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At least 19 recordsLinked to original sources
PubMed1979

Hormone-induced pigment translocations in amphibian dermal iridophores, in vitro: changes in cell shape.

Hormone-induced pigment translocation studies were conducted at both the light and electron microscopic levels on cultured dermal iridophores from the Mexican leaf frog, Pachymedusa dacnicolor. Two distinct types of dermal iridophores were characterized which differed in (1) their in vivo locations, (2) their overall morphologies in vitro, (3) their responses to alpha-MSH, ACTH, c-AMP or theophylline, (4) their physical alterations of light, and (5) certain ultrastructural features. One iridophore (Type I) was found to be physiologically responsive to the above hormones or agents by a reversible retraction of cellular processes and a thickening of the cell body, an event which is inhibited by cytochalasin B. The other iridophore (Type II) appeared to be unresponsive. Type I iridophores contain cube-like pigmentary organelles, refractosomes, while Type II iridophores contain larger, bar-shaped refractosomes. In addition, both iridophore types contain 60 and 100 A microfilaments as well as microtubules. By in large, micorfilaments were found within microvilli, beneath and parallel to the plasma membrane and in the perinuclear region. Occasionally, bundles of 100 A microfilaments were found between layers of refractosomes in Type I iridophores. These results are discussed in relation to hormone-induced changes in cell shape.

Actins↗
PubMed2004

The role of muscarinic receptors and intracellular Ca2+ in the spectral reflectivity changes of squid iridophores.

In this paper we describe changes in spectral reflectivity of the light reflectors (iridophores) of the squid Alloteuthis subulata. The spectral changes that can be seen in living squid, can also be brought about by superfusing whole skin preparations with acetylcholine (ACh) (20 micro mol l(-1)) and muscarine (30 micro mol l(-1)) but not nicotine (up to 50 mmol l(-1)), suggesting that cholinergic muscarinic receptors are involved. Changing the osmolarity of the external solution had no effect on spectral reflectivity. To study the iridophores at the cellular level, iridophores were isolated enzymatically. Lucifer Yellow filled the iridophores uniformly, showing cellular individuality. Isolated iridophore cells were loaded with Fura-2 AM and cytoplasmic Ca(2+) was recorded ratiometrically. Intracellular Ca(2+) (resting concentration at 66.16 nmol l(-1)) increased transiently after addition of ACh (50 micro mol l(-1)), muscarine (25 micro mol l(-1)), but not nicotine (up to 5 mmol l(-1)). Ca(2+) also increased when superfused with potassium chloride (10 mmol l(-1)) and caffeine (2.5 mmol l(-1)). Hypo- and hyperosmotic solutions had no effects on the cytoplasmic Ca(2+). By presenting direct evidence that iridophores are polarised cellular structures containing Ca(2+) stores and that they are activated via cholinergic muscarinic receptors, we demonstrate that Ca(2+) is involved in the reflectivity changes of the iridophores of A. subulata. Specimens were prepared for transmission electron microscopy. It was found that the orientations of the plates with respect to the skin surface are in good agreement with the expected orientations based on the prediction that the iridophores act as multilayer reflectors.

Acetylcholine↗
PubMed1990

Physiological color change in squid iridophores. I. Behavior, morphology and pharmacology in Lolliguncula brevis.

Cephalopods generally are thought to have only static iridophores, but this report provides qualitative and quantitative evidence for active control of certain iridescent cells in the dermis of the squid Lolliguncula brevis. In vivo observations indicate the expression of iridescence to be linked to agonistic or reproductive behavior. The neuromodulator acetylcholine (ACh) induced dramatic opitcla changes in active iridophores in vitro, whereas ACh had little effect on passive iridophores elsewhere in the mantle skin. Bath application of physiological concentrations of ACh (10(-7)M to 10(-6)M) to excised dermal skin layers transformed the active iridophores from a non-reflective diffuse blue to brightly iridescent colors, and this reaction was reversible and repeatable. The speed of change to iridescent in vitro corresponded well to the speed of changes in the living animal. Pharmacological results indicate the presence of muscarinic receptors in this system and that Ca++ is a mediator for the observed changes. Although ACh is present in physiological quantities in the dermal iridophore layer, it is possible that ACh release is not controlled directly by the nervous system because electrophysiological stimulation of major nerves in the periphery resulted in no iridescence in L. brevis; nor did silver staining or transmission electron microscopy reveal neuronal elements in the iridophore layer. Thus, active iridophores may be controlled by ACh acting as a hormone.

