Browsing by Author "Bendena, W.G."

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    Comparative immunohistochemistry and cellular distribution of farnesoic acid o-methyltransferase in the shrimp and the crayfish
    (Elsevier, 2003) Gunawardene, Y.I.N.S.; Bendena, W.G.; Tobe, S.S.; Chan, S.M.
    Farnesoic acid O-methyltransferase (FAMeT) catalyzes the conversion of farnesoic acid (FA) to methylfarnesoate (MF) by the mandibular organ (MO) of crustaceans. Here we report the cellular localization of FAMeT and radiochemical assay of endogenous FAMeT activity in shrimp (Metapenaeus ensis) and crayfish (Procambarus clarkii) tissues. As in the eyestalk (ES), FAMeT is concentrated in specific neurosecretory cells of the ventral nerve cord (VNC) whereas only weak FAMeT immunoreactivity was observed in the MO. FAMeT was also detected in the ventral nerve cord, heart (HET), eyestalk, and muscle of the juvenile shrimp. Although the VNC shows the greatest FAMeT immunoreactivity, the heart extract exhibited the highest FAMeT enzymatic activity. These results suggest that FAMeT in the VNC may be inactive or inactivated at the stages of development tested. Contrary to the previous reports in other crustaceans, MO extract in shrimp shows only low FAMeT activity. The eyestalk, epidermis, ovary and testis show appreciable FAMeT activity. The presence of FAMeT in neurosecretory cells of VNC and eyestalk of shrimp and crayfish implies a possible interaction of FAMeT with the eyestalk CHH-family of neuropeptides. The widespread activity of FAMeT suggests that it has a wide spectrum of action in many tissues that contribute to the function and regulation of MF synthesis in shrimp and crayfish.
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    Function and cellular localization of farnesoic acid o-methyltransferase (FAMeT) in the shrimp, Metapenaeus ensis
    (Wiley-Blackwell, 2002) Gunawardene, Y.I.N.S.; Tobe, S.S.; Bendena, W.G.; Chow, B.K.C; Yagi, K.J.; Chan, S.M.
    The isoprenoid methyl farnesoate (MF) has been implicated in the regulation of crustacean development and reproduction in conjunction with eyestalk molt inhibiting hormones and ecdysteroids. Farnesoic acid O-methyltransferase (FAMeT) catalyzes the methylation of farnesoic acid (FA) to produce MF in the terminal step of MF synthesis. We have previously cloned and characterized the shrimp FAMeT. In the present study, recombinant FAMeT(rFAMeT) was produced for bioassay and antiserum generation. FAMeT is widely distributed in shrimp tissues with the highest concentration observed in the ventral nerve cord. Interestingly, an additional larger protein in the eyestalk also showed immunoreactivity to anti-FAMeT serum.FAMeT was localized in the neurosecretory cells of the X-organ-sinus gland complex of the eyestalk. As shown by RT-PCR, FAMeT mRNA is constitutively expressed throughout the molt cycle in the eyestalk and the ventral nerve cord. To show that our cloned gene product had FAMeTactivity, we demonstrated that expressed rFAMeT gene product catalyzed the conversion of FA to MF in a radiochemical assay. The ubiquitous distribution of FAMeT suggests that this enzyme is involved in physiological processes in addition to gametogenesis, oocyte maturation and development and metamorphosis of the shrimp. We hypothesize that FAMeT directly or indirectly (through MF) modulates the reproduction and growth of crustaceans by interacting with the eyestalk neuropeptides as a consequence of its presence in the neurosecretory cells of the X-organ-sinus gland.