Nakatsuji T, Sonobe H, Watson RD. Molt-inhibiting hormone-mediated regulation of ecdysteroid synthesis in Y-organs of the crayfish (Procambarus clarkii): involvement of cyclic GMP and cyclic nucleotide phosphodiesterase.
Mol Cell Endocrinol 2006;
253:76-82. [PMID:
16765511 DOI:
10.1016/j.mce.2006.05.001]
[Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2006] [Revised: 03/29/2006] [Accepted: 05/02/2006] [Indexed: 10/24/2022]
Abstract
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.
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