Acetylcholine↗
PubMed1974

Fine structural demonstration of ordered arrays of cytoplasmic filaments in vertebrate iridophores. A comparative survey.

Thin and thick sections of both physiologically active and physiologically passive iridophores from a range of vertebrate species have been examined by electron microscopy at 60 kV and at 1,000 kV. All iridophores studied have been found to contain 65-A filaments linking successive crystals in their parallel stacks; their orientation in the cell is shown in stereo pairs of 0.25-microm sections obtained from high voltage microscopy. In addition, several of the physiologically passive iridophores contain 100-A filaments in varying numbers. It is suggested that the thin filaments might be iridophore actin and play a role in the movement of iridophore components, and that the 100-A filaments might play a cytoskeletal role in the iridophores in which they occur.

Animals↗
PubMed2001

Reflective properties of iridophores and fluorescent 'eyespots' in the loliginid squid Alloteuthis subulata and Loligo vulgaris.

Observations were made of the reflective properties of the iridophore stripes of the squid Alloteuthis subulata and Loligo vulgaris, and the likely functions of these stripes are considered in terms of concealment and signalling. In both species, the mantle muscle is almost transparent. Stripes of iridophores run along the length of each side of the mantle, some of which, when viewed at normal incidence in white light, reflect red, others green or blue. When viewed obliquely, the wavebands best reflected move towards the blue/ultraviolet end of the spectrum and their reflections are almost 100% polarised. These are properties of quarter-wavelength stacks of chitin and cytoplasm, predicted in theoretical analyses made by Sir A. F. Huxley and Professor M. F. Land. The reflecting surfaces of the individual iridophores are almost flat and, in a given stripe, these surfaces are within a few degrees of being parallel. Both species of squid have conspicuous, brightly coloured reflectors above their eyes. These 'eyespots' have iridescent layers similar to those found on the mantle but are overlaid by a green fluorescent layer that does not change colour or become polarised as it is viewed more obliquely. In the sea, all reflections from the iridophore stripes will be largely confined to the blue-green parts of the spectrum and all reflections in other wavebands, such as those in the red and near ultraviolet, will be weak. The functions of the iridophores reflecting red at normal incidence must be sought in their reflections of blue-green at oblique angles of incidence. These squid rely for their camouflage mainly on their transparency, and the ventral iridophores and the red, green and blue reflective stripes must be used mainly for signalling. The reflectivities of some of these stripes are relatively low, allowing a large fraction of the incident light to be transmitted into the mantle cavity. Despite their low reflectivities, the stripes are very conspicuous when viewed from some limited directions because they reflect light from directions for which the radiances are much higher than those of the backgrounds against which they are viewed. The reflective patterns seen, for example, by neighbouring squid when schooling depend on the orientation of the squid in the external light field and the position of the squid relative to these neighbours.

Animal Communication↗
PubMed2026

Asymmetric Functional Divergence of alx4a and alx4b in Iridophore Differentiation and Cranial Development in Nile Tilapia.

Neural crest cells give rise to the craniofacial skeleton and multiple pigment cell lineages, yet how duplicated developmental regulators partition their ancestral functions after teleost-specific whole-genome duplication remains unclear. Here, we employed CRISPR/Cas9 to generate alx4a and alx4b single and double mutants in Nile tilapia (Oreochromis niloticus). By integrating phenotype, skeleton, transcriptome, quantitative PCR, and AlphaFold-based structural modeling analyses, we revealed their functional divergence. Loss of alx4a caused a regionally restricted reduction in iridophore-derived reflectance and abnormal cranial morphology, whereas alx4b single mutants showed no obvious phenotype under the conditions examined. By contrast, double mutants exhibited an almost complete loss of iridophore-derived structural coloration and substantially more severe cranial defects, accompanied by reduced calcein labeling in the opercular region, consistent with altered cranial mineralization. Skin transcriptomic and quantitative PCR analyses revealed marked downregulation of pnp4a and tfec, which are associated with iridophore differentiation and coloration, whereas no significant expression differences were detected for the iridophore survival-related genes ltk and mpv17. AlphaFold2-assisted HDOCK protein-DNA modeling yielded more favorable docking metrics for Alx4a than for Alx4b with the pnp4a promoter, supporting a potential Alx4a-pnp4a promoter interaction that requires experimental validation. In contrast, no significant genotype-dependent differences were detected in the measured abundance of melanophores, xanthophores, or erythrophores, and no obvious difference in gross dorsal-fin spine formation was observed under the conditions examined. Together, these findings reveal unequal functional contributions of alx4a and alx4b, with alx4a acting as the dominant paralog in iridophore-associated structural coloration and both paralogs contributing unequally to cranial development, and support pnp4a as a candidate downstream gene associated with Alx4a activity.

