title: Regulation of Y-organ ecdysteroidogenesis by molt-inhibiting hormone in crabs: involvement of cyclic AMP-mediated protein synthesis.
abstract: The crustacean neuropeptide, molt-inhibiting hormone (MIH), directly inhibits Y-organ ecdysteroidogenesis, an effect mediated by cyclic AMP (cAMP) and antagonized by calcium-calmodulin. We investigated regulation of Y-organ protein. RNA, and DNA syntheses by MIH, cAMP, and calcium in relation to steroidogenesis in vitro. Ecdysteroid production and [3H]leucine incorporation into protein were inhibited 50-60 and 80-90%, respectively, by MIH activity in eyestalk extracts (4 eyestalk equivalents), 10(-6) M forskolin, or a combination of 10(-2) M dibutyryl cAMP and 10(-4) M 3-isobutyl-1-methylxanthine (dbcAMP-IBMX). Calcium ionophore A23187 (10(-4) M) stimulated ecdysteroidogenesis two-fold, did not affect the relatively high basal (control) rate of protein synthesis, and reduced the inhibitory effects of forskolin on steroidogenesis and protein synthesis. Incorporation of [3H]uridine into RNA was unaffected by MIH, forskolin, or A23187 but was reduced 50% by dbcAMP-IBMX. Basal rates of [3H]thymidine incorporation into DNA were low and were not affected by treatments. The effects of MIH were specific; extracts of brain or muscle did not alter Y-organ steroidogenesis or protein synthesis, while muscle extract increased precursor incorporation into RNA. Eyestalk extract did not affect [3H]leucine incorporation into protein of brain, muscle, or gill. Cycloheximide (5 micrograms/ml) depressed protein synthesis 90% and steroidogenesis 60%, enhanced the inhibition induced by MIH, and blocked the stimulation of steroidogenesis induced by A23187; effects on basal steroidogenesis were evident after 1 hr. Actinomycin D (1 microgram/ml) depressed RNA synthesis 86% but did not alter basal, MIH-inhibited, or A23187-stimulated ecdysteroidogenesis during incubations. These results indicate that MIH suppresses Y-organ steroidogenesis in part by inhibiting protein synthesis at the translational level; the effect is mediated by cAMP. The stimulation of steroidogenesis by calcium, mediated by lowering cAMP, also appears to depend in part upon protein synthesis.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D003386:Brachyura / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004440:Ecdysone / Q000096:biosynthesis*; D004441:Ecdysterone / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004702:Endocrine Glands / Q000187:drug effects / Q000378:metabolism; D005260:Female; D007447:Invertebrate Hormones / Q000494:pharmacology; D007700:Kinetics; D009924:Organ Culture Techniques; D014176:Protein Biosynthesis; D012313:RNA / Q000096:biosynthesis
chemical_list: D007447:Invertebrate Hormones; C012445:molt-inhibiting hormone; D003609:Dactinomycin; D005576:Colforsin; D004440:Ecdysone; D000001:Calcimycin; D004441:Ecdysterone; D012313:RNA; D003994:Bucladesine; D003513:Cycloheximide; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine