MOLT-INHIBITING HORMONE MESSENGER-RNA LEVELS AND ECDYSTEROID TITER DURING A MOLT CYCLE OF THE BLUE-CRAB, CALLINECTES-SAPIDUS

Synthesis of ecdysteroid molting hormones by crustacean Y-organs is be lieved to be regulated by a neuropeptide, molt-inhibiting hormone (MM) , produced in eyestalk neural ganglia. In the present study, steady-st ate MIH mRNA and hemolymph ecdysteroid levels were determined by North ern blot and radioimmunoassay, respectively, during the molt cycle of the blue crab, Callinectes sapidus. The level of MIR mRNA dropped stea dily during premolt (D1-D4), reaching a minimum in D3/D4, then increas ed by 10-fold in postmolt (A/B) and remained elevated during intermolt (C4). These stage-specific changes in MIH mRNA levels were accompanie d by significant fluctuations in the hemolymph ecdysteroid titer. The ecdysteroid titer increased steadily to a peak of 377.0 ng/ml in D3 of premolt, then dropped to 120.0 ng/ml in D4 (just prior to molting), a nd was low during postmolt (A/B, 4.4 ng/ml) and intermolt (C4, 3.3 ng/ ml). The results represent the first report of developmental changes i n MIH gene expression and are generally consistent with the hypothesis that MIH negatively regulates ecdysteroid synthesis in crustaceans. ( C) 1998 Academic Press.