Animals↗
PubMed1976

Electron microscopy of two types of reflecting chromatophores (iridophores and leucophores) in the guppy, Lebistes reticulatus Peters.

Reflecting chromatophores in the integument of the guppy, Lebistes reticulatus Peters, are of two distinct types, iridophores and leucophores. The iridophores are smaller and fixed, producing a metallic iridescent color. The cytoplasmic organelles involved in the coloration of iridophores are the reflecting platelets, as in the iridophores of other fish and amphibian species on which earlier reports have been made. Spherical granules of pleiomorphic internal structure, quite variable in size but generally 0.2 mum to 1.0 mum in diameter, are also numerous in the iridophores. The nature of these granules remains unknown. The leucophores are larger, and highly dendritic; their pigment granules are migratory and they exhibit a dull whitish color. Pigment granules of the leucophores are spherical in form, varying from 0.5-0.8 mum in diameter, with a double membrane enclosing the internal fibrous materials. Melamine-treatment of the fish caused degenerative changes in the pigment granules and also the other cytoplasmic organelles of the leucophores, whereas the other kinds of chromatophores, including the iridiophores, remained intact. Some problems in general characterization and classification between these two types of chromatophores were discussed.

Animals↗
PubMed1990

Stimulation of cultured iridophores by amphibian ventral conditioned medium.

That the ventral integument of adult frogs (Rana pipiens) contains factor(s) that stimulate iridophore expression (adhesion, morphologic appearance, proliferation) was demonstrated on iridophores derived from tadpoles of R. pipiens and Pachymedusa dacnicolor, and maintained in primary culture in a growth medium based upon Leibovitz's L-15. Experimental growth medium (VCM) conditioned by a one-hour exposure to pieces of ventral skin of adult R. pipiens induced iridophores to assume a broad and stellate appearance, to form confluent sheets, and to proliferate over a nine-day period. Iridophores in control medium assumed long thin profiles, detached easily, and exhibited no signs of proliferation. Unknown cells containing reflecting platelets and unusual other organelles appeared uniquely in chromatophore cultures of P. dacnicolor in VCM. The intense stimulation of iridophore expression in VCM is consistent with the known inhibitory effect of this medium on melanization and with its purported role in the determination of dorsal/ventral pigment patterns of amphibians. The results are discussed in terms of a prevailing theory about pigment cell origins and development.

Amphibians↗
PubMed1995

A transmission electron microscopic (TEM) method for determining structural colors reflected by lizard iridophores.

Iridescent tissue colors are thought to be produced by iridophores through the optical phenomenon of thin-layer interference. Land and others have shown that structural features, predominantly reflecting platelet width and the cytoplasmic spacing between layers of platelets, determine the wavelength of light maximally reflected by this mechanism in iridophores. Some researchers have used interference microscopy to estimate these structural parameters, but the most direct measurement technique should be transmission electron microscopy (TEM). Transmission electron microscopy (TEM) has associated processing artifacts (particularly cytoplasmic shrinkage) that preclude direct measurement of ultrastructure, but if a number of assumptions are made, reflected wavelengths can be predicted. A thin-layer interference model and its associated assumptions were tested using TEM measurements of iridophores from several brightly colored tissues of each of three lizards (Sceloporus jarrovi, S. undulatus erythrocheilus, and S. magister). In all the instances examined when the contribution of the pigments present were accounted for, tissue color corresponded with predicted iridophore reflectances from the model. Finally, if the model and its assumptions are assumed to be correct, the amount of iridophore cytoplasmic shrinkage as a result of TEM processing can be calculated.

Animals↗
PubMed1982

Changes in spectral reflexions from the iridophores of the neon tetra.

