Comparative transcriptome analysis provides insights into the molecular basis of circadian cycle regulation in Eriocheir sinensis.

The eyestalks of crustaceans play an essential role in controlling a variety of physiological functions by converting light into hormonal signals. To obtain a more complete description of eyestalk biology in the commercially important Chinese mitten crab (Eriocheir sinensis), we conducted comparative transcriptome analysis of eyestalks during the day and at night using high-throughput sequencing on an Illumina HiSeq 4000 platform. We obtained 47,092 unigenes-including 4771 differentially expressed genes (DEGs)-from eyestalks during the day and at night. We found that 4269 DEGs were upregulated during the day and 502 DEGs were upregulated at night. We identified five DEGs that may contribute to molting, including molt-inhibiting hormone, cuticle, catalase, aquaporin, and ubiquitin-conjugating enzyme; hence, similar to other crustaceans, Eriocheir sinensis may molt at night. We further identified eight DEGs related to behavior regulation, including three glutamate dehydrogenase genes that were upregulated during the day. Thus, changes in the eyestalks may partially compensate for daily changes in illumination in the Chinese mitten crab's normal environment. Our present study is the first genome-wide transcriptome analysis of the eyestalks of Eriocheir sinensis during the day and at night. Our findings provide a valuable insight into the molecular basis of circadian cycle regulation in crustaceans.