Pigment Translocation in Caridean Shrimp Chromatophores: Receptor Type, Signal Transduction, Second Messengers, and Cross Talk Among Multiple Signaling Cascades.

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 IP3 and 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.

Pigment granule translocation in red ovarian chromatophores from the palaemonid shrimp Macrobrachium olfersi (Weigmann, 1836): functional roles for the cytoskeleton and its molecular motors.

The binding of red pigment concentrating hormone (RPCH) to membrane receptors in crustacean chromatophores triggers Ca²âº/cGMP signaling cascades that activate cytoskeletal motors, driving pigment granule translocation. We investigate the distributions of microfilaments and microtubules and their associated molecular motors, myosin and dynein, by confocal and transmission electron microscopy, evaluating a functional role for the cytoskeleton in pigment translocation using inhibitors of polymer turnover and motor activity in vitro. Microtubules occupy the chromatophore cell extensions whether the pigment granules are aggregated or dispersed. The inhibition of microtubule turnover by taxol induces pigment aggregation and inhibits re-dispersion. Phalloidin-FITC actin labeling, together with tannic acid fixation and ultrastructural analysis, reveals that microfilaments form networks associated with the pigment granules. Actin polymerization induced by jasplaquinolide strongly inhibits RPCH-induced aggregation, causes spontaneous pigment dispersion, and inhibits pigment re-dispersion. Inhibition of actin polymerization by latrunculin-A completely impedes pigment aggregation and re-dispersion. Confocal immunocytochemistry shows that non-muscle myosin II (NMMII) co-localizes mainly with pigment granules while blebbistatin inhibition of NMMII strongly reduces the RPCH response, also inducing spontaneous pigment dispersion. Myosin II and dynein also co-localize with the pigment granules. Inhibition of dynein ATPase by erythro-9-(2-hydroxy-3-nonyl) adenine induces aggregation, inhibits RPCH-triggered aggregation, and inhibits re-dispersion. Granule aggregation and dispersion depend mainly on microfilament integrity although microtubules may be involved. Both cytoskeletal polymers are functional only when subunit turnover is active. Myosin and dynein may be the molecular motors that drive pigment aggregation. These mechanisms of granule translocation in crustacean chromatophores share various features with those of vertebrate pigment cells.

Cyclic guanosine monophosphate signaling cascade mediates pigment aggregation in freshwater shrimp chromatophores.

The cell signaling cascades that mediate pigment movements in crustacean chromatophores are not yet well established, although Ca(2+) and cyclic nucleotide second messengers are involved. Here, we examine the participation of cyclic guanosine monophosphate (cGMP) in pigment aggregation triggered by red pigment concentrating hormone (RPCH) in the red ovarian chromatophores of freshwater shrimp. In Ca(2+)-containing (5.5 mmol l(-1)) saline, 10 micromol l(-1) dibutyryl cGMP alone produced complete pigment aggregation with the same time course ( approximately 20 min) and peak velocity ( approximately 17 microm/min) as 10(-8) mol l(-1) RPCH; however, in Ca(2+)-free saline (9 x 10(-11) mol l(-1) Ca(2+)), db-cGMP was without effect. The soluble guanylyl cyclase (GC-S) activators sodium nitroprusside (SNP, 0.5 micromol l(-1)) and 3-morpholinosydnonimine (SIN-1, 100 micromol l(-1)) induced moderate aggregation by themselves ( approximately 35%-40%) but did not affect RPCH-triggered aggregation. The GC-S inhibitors zinc protoporphyrin IX (ZnPP-XI, 30 micromol l(-1)) and 6-anilino-5,8-quinolinedione (LY83583, 10 micromol l(-1)) partially inhibited RPCH-triggered aggregation by approximately 35%. Escherichia coli heat-stable enterotoxin (STa, 1 micromol l(-1)), a membrane-receptor guanylyl cyclase stimulator, did not induce or affect RPCH-triggered aggregation. We propose that the binding of RPCH to an unknown membrane-receptor type activates a Ca(2+)-dependent signaling cascade coupled via cytosolic guanylyl cyclase and cGMP to protein kinase G-phosphorylated proteins that regulate aggregation-associated, cytoskeletal molecular motor activity. This is a further example of a cGMP signaling cascade mediating the effect of a crustacean X-organ neurosecretory peptide.

