Cardiac Transcriptome and Histology of the Heart of the Male Chinese Mitten Crab (Eriocheir sinensis) under High-Temperature Stress

High temperatures are important environmental stressors affecting the metabolism, growth, immunity, and mortality of Chinese mitten crabs (Eriocheir sinensis). In this study, Chinese mitten crabs were divided into two groups and exposed to temperatures of 35 °C (thermal stress group) or 25 °C (control group) for 24 h, and the transcriptome of the heart was analyzed. There were 4007 differentially expressed genes (DEGs) between the thermal stress and the control groups, including 2660 upregulated and 1347 downregulated genes. Heat shock proteins (HSPs) and transcription factors (TFs) were temperature-sensitive DEGs in Chinese mitten crabs. DEGs mainly focused on protein processing in the endoplasmic reticulum, ribosome biogenesis, glycine, serine, and threonine metabolism, protein export, and insect hormone biosynthesis pathways. A total of 28,916 SSRs and 59 TF families, including 851 TFs, were detected among all unigenes of E. sinensis transcripts. The qRT-PCR results for the HSPs and apoptotic DEGs from the heart exhibited the same trends as those in the E. sinensis transcriptome data. Results of light microscopy analyzing histological sections of the heart indicated that most myocardial fibers were lysed, and the number of nuclei and the connective tissue contents between the myocardial layers were both reduced following 35 °C exposure for 24 h.