1. The iridescent stripe of the freshwater teleost, the neon tetra, changes from green in the daytime to violet-blue at night. 2. Spectral reflectance measurements were used to follow these colour changes. 3. Light causes a shift in reflectance to longer wavelengths in living fish and in isolated tissue from the lateral stripe. The change is reversed in darkness. 4. The spectral reflectance shifts to longer wavelengths when the fish is disturbed in darkness. No such colour changes were seen in fishes kept alive in 10(-4) M-reserpine. 5. Hypotonic Ringer solution causes a reflectance shift to longer wavelengths and hypertonic solution causes a shift to shorter wavelengths. 6. The iridescent reflexions from the lateral stripe which is continued across the iris originate from iridophores in the dermis. These iridophores contain regular stacks of broad, double-sided hexagonal plates that are about 10 nm thick. Each plate is contained within a pouch in the cytoplasm and is separated from its neighbour by approximately one quarter the wavelength of light. 7. A distinction is drawn between the physiologically active iridophores in the lateral stripe and iris that have broad hexagonal crystal plates which are very thin and the physiologically inactive iridophores that are also found in the iris, but in addition are found on the flanks below the lateral stripe, and on the head. These iridophores contain hexagonal crystals that are usually narrower than the active type, but are about 60-100 nm thick.

Animals↗
PubMed1990

Physiological color change in squid iridophores. II. Ultrastructural mechanisms in Lolliguncula brevis.

Evidence is presented that changes in the optical properties of active iridophores in the dermis of the squid Lolliguncula brevis are the result of changes in the ultrastructure of these cells. At least two mechanisms may be involved when active cells change from non-iridescent to iridescent or change iridescent color. One is the reversible change of labile, detergent-resistant proteinaceous material within the iridophore platelets, from a contracted gel state (non-iridescent) to an expanded fluid or sol state when the cells become iridescent. The other is a change in the thickness of the platelets, with platelets becoming significantly thinner as the optical properties of the iridophores change from non-iridescent to iridescent red, and progressively thinner still as the observed iridescent colors become those of shorter wavelengths. Optical change from Rayleigh scattering (non-iridescent) to structural reflection (iridescent) may be due to the viscosity change in the platelet material, with the variations in observed iridescent colors due to changes in the dimensions of the iridophore platelets.

Acetylcholine↗
PubMed1992

Adrenergic mechanisms associated with the movement of platelets in iridophores from the freshwater goby, Odontobutis obscura.

1. Cultured iridophores from the freshwater goby, Odontobutis obscura, were used to investigate adrenergic mechanisms of movement of platelets in the iridophores. 2. Norepinephrine, which was assumed to be the transmitter of the iridophore nerves, induced dispersion of platelets within the cells. 3. The effect of norepinephrine was inhibited by an alpha-adrenergic antagonist, yohimbine, but not by a beta-adrenergic antagonist, propranolol. 4. Isoproterenol, a beta-adrenergic agonist, failed to bring about aggregation of platelets. 5. Forskolin, an activator of adenylate cyclase, was effective in inducing aggregation of platelets. 6. 8-Br-cAMP caused the aggregation of platelets and inhibited the norepinephrine-induced dispersion of platelets. 7. It appears that the adrenoceptors of the iridophores of this species are solely of the alpha type; they mediate the dispersion of platelets; and an increase in intracellular levels of cAMP induces the aggregation of platelets.

Adrenergic alpha-Antagonists↗
PubMed2006

Ultrastructure of the skin melanophores and iridophores in paddlefish, Polyodon spathula.

The ultrastructure of melanophores and iridophores of Polyodon spathula has been examined by transmission electron microscopy. In the skin, two types of chromatophores, melanophores and iridophores were founded. Melanophores were localized both in epidermis and dermis. Epidermal melanophores were present on the dorsal region of the trunk, sides, outer surface of the operculum and rostrum. Iridophores were founded in the dermis from ventral skin. The cytoplasm of iridophores is filled with reflecting platelets with variable orientation. The length of the long axis of the platelets varies from 1 to 2.10 microm.

Animals↗
PubMed1975

Biochemical characterization of crystals from the dermal iridophores of a chameleon Anolis carolinensis.

The biochemical characteristics of dermal iridophore crystals from Anolis carolinensis have been investigated. Iridophores isolated by collangenase-hyaluronidase treatment were sonicated and their contents fractionated through sucrose. Pure iridophore crystals so obtained were examined by chromatography and electron diffraction. They were found to be pure hydrated crystalline form. The suggestion is made that the subcrystalline structure of this guanine does not play a role in color production by the iridophore.

Animals↗
PubMedDate not supplied

Ultrastructural observations of motile iridophores from the freshwater goby, Odontobutis obscura.

