Crustacean hyperglycaemic hormone gene from the mud crab, Scylla paramamosain: cloning, distribution and expression profiles during the moulting cycle and ovarian development

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 SpCHH2 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.