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First published online August 31, 2007
Journal of Experimental Biology 210, 3245-3254 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.007740

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Effects of elevated ecdysteroid on tissue expression of three guanylyl cyclases in the tropical land crab Gecarcinus lateralis: possible roles of neuropeptide signaling in the molting gland

Sung Gu Lee¹, Brandon D. Bader¹, Ernest S. Chang² and Donald L. Mykles^1,*

¹ Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
² Bodega Marine Laboratory, University of California-Davis, Bodega Bay, CA 94923, USA

^* Author for correspondence (e-mail: don{at}lamar.colostate.edu)

Accepted 5 July 2007

Two eyestalk (ES) neuropeptides, molt-inhibiting hormone (MIH) and crustacean hyperglycemic hormone (CHH), increase intracellular cGMP levels in target tissues. Both MIH and CHH inhibit ecdysteroid secretion by the molting gland or Y-organ (YO), but apparently through different guanylyl cyclase (GC)-dependent pathways. MIH signaling may be mediated by nitric oxide synthase (NOS) and NO-sensitive GC. CHH binds to a membrane receptor GC. As molting affects neuropeptide signaling, the effects of ecdysteroid on the expression of the land crab Gecarcinus lateralis ß subunit of a NO-sensitive GC (Gl-GC-Iß), a membrane receptor GC (Gl-GC-II) and a NO-insensitive soluble GC (Gl-GC-III) were determined. Gl-GC-Iß isoforms differing in the absence or presence of an N-terminal 32-amino acid sequence and Gl-GC-III were expressed at higher mRNA levels in ES ganglia, gill, hepatopancreas, ovary and testis, and at lower levels in YO, heart and skeletal muscle. Three Gl-GC-II isoforms, which vary in the length of insertions (+18, +9 and +0 amino acids) within the N-terminal ligand-binding domain, differed in tissue distribution. Gl-GC-II(+18) was expressed highly in striated muscle (skeletal and cardiac muscles); Gl-GC-II(+9) was expressed in all tissues examined (ES ganglia, YO, gill, hepatopancreas, striated muscles and gonads); and Gl-GC-II(+0) was expressed in most tissues and was the dominant isoform in ES and thoracic ganglia. ES ablation, which increased hemolymph ecdysteroid, increased Gl-GC-II(+18) mRNA level in claw muscle. Using real-time RT-PCR, ES ablation increased Gl-GC-Iß, Gl-GC-III and ecdysone receptor mRNA levels in the YOs ten-, four- and twofold, respectively, whereas Gl-GC-II mRNA level was unchanged. A single injection of 20-hydroxyecdysone into intact animals transiently lowered Gl-GC-Iß in hepatopancreas, testis and skeletal muscle, and certain Gl-GC-II isoforms in some of the tissues. These data suggest that YO and other tissues can modulate responses to neuropeptides by altering GC expression.

Key words: guanylyl cyclase, molting, ecdysteroid, Crustacea, Arthropoda, Y-organ, gene expression, skeletal muscle, nervous system, digestive gland, molt-inhibiting hormone, crustacean hyperglycemic hormone, ecdysone receptor, mRNA

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