Pigment granule migration and phototransduction are triggered by separate pathways in fly photoreceptor cells

AbstractWe have investigated the role of calcium in the regulation of pigment granule migration in photoreceptors of the semi-terrestrial crab, Sesarma cinereum. Isolated crab eyes (eyecup plus eyestalk) were maintained in crustacean Ringer either prepared normally or calcium-free plus 50 mM EGTA. Pigment granule movement was indirectly observed by monitoring reflectance from the eye during light stimuli using intracellular optical physiological techniques. Electroretinograms (ERGs) were also measured during light stimuli. EGTA treatment caused gradual loss of centripetal migration of pigment granules (normally leading to pupillary closure), and photoreceptors eventually became locked in the open-pupil, dark-adapted state despite repeated stimuli. In contrast, ERG responses continued throughout EGTA treatment, although the size and shape ofthe response was altered. Normal ERG responses and pigment granule movements returned after replacing EGTA-Ringer with normal-calcium medium. These results suggest that centripetal migration of pigment granules in crustacean photoreceptors requires calcium.

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Defective Pigment Granule Biogenesis and Aberrant Behavior Caused by Mutations in the Drosophila AP-3β Adaptin Gene ruby

Genetics ◽

10.1093/genetics/155.1.213 ◽

2000 ◽

Vol 155 (1) ◽

pp. 213-223

Author(s):

Doris Kretzschmar ◽

Burkhard Poeck ◽

Helmut Roth ◽

Roman Ernst ◽

Andreas Keller ◽

...

Keyword(s):

Protein Trafficking ◽

Coat Color ◽

Retinal Pigment ◽

Skin Pigmentation ◽

Pigment Granule ◽

Adaptor Protein ◽

Photoreceptor Cells ◽

Cell Types ◽

Eye Color ◽

Pigment Granules

Abstract Lysosomal protein trafficking is a fundamental process conserved from yeast to humans. This conservation extends to lysosome-like organelles such as mammalian melanosomes and insect eye pigment granules. Recently, eye and coat color mutations in mouse (mocha and pearl) and Drosophila (garnet and carmine) were shown to affect subunits of the heterotetrameric adaptor protein complex AP-3 involved in vesicle trafficking. Here we demonstrate that the Drosophila eye color mutant ruby is defective in the AP-3β subunit gene. ruby expression was found in retinal pigment and photoreceptor cells and in the developing central nervous system. ruby mutations lead to a decreased number and altered size of pigment granules in various cell types in and adjacent to the retina. Humans with lesions in the related AP-3βA gene suffer from Hermansky-Pudlak syndrome, which is caused by defects in a number of lysosome-related organelles. Hermansky-Pudlak patients have a reduced skin pigmentation and suffer from internal bleeding, pulmonary fibrosis, and visual system malfunction. The Drosophila AP-3β adaptin also appears to be involved in processes other than eye pigment granule biogenesis because all ruby allele combinations tested exhibited defective behavior in a visual fixation paradigm.

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Light-induced pigment granule migration in the retinular cells of Drosophila melanogaster. Comparison of wild type with ERG-defective mutants.

The Journal of General Physiology ◽

10.1085/jgp.77.2.155 ◽

1981 ◽

Vol 77 (2) ◽

pp. 155-175 ◽

Cited By ~ 34

Author(s):

M V Lo ◽

W L Pak

Keyword(s):

Drosophila Melanogaster ◽

Transient Receptor Potential ◽

Light Stimulus ◽

Strong Support ◽

Pigment Granule ◽

Receptor Potential ◽

Temperature Sensitive ◽

Experimental Conditions ◽

Trp Mutant ◽

Pigment Granule Migration

The dependence of pigment granule migration (PGM) upon the receptor potential was examined using several strains of electroretinogram (ERG)-defective mutants of Drosophila melanogaster. The mutants that have a defective lamina component but a normal receptor component of the ERG (no on-transient A [nonA] and tan) exhibited normal pigment granule migration. The mutants that have very small or no receptor potentials (certain no receptor potential A [norpA] alleles), on the other hand, exhibited no PGM. In the case of the temperature-sensitive norpA mutant, norpAH52, normal PGM was present at 17 degrees but not at 32 degrees C or above, corresponding to its electrophysiological phenotype. In the transient receptor potential (trp) mutant, whose receptor potential decays to the baseline within a few seconds during a sustained light stimulus, the pigment granules initially moved close to the rhabdomere when light was turned on but moved away after about 5 s during a sustained light stimulus. All these results lend strong support to the notion that PGM is initiated by a light-evoked depolarization of the receptor membrane, i.e., the receptor potential. However, under certain experimental conditions, the receptor potentials failed to induce PGM in the trp mutant. The depolarization of the receptor, thus, appears to be closely associated with PGM but is not a sufficient condition for PGM.

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Calcium Homeostasis in Fly Photoreceptor Cells

Advances in Experimental Medicine and Biology - Photoreceptors and Calcium ◽

10.1007/978-1-4615-0121-3_32 ◽

2002 ◽

pp. 539-583 ◽

Cited By ~ 7

Author(s):

Johannes Oberwinkler

Keyword(s):

Calcium Homeostasis ◽

Photoreceptor Cells ◽

Fly Photoreceptor

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Calcium-independent regulation of pigment granule aggregation and dispersion in teleost retinal pigment epithelial cells

Journal of Cell Science ◽

10.1242/jcs.109.1.33 ◽

1996 ◽

Vol 109 (1) ◽

pp. 33-43

Author(s):

C. King-Smith ◽

P. Chen ◽

D. Garcia ◽

H. Rey ◽

B. Burnside

Keyword(s):

Intracellular Calcium ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Pigment Granule ◽

Retinal Pigment Epithelial Cells ◽

Rod Photoreceptor ◽

Rpe Cells ◽

Pigment Granules ◽

Pigment Granule Migration

In the eyes of teleosts and amphibians, melanin pigment granules of the retinal pigment epithelium (RPE) migrate in response to changes in light conditions. In the light, pigment granules disperse into the cells' long apical projections, thereby shielding the rod photoreceptor outer segments and reducing their extent of bleach. In darkness, pigment granules aggregate towards the base of the RPE cells. In vitro, RPE pigment granule aggregation can be induced by application of nonderivatized cAMP, and pigment granule dispersion can be induced by cAMP washout. In previous studies based on RPE-retina co-cultures, extracellular calcium was found to influence pigment granule migration. To examine the role of calcium in regulation of RPE pigment granule migration in the absence of retinal influences, we have used isolated RPE sheets and dissociated, cultured RPE cells. Under these conditions depletion of extracellular or intracellular calcium ([Ca2+]o, [Ca2+]i) had no effect on RPE pigment granule aggregation or dispersion. Using the intracellular calcium dye fura-2 and a new dye, fura-pe3, to monitor calcium dynamics in isolated RPE cells, we found that [Ca2+]i did not change from basal levels when pigment granule aggregation was triggered by cAMP, or dispersion was triggered by cAMP washout. Also, no change in [Ca2+]i was detected when dispersion was triggered by cAMP washout in the presence of 10 microM dopamine, a treatment previously shown to enhance dispersion. In addition, elevation of [Ca2+]i by addition of ionomycin neither triggered pigment movements, nor interfered with pigment granule motility elicited by cAMP addition or washout. Since other studies have indicated that actin plays a role in both pigment granule dispersion and aggregation in RPE, our findings suggest that RPE pigment granule migration depends on an actin-based motility system that is not directly regulated by calcium.

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