title: Pigment Translocation in Caridean Shrimp Chromatophores: Receptor Type, Signal Transduction, Second Messengers, and Cross Talk Among Multiple Signaling Cascades.
abstract: Pigment aggregation in shrimp chromatophores is triggered by red pigment concentrating hormone (RPCH), a neurosecretory peptide whose plasma membrane receptor may be a G-protein coupled receptor (GPCR). While RPCH binding activates the Ca2+/cGMP signaling cascades, a role for cyclic AMP (cAMP) in pigment aggregation is obscure, as are the steps governing Ca2+release from the smooth endoplasmic reticulum (SER). A role for the antagonistic neuropeptide, pigment dispersing homone (α-PDH) is also unclear. In red, ovarian chromatophores from the freshwater shrimp Macrobrachium olfersi, we show that a G-protein antagonist (AntPG) strongly inhibits RPCH-triggered pigment aggregation, suggesting that RPCH binds to a GPCR, activating an inhibitory G-protein. Decreasing cAMP levels may cue pigment aggregation, since cytosolic cAMP titers, when augmented by cholera toxin, forskolin or vinpocentine, completely or partially impair pigment aggregation. Triggering opposing Ca2+/cGMP and cAMP cascades by simultaneous perfusion with lipid-soluble cyclic nucleotide analogs induces a "tug-of-war" response, pigments aggregating in some chromatosomes with unpredictable, oscillatory movements in others. Inhibition of cAMP-dependent protein kinase accelerates aggregation and reduces dispersion velocities, suggesting a role in phosphorylation events, possibly regulating SER Ca2+release and pigment aggregation. The second messengers IP3and cADPR do not stimulate SER Ca2+release. α-PDH does not sustain pigment dispersion, suggesting that pigment translocation in caridean chromatophores may be regulated solely by RPCH, since PDH is not required. We propose a working hypothesis to further unravel key steps in the mechanisms of pigment translocation within crustacean chromatophores that have remained obscure for nearly a century.
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Sarah Ribeiro
authors.initials: SR
authors.lastname: Milograna
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Márcia Regina
authors.initials: MR
authors.lastname: Ribeiro
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Fernanda Tinti
authors.initials: FT
authors.lastname: Bell
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil.|Centro de Biologia Marinha, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: John Campbell
authors.initials: JC
authors.lastname: McNamara
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002856:Chromatophores / Q000502:physiology*; D018871:Endoplasmic Reticulum, Smooth / Q000502:physiology; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D033541:Palaemonidae / Q000502:physiology*; D010860:Pigments, Biological / Q000378:metabolism*; D015290:Second Messenger Systems / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D010860:Pigments, Biological; D002118:Calcium