NAKATSUJI, T.**; SONOBE, H.; WATSON, R.D.; Univ. of Alabama, Birmingham; Konan Univ.; Univ. of Alabama, Birmingham: Molt-Inhibiting Hormone-Mediated Regulation of Ecdysteroid Synthesis by Y-organs of the American 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-Br-cAMP or 8-Br-cGMP to incubation medium significantly suppressed ecdysteroid production by Y-organs of the crayfish (Procambarus clarkii). Incubating Y-organs with synthetic MIH produced a significant increase in glandular cGMP. The increase was detectable a 2 minutes of incubation, reached a maximum by 30 minutes, and remained elevated for the duration of the 60-minute incubation. By contrast, MIH had no effect on glandular cAMP. Subsequently, Y-organs from various stages of the molt cycle were incubated with MIH, 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. The combined results suggest that molt cycle-associated changes in PDE activity may play a critical role in the ability of MIH to stimulate cGMP accumulation and suppress ecdysteroidogenesis in Y-organs of P. clarkii. Determination of PDE activity in Y-organs during a molt cycle is in progress. Grant sponsor: National Science Foundation, IBN-0213047 (RDW).
