Regulation of ecdysteroid biosynthesis in crayfish Y‐organs: II. Role of cyclic nucleotide‐dependent protein kinases

Abstract

AbstractThe ecdysteroid production of the crustacean molting gland, the Y‐organ, is known to be suppressed by the so‐called molt inhibiting hormone (MIH), a neuropeptide from the X‐organ‐sinus gland complex. Cyclic nucleotides appear to be involved in intracellular effects of MIH in Y‐organs. In the crab Cancer antennarius cAMP synthesis seems to be an initial event in MIH action, while in crayfish results indicate a more important role for cGMP in intracellular effects of MIH. To gain a better understanding of the intracellular mechanisms we examined the cAMP‐ and cGMP‐dependent protein kinase (A‐ and G‐kinase) activity in Y‐organs of the crayfish Orconectes limosus at different molting stages induced by eyestalk ablation. The activity ratio of cGMP‐dependent protein kinase was lower for premolt animals (0.51) than for intermolt animals (0.81), indicating a more pronounced activation of G‐kinase in Y‐organs of intermolt animals by endogenous cGMP. Moreover, preincubation of Y‐organs from destalked animals with sinus gland extract reestablished a G‐kinase activity ratio characteristic for intact animals. On the contrary, the activity ratio of A‐kinase did not vary depending on molting stage and was not altered by sinus gland extract. These results strongly suggest that MIH action in Orconectes limosus Y‐organ is mediated by cGMP rather than by cAMP. © 1993 Wiley‐Liss, Inc.