Meeting Abstract

16.3  Friday, Jan. 4  Role of cyclic nucleotides, intracellular calcium and nitric oxide in the molt-inhibiting hormone (MIH) signaling pathway in Y-organs of the green shore crab (Carcinus maenas) NIMITKUL, S.*; MYKLES, D.L.; CHANG, E.S.; 1Bodega Marine Laboratory, University of California, Davis; 2Department of Biology, Colorado State University; 1Bodega Marine Laboratory, University of California, Davis snimitkul@ucdavis.edu

Molting is controlled by the X-organs/sinus gland (XO/SG) complex in the eyestalk and the thoracic Y-organs (YO). Molt-inhibiting hormone (MIH), which is produced in the XO/SG complex, inhibits the secretion of the molting hormones (ecdysteroids) from the YO. This in turn, prevents the animal from molting. Reduction in MIH results in the transition of the YO from the basal to activated state and the animal enters premolt. We proposed a model in which the MIH signaling pathway is organized into a cAMP/Ca²⁺-dependent “triggering” phase and a NO/cGMP-dependent “summation” phase. In this study, we investigated the role of cAMP, cGMP, intracellular Ca²⁺, and NO in the MIH signaling pathway in YOs from intact intermolt adult animals. cAMP analog 8-Br-cAMP (0.5 mM) and the adenylyl cyclase agonist forskolin (10 µM) did not significantly inhibit ecdysteroid secretion, while cGMP analog 8-Br-cGMP (0.5 mM) and phosphodiesterase inhibitor IBMX (0.5 mM) significantly inhibited ecdysteroid secretion. The fluorescent calcium indicator dye, Fluo-4, was used to detect calcium movement in dissociated YO cells. The results showed no large influx or efflux of calcium in YO cells incubated with SG extract. NO scavenger (cPTIO, 1 mM), NO donor (PAPA-NONOate, 0.1 mM), and NO synthase inhibitor (L-NAME, 1 mM) did not significantly affect ecdysteroid secretion. These data suggest that cGMP plays a role in the inhibitory control of ecdysteroid secretion. In contrast, the contributions of cAMP/Ca²⁺ and NO to inhibitory control may differ between basal and activated states and needs further investigation. Supported by NSF (IOS-0745224).