Synthesis and assay of tyrosinated analogs of a crustacean pigment-dispersing neuropeptide hormone

Circadian rhythm of pigment migration induced by chromatrophorotropins in melanophores of the crab Chasmagnathus granulata

The circadian rhythm of black pigment migration of melanophores of the crab Chasmagnathus granulata and the variation in responsiveness of these cells to pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide (CCAP), and red pigment-concentrating hormone (RPCH) were investigated. Melanophores of C. granulata possess an endogenous circadian rhythm of pigment migration, with black pigments staying more dispersed during the day period and more aggregated during the night period. This rhythm seems to be largely dependent on an endogenous release of neurohormones from eyestalks, and to a lesser extent on a primary response to illumination. beta-PDH was the most potent PDH isoform to induce pigment dispersion in both in vivo (EC50 = 0.4 pmol/animal) and in vitro (EC50 = 0.18 microM) assays. CCAP also induced pigment dispersion in vivo and in vitro assays (EC50 = 12 microM), but it was less potent than beta-PDH. In vivo, RPCH induced a low and nondose-dependent pigment aggregation, while in vitro, it had no effect on pigment migration. The responsiveness of melanophores of C. granulata to beta-PDH was significantly higher during the day period when compared to the night period in both assays, in vitro and in vivo. These results suggest that the endogenous circadian rhythm of black pigment migration is dependent on both endogenous circadian rhythm of beta-PDH synthesis and/or release from eyestalks and on an endogenous rhythm of responsiveness of melanophores to beta-PDH.

Pigment-dispersing hormones: a novel family of neuropeptides from arthropods

This report summarizes recent work on the chemistry and structure-activity relationships of crustacean chromatophorotropic pigment-dispersing hormones (PDHs) and the identification of structurally related peptides from insects. So far, the primary structures of crustacean alpha-PDH and beta-PDH and of a pigment-dispersing factor (PDF) from the grasshopper Romalea microptera have been deduced. Additionally, 17 of the 18 residues of a PDF from the cricket Acheta domesticus were identified. In the PDH/PDF family, the chain length (18 residues), terminal residues (N-terminal Asn and C-terminal Ala-NH2), and at least 50% of the amino acid sequence appear to be conserved. The functions of these peptides in insects are unknown. Detailed studies of structure-activity relationships of crustacean PDHs have been conducted, leading to the tentative identification of the message sequence, preparation of hyperpotent oxidation-resistant analogs, and synthesis of bioactive tyrosinated analogs for radioiodination. Antisera were raised against PDHs, and immunoreactive soma and fibers have been localized in the crustacean eyestalk neurosecretory system. This progress is expected to stimulate more intensive research on the PDH family.