The ultrastructure of "motile" iridophores of Odontobutis obscura and the changes in cell shape related to the motility were studied with electron microscopy. Various structural details were revealed by this method, and their importance is discussed. Of particular interest were the abundant microfilaments observed in the cortical cytoplasm. Cross-sectional profiles of iridophores showed that, in an iridophore in the dendritic state, the platelets were scattered randomly throughout the centrosphere and its processes, so that the centrosphere appeared to be rather flat. In the punctate state, the platelets were gathered, in groups or in stacks with regular arrangements, in the centrosphere, which appeared to be ovoid in shape. The most notable finding was that, at this time, the processes from which the platelets were lost remained there without retracting. The results indicates clearly that the motility of the goby iridophores involves the migration of platelets within the fixed contour of each cell and that no amoeboidal changes in the shapes of the cells occur.

Animals↗
PubMed2006

Light-sensitive motile iridophores and visual pigments in the neon tetra, Paracheirodon innesi.

Although motile iridophores in the longitudinal stripes of neon tetra skin are under control of the sympathetic nervous system, they also respond to light directly and show circadian color changes. Using neon tetra skin, we found that the photoresponse of iridophores depends on light intensity, and that light near 500 nm is most effective. RT-PCR demonstrated the expression of mRNAs encoding rhodopsin and two kinds of cone opsins (Pi-green1 and Pi-green2) in neon tetra skin where the light-sensitive iridophores exist. These mRNAs are also expressed in the lateral eyes. The cone opsin genes, Pi-green1 and Pi-green2, show high similarity with the g101 and g103 genes of unique green cone opsins (belonging to the MWS/LWS group) of the blind Mexican cavefish. These results show that Pi-green1, Pi-green2, and/or rhodopsin may play important roles in the photoresponse of neon tetra iridophores, which are most sensitive to light near 500 nm.

Animals↗
PubMed1992

Changes in the ventral dermis and development of iridophores in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis: an ultrastructural study.

The ultrastructural changes that take place in the ventral dermis along with the development of iridophores were examined in the anadromous sea lamprey, Petromyzon marinus, during metamorphosis. There is a disruption of all components of the ventral dermis and a reformation that results in a structure very similar to that prior to metamorphosis. Although not a dermal component, a layer of iridophores develops directly beneath the dermis during late metamorphosis. The dermal endothelium is lost by mid metamorphosis (stage 4) and the highly organized collagenous lamellae making up the bulk of the dermis become disrupted by the migration of fibroblasts into the region. Many of these fibroblasts are involved in the degradation of the lamellae. By stage 5 of metamorphosis some fibroblasts become highly active collagen synthesizing cuboidal shaped cells that align to form a layer above the reformed dermal endothelium. New lamellae are formed by these cuboidal cells which then divide and migrate into the lamellae where they assume the characteristic attenuated appearance of fibroblasts in the adult dermal lamellae region. Iridophores first appear during stage 5 directly beneath the dermal endothelium. Reflecting platelets develop from double membraned vesicles associated with the Golgi apparatus. By late metamorphosis, stacks of trapezoidal shaped platelets fill the cytoplasm of the iridophores. The significance of the changes in the dermis during metamorphosis are discussed. This work is part of a continuing series of studies on the connective tissues in the anadromous sea lamprey.

Animals↗
PubMed1992

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia: Anura: Hyperoliidae) to its arid environment. VI. The iridophores in the skin as radiation reflectors.

Hyperolius viridiflavus possesses one complete layer of iridophores in the stratum spongiosum of its skin at about 8 days after metamorphosis. The high reflectance of this thin layer is almost certainly the result of multilayer interference reflection. In order to reflect a mean of about 35% of the incident radiation across a spectrum of 300-2900 nm only 30 layers of well-arranged crystals are required, resulting in a layer 10.5 microns thick. These theoretical values are in good agreement with the actual mean diameter of single iridophores (15.0 +/- 3.0 microns), the number of stacked platelets (40-100) and the measured reflectance of one complete layer of these cells (32.2 +/- 2.3%). Iridescence colours typical of multilayer interference reflectors were seen after severe dehydration. The skin colour turned from white (0-10% weight loss) through a copper-like iridescence (10-25% weight loss) to green iridescence (25-42%). In dry season state, H. viridiflavus needs a much higher reflectance to cope with the problems of high solar radiation load during long periods with severe dehydration stress. Dry-adapted skin contains about 4-6 layers of iridophores. The measured reflectance (up to 60% across the solar spectrum) of this thick layer (over 60 microns) is not in keeping with the results obtained by applying the multilayer interference theory. Light, scattered independently of wavelength from disordered crystals, superimposes on the multilayer-induced spectral reflectance. The initial parallel shift of the multilayer curves with increasing thickness and the almost constant ("white") reflectance of layers exceeding 60 microns clearly point to a changing physical basis with increasing layer thickness.

Acclimatization↗