide potential targets for breeding heat-resistant clam strains.