Abstract
Molting behavior in insects is controlled by the ecdysis triggering hormone (ETH), eclosion hormone (EH) and the crustacean cardioactive peptide (CCAP). At present, the regulation of molting behavior in crustaceans remains unclear. Here, we studied the roles of ETH, EH, and CCAP in the molt regulation of the crab, Scylla paramamosain from their expression pattern and in vivo assays. The results showed that transcripts of ETH, EH, and CCAP were mainly localized in thoracic ganglia and fluctuated periodically with the molting cycle. When ETH or CCAP was knockdown at early premolt stage (D0), molting of crabs was interrupted and all animals died at late premolt stage (D2). While the EH gene was knock-down, most crabs were dead before D2. Injection of synthetic peptide for ETH or CCAP rescued ETH- or CCAP-gene knock-down crabs separately. However, none of peptides could rescue dsEH-injected crabs. At D0 stage, knockdown of ETH down-regulated the transcriptions of EH and CCAP; while ETH was up-regulated when EH was knockdown. At D2 stage, ETH transcripts levels were reduced with the injection of dsEH but increased with the same dose of dsETH as crabs at D0 stage. Co-injection of dsETH and dsEH down-regulated ETH at D2 stage. Results showed that ETH, EH, and CCAP play essential but different roles in molt regulation in mud crab. In summary, the result of this study contributes to the discovery of different molecular mechanisms between Insecta and Crustacea and may provide insight to develop fishery drugs that helps aquacultured crustaceans to molt successfully.
Highlights
Insects and crustaceans share a number of similar hormones in the regulation of molting and reproduction
Results show that ecdysis triggering hormone (ETH), eclosion hormone (EH), and crustacean cardioactive peptide (CCAP) are essential for the regulation of molting behavior in mud crabs
Compared to ETH and CCAP, EH appears to have a specific function on the formation of new epidermis at premolt stage as synthetic peptides for ETH and CCAP can’t offset the gene knock-down effect of EH (Figures 3D–I)
Summary
Insects and crustaceans share a number of similar hormones in the regulation of molting and reproduction. During the molting of insects, many neuropeptides related to molting were regulated by precise change of ecdysteroid titer to prepare for the event (Zitnan and Adams, 2012). These neuropeptides include the ecdysis triggering hormone (ETH), eclosion hormone (EH) and Essential Neuropeptides Regulating Crab Ecdysis crustacean cardioactive peptide (CCAP), etc. These hormones are released in large quantities, which in turn initiates the onset of molting behavior (Zieger et al, 2021) Whether these neuropeptides have similar functions and regulation modes in crustaceans is still unknown. Neuropeptides that induce molting behavior include ecdysis-triggering hormone (ETH) (Shi et al, 2019a; Minh Nhut et al, 2020; Shen et al, 2021), eclosion hormone (EH) (Hull et al, 2009; Zhou et al, 2017; Scott et al, 2020), crustacean cardioactive peptide (CCAP) (Veelaert et al, 1997; Arakane et al, 2008; Jackson et al, 2009), etc
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