Identification, characterization and mRNA transcript abundance profiles of the carboxylesterase (CXE5) gene in Eriocheir sinensis suggest that it may play a role in methyl farnesoate degradation

The sesquiterpenoid methyl farnesoate (MF) is a de-epoxidized form of insect juvenile hormone (JH) III in crustaceans, and its precise titer plays important roles in regulating many critical physiological processes, including reproduction and ovarian maturation. Understanding the synthetic and degradation pathways of MF is equally important for determining how to maintain MF titers at appropriate levels and thus for potential applications in crab aquaculture. Although the synthetic pathway of MF has been well established, little is known about MF degradation. Previous research proposed that specific carboxylesterases (CXEs) that degrade MF in crustaceans are conserved from those of JH III. In this study, we identified a novel Es-CXE5 gene from Eriocheir sinensis. The Es-CXE5 protein contains some conserved motifs, including catalytic triad and oxyanion hole, which are characteristics of the biologically active CXE family. The phylogenetic analysis showed that Es-CXE5 belongs to the hormone/semiochemical processing group of the CXE family. Moreover, Tissue and stage-specific expression results suggested that Es-CXE5 expression in hepatopancreas was highest and associated with the hemolymph MF titer. Furthermore, Es-CXE5 mRNA transcripts were detected in both in vitro and in vivo experiments and ESA experiment in the hepatopancreas and ovary. The results of this study showed that Es-CXE5 mRNA abundance in the hepatopancreas was notably induced by MF addition but had no effect on the ovary. Taken together, our results suggest that Es-CXE5 may degrade MF in the hepatopancreas and may thus be involved in ovarian development in E. sinensis.