Body colors and algal distribution in the acoel flatworm Convolutriloba longifissura: histology and ultrastructure

Convolutriloba longifissura is a red flatworm with white dots that harbors unicellular green algae within its body. The red pigment of the flatworm that is present in round cells is soluble in ethanol or acetone, whereas the white pigment contained in the crystalline (retractile) platelets of amoeboid-shaped cells is soluble in 1% NH4OH. These two types of pigment cells form the body coloration and are probably involved in light protection of the algal symbionts, as many algal cells are distributed beneath the body wall and some are in the highly vacuolated parenchyma. The ultrastructural features of these cells suggest a close relationship with Tetraselmis spp. The morphology of sagittocysts within the mantle is also described by means of scanning and transmission electron microscopy.     

The ultrastructure of the nauplius eye ofSapphirina (Crustacea: Copepoda)

Summary The ultrastructure of the specialized nauplius eye of three species of the copepod genusSapphirina was investigated. The gross morphology described earlier (Elofsson, 1966a) was confirmed. The ventral cup is covered by a red pigment and the lateral cups by a red and a black pigment. The ultrastructural configuration of the pigment granules was found to differ in the two kinds of pigment cells. The black pigment cell, moreover, contains a large number of transversely banded fibrils and is able to produce reflecting crystals. The pigment granules of the black pigment cell show a variation in electron density. An intimate connexion exists between the black pigment cell and large retinula cells in the lateral cups, indicating an exchange of material. The tapetal cells present in all three cups form crystal platelets contained in two sets of membranes. It is suggested that the ventral cup and part of the lateral cups function as thePecten-eye (Land, 1965). The rhabdomeres of the retinula cells are composed of microvilli measuring 400 Å. The orientation of these seems to exclude polarotactic behaviour. The ventral cup and the four small cells of the lateral cups contain some retinula cells with microvilli arranged parallel to the incoming light. The retinula cells further develop an intricate system of membrane-invaginations penetrating deep into the cell and associated with numerous mitochondria. Retinula cells of the ventral cup and part of the lateral cups contain clear portions filled with granular material only. Retinula and other cells contain attenuated mitochondria with parallel tubuli. The proximal lens in front of each lateral cup consists of one cell. A development from the conjunctival cells is suggested. The results are evaluated in terms of function and evolution.This work has been supported by a grant from the Swedish Natural Science Research Council (2760-2).     

Sub-cellular Localisation of the White/Scarlet ABC Transporter to Pigment Granule Membranes Within the Compound Eye of Drosophila Melanogaster

The white, scarlet, and browngenes of Drosophila melanogasterencode ABC transporters involved with the uptake and storage of metabolic precursors to the red and brown eye colour pigments. It has generally been assumed that these proteins are localised in the plasma membrane and transport precursor molecules from the heamolymph into the eye pigment cells. However, the immuno-electron microscopy experiments in this study reveal that the White and Scarlet proteins are located in the membranes of pigment granules within pigment cells and retinula cells of the compound eye. No evidence of their presence in the plasma membrane was observed. This result suggests that, rather than tranporting tryptophan into the cell across the plasma membrane, the White/Scarlet complex transports a metabolic intermediate (such as 3-hydroxy kynurenine) from the cytoplasm into the pigment granules. Other functional implications of this new finding are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure,histochemistry, ontogenetic development,and regeneration of the ocellus of Cladonema radiatum dujardin (cnidaria,hydrozoa, anthomedusae)

The ectodermal eyes, 45–55 μm in diameter, of the cnidarian hydrozoan Cladonema radiatum Dujardin possess a lens approximately 15 μm in diameter enveloped by an eyecup (retina). An overlying layer of intensely vacuolated distal process of the adjoining epithelial cells forms a transparent cornea. The eyecup is composed of three cell types: basal cells, melanin-containing pigment cells, and photoreceptor cells. The last two cell types occur in the ratio of approximately 2:1. Histogenesis of the eye both during ontogeny and regeneration is described from light and electron microscopic investigations. During ontogeny the cell types forming the retina are derived from a compact group of morphologically undifferentiated cells, but during regeneration a primordium is formed by regeneration cells. In both cases the lens is built from distal nonnucleated cytoplasmic portions pinched off from the pigment cells. The cornea is formed by distal lamellar processes of the ocellus adjoining the epithelial cells. Through EM-histochemical methods (silver impregnation and DOPA-oxidase reaction) the pigment of the chromatophores of the retina was identified as melanin.     

