Molecular characterization of methoprene-tolerant gene (Met) in the swimming crab Portunus trituberculatus: Its putative role in methyl farnesoate-mediated vitellogenin transcriptional activation

Methoprene-tolerant (Met) belongs to the basic helix-loop-helix (bHLH)-Per-Arnt-Sim (PAS) family of nuclear transcriptional regulators, and is the leading candidate receptor for the insect Juvenile hormone OH) and the crustacean methyl farnesoate (MF). In the present study, a full-length cDNA of Met was cloned from the swimming crab, Portunus tritubercututus (PtMet). The PtMet amino acid sequence was found to contain domains characteristic of the bHLH-PAS family proteins and to have several conserved amino acid residues specifically responsible for JH or MF binding. In addition to its extensive tissue expression, PtMet mRNA is highly expressed in the female hepatopancreas, the primary site of vitellogenin (Vg) synthesis in P. trituberculatus. PtMet expression was significantly increased in the early-vitellogenic stage of ovarian development, which indicated that likely involvement in vitellogenesis regulation. In vitro, MF induced up-regulation of PtMet and PtVg expression in the hepatopancreas, but not in the ovary. In vivo, MF induced PtMet and PtVg expression in the hepatopancreas,and only PtMet expression was induced in the ovary. Taken together, these results suggest that Met can potentially serve as a MF receptor in crustaceans. In addition, the binding of Met to MF might transcriptionally regulate Vg synthesis in the hepatopancreas. (C) 2016 Elsevier B.V. All rights reserved.