Melancolia como herança no filme Cidadão Kane / Melancholy as inheritance in the movie Citzen Kane

O texto propõe um estudo, com base na teoria Psicanalítica, sobre o filme Cidadão Kane, de Orson Welles, abordando alguns aspectos em relação à melancolia. Trata-se de considerar algumas partes do contexto fílmico (roteiro, música, montagem), assim como a biografia do autor e contexto social, como dispositivos que dão um certo relevo à idéia da impossibilidade de se fazer um luto pela perda de um objeto amado. Para além da sintomatologia clássica referida à melancolia, a ênfase é dada no processo da perda descrito por Freud em seu texto Luto e Melancolia de (1917 [1915]). O filme nos faz refletir sobre o quanto o que se herda pode estar paradoxalmente referido a uma perda. O personagem Kane, na sua infância, herda uma fortuna ao mesmo tempo em que perde o convívio com os pais; assim, o que ele não leva de sua casa (o trenó Rosebud) é o que o acompanha pelo resto da vida, enquanto significante, vinculado ao abandono. A montagem, um dos aspectos da análise fílmica, é mais detalhadamente analisada por ser considerada pelo próprio Welles como o elemento principal da obra de arte cinematográfica. Outra proposição que se apresenta, neste artigo, é a idéia de que também a montagem, neste filme, pode ser pensada como produtora de um efeito melancólico.(AU)

The text proposes a study, based on Psychoanalytical theory, about the film Citizen Kane, by Orson Welles, touching upon some aspects related to melancholy. It is about regarding some parts of the movie context (script, soundtrack, editing), as well as the authorÆs biography and the social context as social devices that award importance to the idea of the impossibility of mourning over a beloved object. Beyond the classic symptoms attributed to melancholy, the emphasis here lies on the process of loss described by Freud in ôMourning and Melancholyõ (1917 [1915]). The film makes us reflect on how much what is inherited can be paradoxically referred to a certain loss. Kane the character, in his childhood, inherits a fortune at the same time that he loses the possibility of living with his parents; thus, what he doesnÆt take from home (the sledge Rosebud) is what accompanies him for the rest of his life, as a significant, linked to the abandonment. The editing, one of the aspects of the movie analysis, is analyzed in more detail because it was considered, by Welles himself, as the main element of a movie masterpiece. Another proposition presented in this article is the idea that the editing, in this film, can also be thought as producing a melancholic effect.(AU)

Melancolia como herança no filme Cidadão Kane / Melancholy as inheritance in the movie Citzen Kane

O texto propõe um estudo, com base na teoria Psicanalítica, sobre o filme Cidadão Kane, de Orson Welles, abordando alguns aspectos em relação à melancolia. Trata-se de considerar algumas partes do contexto fílmico (roteiro, música, montagem), assim como a biografia do autor e contexto social, como dispositivos que dão um certo relevo à idéia da impossibilidade de se fazer um luto pela perda de um objeto amado. Para além da sintomatologia clássica referida à melancolia, a ênfase é dada no processo da perda descrito por Freud em seu texto Luto e Melancolia de (1917 [1915]). O filme nos faz refletir sobre o quanto o que se herda pode estar paradoxalmente referido a uma perda. O personagem Kane, na sua infância, herda uma fortuna ao mesmo tempo em que perde o convívio com os pais; assim, o que ele não leva de sua casa (o trenó Rosebud) é o que o acompanha pelo resto da vida, enquanto significante, vinculado ao abandono. A montagem, um dos aspectos da análise fílmica, é mais detalhadamente analisada por ser considerada pelo próprio Welles como o elemento principal da obra de arte cinematográfica. Outra proposição que se apresenta, neste artigo, é a idéia de que também a montagem, neste filme, pode ser pensada como produtora de um efeito melancólico.

The text proposes a study, based on Psychoanalytical theory, about the film Citizen Kane, by Orson Welles, touching upon some aspects related to melancholy. It is about regarding some parts of the movie context (script, soundtrack, editing), as well as the author's biography and the social context as social devices that award importance to the idea of the impossibility of mourning over a beloved object. Beyond the classic symptoms attributed to melancholy, the emphasis here lies on the process of loss described by Freud in 'Mourning and Melancholy' (1917 [1915]). The film makes us reflect on how much what is inherited can be paradoxically referred to a certain loss. Kane the character, in his childhood, inherits a fortune at the same time that he loses the possibility of living with his parents; thus, what he doesn't take from home (the sledge Rosebud) is what accompanies him for the rest of his life, as a significant, linked to the abandonment. The editing, one of the aspects of the movie analysis, is analyzed in more detail because it was considered, by Welles himself, as the main element of a movie masterpiece. Another proposition presented in this article is the idea that the editing, in this film, can also be thought as producing a melancholic effect.