Effects of cyclic nucleotides, calcium ionophore, and phorbol ester on vitellogenin mRNA levels in incubated ovarian fragments of the kuruma prawn Marsupenaeus japonicus

In crustaceans, vitellogenin (VTG, the precursor of major yolk protein) is synthesized in the ovary and/or hepatopancreas, and its synthesis is considered to be under the negative control of the vitellogenesis-inhibiting hormone (VIH), a neuropeptide secreted from the X-organ/sinus gland complex in the eyestalks. In the present study, the effects of pharmacological agents on VTG mRNA levels in incubated ovarian fragments of the kuruma prawn Marsupenaeus japonicus were examined to determine the intracellular signalling pathways for VTG synthesis. After 24 h incubation, A23187 (calcium ionophore), dibutyl-cAMP (cAMP analogue), dibutyl-cGMP (cGMP analogue), forskolin (adenylate cyclase activator), 3-isobutyl-1-methylxanthine (IBMX, phosphodiesterase inhibitor), and phorbol 12-myristate 13-acetate (PMA, protein kinase C activator) decreased VTG mRNA levels in the ovarian fragments. This result suggests that cyclic nucleotides, Ca2+, and protein kinase C are involved in the signalling pathways for the regulation of VTG mRNA levels in the ovaries. Furthermore, the inhibitory effects of sinus gland extract and the pharmacological agents on VTG mRNA were larger in previtellogenic ovaries than in vitellogenic ovaries. This result suggests that the degree of responsiveness to VIH changes during ovarian development and that the changes in responsiveness to VIH involve maturity-related changes in cellular signalling mechanisms in the ovaries.