The compound eye of<Emphasis Type="Italic"> Scutigera coleoptrata</Emphasis> (Linnaeus, 1758) (Chilopoda: Notostigmophora): an ultrastructural reinvestigation that adds support to the Mandibulata concept

The lateral compound eye of Scutigera coleoptrata was examined by electron microscopy. Each ommatidium consists of a dioptric apparatus, formed by a cornea and a multipartite eucone crystalline cone, a bilayered retinula and a surrounding sheath of primary pigment and interommatidial pigment cells. With reference to the median eye region, each cone is made up of eight cone segments belonging to four cone cells. The nuclei of the cone cells are located proximally outside the cone near the transition area between distal and proximal retinula cells. The connection between nuclear region and cone segment is via a narrow cytoplasmic strand, which splits into two distal cytoplasmic processes. Additionally, from the nuclear region of each cone cell a single cytoplasmic process runs in a proximal direction to the basement membrane. The bilayered rhabdom is usually made up of the rhabdomeres of 9–12 distal retinula cells and four proximal retinula cell. The pigment shield is composed of primary pigment cells (which most likely secrete the corneal lens) and interommatidial pigment cells. The primary pigment cells underlie the cornea and surround, more or less, the upper third of the crystalline cone. By giving rise to the cornea and by functioning as part of the pigment shield these pigment cells serve a double function. Interommatidial pigment cells extend from the cornea to the basement membrane and stabilise the ommatidium. In particular, the presence of cone cells, primary pigment cells as well as interommatidial pigment cells in the compound eye of S. coleoptrata is seen as an important morphological support for the Mandibulata concept. Furthermore, the phylogenetic significance of these cell types is discussed with respect to the Tetraconata.     

Fine structure of a secondarily developed eye in the freshwater moss-mite,Hydrozetes lemnae (Coggi, 1899) (Acari: Oribatida)

Summary The lenticulus ofHydrozetes lemnae represents an eye composed of a single cuticular cornea underlain by flat extensions of epidermal cells, two pigment cells, and a pair of lamellated bodies. The latter consist of about 100 vertically arranged lamellae which are orientated longitudinally in the animal. The lamellated bodies are accompanied by glia cells. Two large fat body cells separate the paired components medially. Each lamellated body is connected to a perikaryon located in the brain. It is evident that these components are parts of photoneurons of the central nervous system. Their vertically directed extensions are dendritic branches, terminating under the cornea as lamellated bodies. It is assumed that these are the photosensitive parts of the two photoneurons which serve as receptor cells. The axon of each cell runs transversely through the brain and terminates in a small distinct optic neuropile close to the opposite perikaryon. Thus the resulting chiasma opticum comprises two axons only. The extraordinary composition of this eye corroborates the assumption that it is a secondary light sense organ.     

