title: Signaling events during cyclic guanosine monophosphate-regulated pigment aggregation in freshwater shrimp chromatophores.
abstract: Crustacean color change results partly from granule aggregation induced by red pigment concentrating hormone (RPCH). In shrimp chromatophores, both the cyclic GMP (3', 5'-guanosine monophosphate) and Ca(2+) cascades mediate pigment aggregation. However, the signaling elements upstream and downstream from cGMP synthesis by GC-S (cytosolic guanylyl cyclase) remain obscure. We investigate post-RPCH binding events in perfused red ovarian chromatophores to disclose the steps modulating cGMP concentration, which regulates granule translocation. The inhibition of calcium/calmodulin complex (Ca(2+)/CaM) by N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W7) induces spontaneous aggregation but inhibits RPCH-triggered aggregation, suggesting a role in pigment aggregation and dispersion. Nitric oxide synthase inhibition by Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME) strongly diminishes RPCH-induced aggregation; protein kinase G inhibition (by rp-cGMPs-triethylamine) reduces RPCH-triggered aggregation and provokes spontaneous dispersion, disclosing NO/PKG participation in aggregation signaling. Myosin light chain phosphatase inhibition (by cantharidin) accelerates RPCH-triggered aggregation, whereas Rho-associated protein kinase inhibition (by Y-27632, H-11522) reduces RPCH-induced aggregation and accelerates dispersion. MLCP (myosin light chain kinase) and ROCK (Rho-associated protein kinase) may antagonistically regulate myosin light chain (MLC) dephosphorylation/phosphorylation during pigment dispersion/aggregation. We propose the following general hypothesis for the cGMP/Ca(2+) cascades that regulate pigment aggregation in crustacean chromatophores: RPCH binding increases Ca(2+)(int), activating the Ca(2+)/CaM complex, releasing NOS-produced nitric oxide, and causing GC-S to synthesize cGMP that activates PKG, which phosphorylates an MLC activation site. Myosin motor activity is initiated by phosphorylation of an MLC regulatory site by ROCK activity and terminated by MLCP-mediated dephosphorylation. Qualitative comparison reveals that this signaling pathway is conserved in vertebrate and invertebrate chromatophores alike.
authors.affiliation: Departamento de Biologia, FFCLRP, Universidade de São Paulo, Ribeirão Preto, 14040-901 São Paulo, Brazil. mcnamara@ffclrp.usp.br
authors.forename: Sarah Ribeiro
authors.initials: SR
authors.lastname: Milograna
authors.forename: Fernanda Tinti
authors.initials: FT
authors.lastname: Bell
authors.forename: John Campbell
authors.initials: JC
authors.lastname: McNamara
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D002856:Chromatophores / Q000378:metabolism / Q000502:physiology*; D006152:Cyclic GMP / Q000378:metabolism*; D005618:Fresh Water; D033541:Palaemonidae / Q000502:physiology*; D010860:Pigments, Biological / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D002413:Cations, Divalent; D010860:Pigments, Biological; D006152:Cyclic GMP; D002118:Calcium