ALLEN, M.A *; CHANG, E.S; MYKLES, D.L.; Colorado State University; Bodega marine Laboratory: Regulation of Ecdysteroid Secretion in Land Crab Y-Organs

n decapod crustaceans, molting is regulated by ecdysteroids synthesized and secreted by the Y-organs, which are negatively controlled by molt inhibiting hormone (MIH) produced by the X-organ in eyestalks. MIH is a neuropeptide that suppresses production of ecdysteroids by stimulating production of cAMP and cGMP by adenylate cyclase (AC) and guanylate cyclase (GC), respectively. These cyclic nucleotides initiate a cascade that down-regulates cholesterol receptors and inactivates enzymes involved in ecdysteroid synthesis. Regulatory roles of cAMP and cGMP in this pathway are yet unclear. Some studies show that cGMP levels in Y-organs are more responsive to changes in MIH levels during the molting cycle. Other studies show that cAMP inhibits ecdysteroid production while cGMP does not. The purpose of this study is to clarify the function and importance of the two cyclic nucleotides in Y-organs of the land crab, Gecarcinus lateralis . Cell-permeable derivatives of cAMP and cGMP were used to determine the effects of cyclic nucelotides on ecdysteroid secretion of Y-organs cultured in vitro. Ecdysteroid concentration in culture media was quantified by radioimmunoassy. Preliminary results indicate cGMP inhibited ecdysteroid secretion more than cAMP. Because of the possible regulatory function of cGMP in this pathway, the expression of GC was examined. A cDNA encoding a partial sequence of GC was obtained by RT-PCR. RT-PCR using sequence-specific primers showed that GC was expressed in skeletal muscle, limb buds, intestine, and Y-organ. Supported by NSF (IBN-9904528).