Molt-inhibiting hormone-mediated regulation of ecdysteroid synthesis in Y-organs of the crayfish (Procambarus clarkii): involvement of cyclic GMP and cyclic nucleotide phosphodiesterase.
Crustacean molt-inhibiting hormone (MIH), a polypeptide secreted by the X-organ/sinus gland complex of the eyestalks, regulates molting by inhibiting the synthesis of ecdysteroids by Y-organs. Previous results indicate the biosynthetic activity of Y-organs is likely controlled not only by the level of hemolymphatic MIH, but also by the responsiveness of Y-organs to MIH. The present studies were conducted to (a) identify the second messenger that mediates MIH-induced suppression of ecdysteroidogenesis, and (b) assess the possible involvement of cyclic nucleotide phosphodiesterase (PDE) in determining the responsiveness of Y-organs to MIH. Adding 8-bromo cAMP or 8-bromo cGMP to incubation medium significantly suppressed ecdysteroid production by Y-organs of the crayfish (Procambarus clarkii). Incubating Y-organs with MIH produced a significant increase in glandular cGMP, but MIH had no effect on glandular cAMP. The composite data indicate that MIH-induced suppression of ecdysteroidogenesis in Y-organs of P. clarkii is mediated by cGMP. Subsequently, Y-organs from various stages of the molt cycle were incubated with MIH, 3-isobutyl-1-methylxanthine (IBMX, an inhibitor of PDE), or both. Y-Organs from middle and late premolt stages were poorly responsive to MIH alone. Including IBMX in the incubation medium enhanced the responsiveness of the Y-organs to MIH at these stages. Moreover, glandular PDE activity in the Y-organs at these stages was significantly higher than other stages. The combined results suggest that molt cycle-associated changes in PDE activity affect the ability of MIH to stimulate cGMP accumulation and suppress ecdysteroidogenesis in Y-organs of P. clarkii.
Nakatsuji
Teruaki
T
Department of Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Sonobe
Haruyuki
H
Watson
R Douglas
RD
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D026461:Ecdysteroids / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D004702:Endocrine Glands / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D018978:Molting / Q000187:drug effects; D009479:Neuropeptides / Q000494:pharmacology / Q000502:physiology*
D026461:Ecdysteroids; D009479:Neuropeptides; C101529:molt-inhibiting hormone, crayfish; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D006152:Cyclic GMP