Mud crab is a group of commercially important species that are found throughout the Indo-Pacific region. In this study, the full-length cDNA of molt-inhibiting hormone (Scp-MIH) was cloned from the green mud crab, Scylla paramamosain. The conceptually translated peptide precursor consists of a 78-residue mature peptide, preceded by a 35-residue signal peptide. The mature peptide shares a high identity with the other known MIHs, and contains six conserved cysteine residues that have been proposed to be functionally critical for MIH activity. Analysis of genomic sequence revealed that Scp-MIH gene was organized in a 3 exons/2 introns manner. Quantitative real-time PCR showed that Scp-MIH transcripts were detected mainly in the eyestalk ganglion and brain. During the molting cycle, Scp-MIH mRNA increased significantly from postmolt stage to intermolt stage, then decreased sharply at premolt stage. It implies that MIH is closely related to ecdysteroid production in S. paramamosain. In the ovarian cycle, Scp-MIH transcripts in some neural tissues (eyestalk ganglion and brain) increased from stage I to stage II, and reached the peak value at stage III, then declined at later stage. It suggests that MIH might be involved in the ovarian maturation in S. paramamosain.

Recently, crustacean hyperglycaemic hormone (CHH) has gained wide attention for its diverse physiological functions. In this study, two cDNA sequences encoding CHH, Sp-CHH1 and Sp-CHH2, were cloned from the eyestalk ganglia of the mud crab, Scylla paramamosain. Each conceptually translated precursor is expected to be processed into the signal peptide, the crustacean hyperglycaemic hormone precursor-related peptide (CPRP) and the CHH mature peptide. Sp-CHH1 and Sp-CHH2 share an identical sequence for the first 40 residues from the amino-terminus of the peptides, but substantially different from each other in the C-terminus. Quantitative real-time PCR (qPCR) showed that Sp-CHH transcripts were mainly detected in the eyestalk ganglia and to a much lesser extent in the brain, thoracic ganglia, stomach, hepatopancreas, heart and muscle. RNA in situ hybridization in the eyestalk ganglia indicated that the Sp-CHH was localized in the perikarya of neuroendocrine cells belonging to the X-organ of the medulla terminalis. Moreover, Sp-CHH transcripts were stage-specific changed during the moulting cycle, as it increased significantly from postmoult stage to intermoult stage, then decreased sharply at premoult stage. Sp-CHH expression levels in the eyestalk ganglia were also examined at different ovarian stages (stage I to stage V). It was found that the expression was gradually increased from stage I to stage IV, and then it was decreased at stage V. All the findings together suggested that Sp-CHH should be pleiotropic, which might inhibit the synthesis of ecdysteroids by Y-organs and be involved in promoting vitellogenesis in the mud crab.

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