Identification of two distinct molt-inhibiting hormone-related peptides from the giant tiger prawn Penaeus monodon

Six peptides belonging to the crustacean hyperglycemic hormone (CHH) family were isolated from extracts of the sinus glands of the giant tiger prawn Penaeus monodon by reverse-phase high-performance liquid chromatography. These were designated Pem-SGP-A to Pem-SGA-F (Pem, Penaeus monodon; SGP, sinus gland peptide) and their amino-terminal amino acid sequences were analyzed. Five of the 6 peptides (Pem-SGP-A, -B, -D, -E, and -F) exhibited similar amino acid sequences to those of CHH peptides that had been characterized previously from the same prawn species by the other research groups, while 1 peptide (Pem-SGP-C) exhibited a novel sequence. Pem-SGP-C showed sequence similarity to known putative molt-inhibiting hormones (MIHs), particularly to an MIH from the kuruma prawn Penaeus japonicus, and less similarity to the CHHs determined thus far. Two similar complementary DNAs encoding Pem-SGP-C were cloned and found to encode very similar but distinct peptides, which were named Pem-SGP-C1 and Pem-SGA-C2. The open reading frame of each cDNA consisted only of a signal peptide and an MIH-like peptide. We also cloned 2 corresponding genes, both of which consisted of 3 exons and 2 introns. Analyses by reverse transcriptase polymerase chain reaction demonstrated that both Pem-SGP-C1 and Pem-SGP-C2 transcripts were detected only in cDNA synthesized using total RNA from the eyestalk but not in that from brain, thoracic ganglia, abdominal ganglia, abdominal muscle, hepatopancreas, or heart tissue of P. monodon.