Rapid colour changes in Euglena sanguinea (Euglenophyceae) caused by internal lipid globule migration

The accumulation of red pigments, frequently carotenoids, under chronic stress is a response observed in diverse kinds of eukaryotic photoautotrophs. It is thought that red pigments protect the chlorophyll located underneath by a light-shielding mechanism. However, the synthesis or degradation of carotenoids is a slow process and this response is usually only observed when the stress is maintained over long periods of time. In contrast, rapid colour changes have been reported in the euglenophyte Euglena sanguinea. Here we study the ecophysiological process behind this phenomenon through chlorophyll fluorescence, and pigment, colour and ultrastructural analyses. Reddening in E. sanguinea was due to the presence of a large amount of free and esterified astaxanthin (representing 80% of the carotenoid pool). The process was highly dynamic, shifting from green to red in 8 min (and vice-versa in 20 min). This change was not due to de novo carotenogenesis, but to the relocation of cytoplasmic lipid globules where astaxanthin accumulates. Thus, red globules were observed to migrate from the centre of the cell to peripheral locations when exposed to high light. Globule migration seems to be so efficient that other classical photoprotective mechanisms are not operative in this species. Despite the presence and operation of the diadino-diatoxanthin cycle, non-photochemical quenching was almost undetectable. Since E. sanguinea forms extensive floating colonies, reddening can be observed at a much greater scale than at the cellular level and the mechanism described here is one of the fastest and most dramatic colour changes attributable to photosynthetic organisms at cell and landscape level. In conclusion E. sanguinea shows an extremely dynamic and efficient photoprotective mechanism, based more on organelle migration than on carotenoid biosynthesis, which prevents excess light absorption by chlorophylls reducing the need for other protective processes related to energy dissipation.     

The structures of dorsal and ventral regions of a dragonfly retina

Summary The apposition eyes of the corduliid dragonfly Hemicordulia tau are each divided by pigment colour, facet size and facet arrangement into three regions: dorsal, ventral, and a posterior larval strip. Each ommatidium has two primary pigment cells, twenty-five secondary pigment cells, and eight receptor cells, all surrounded by tracheae which probably prevent light passing between ommatidia, and reduce the weight of the eye. Electron microscopy reveals that the receptor cells are of two types: small vestigial cells making virtually no contribution to the rhabdom, and full-size typical cells. The ventral ommatidia have a distal typical cell (oriented either horizontally or vertically), four medial typical cells, two proximal typical cells and one full-length vestigial cell. The dorsal ommatidia have only four full-length typical cells, and one distal and three vestigial full-length cells. The cross-section of dorsal rhabdoms is small and circular distally, but expands to a large three-pointed star medially and proximally. The tiered receptor arrangement in the ventral ommatidia is typical of other Odonata but the dorsal structure has not been fully described in other species. Specialised dorsal eye regions are typical of insects that detect others against the sky.     

灰茶尺蠖成虫复眼的超微结构及其明暗适应中的变化

【目的】明确灰茶尺蠖Ectropis grisescens成虫复眼的超微结构及其明暗适应中的变化,探究其调光机制。【方法】采用超景深显微镜测定了灰茶尺蠖成虫复眼的小眼数量、间角、直径和曲率半径等外部参数,并通过组织切片、光学显微镜和透射电子显微镜等技术观察了复眼的内部超微结构;通过光学显微镜观察了灰茶尺蠖成虫复眼在明暗环境中分别适应2 h后晶锥结构及色素颗粒的位置变化。【结果】灰茶尺蠖成虫复眼呈半球形,雌、雄虫单个复眼分别有2 502±105和3 123±78个小眼。小眼自远端至近端由角膜、晶锥、透明区构成的屈光层和由15个视网膜细胞构成的感光层组成。2个初级色素细胞包裹着晶锥,自角膜近端延伸至视网膜细胞核区的远端;每个小眼外围由6个次级色素细胞围绕,自角膜近端延伸至基膜;在透明区内14个视网膜细胞聚集成束(非感杆束),远端与晶锥束末端连接,在感光层内形成闭合型感杆束,延伸至第15个视网膜细胞(基部视网膜细胞)。在明暗适应时,灰茶尺蠖复眼的晶锥细胞间出现开闭,色素颗粒进行纵向位移,以适应外界的光强度的变化。【结论】灰茶尺蠖成虫复眼属于重叠像眼,感杆束为“14+1”模式;屏蔽色素颗粒的移...     

Ultrastructure of the eye of the amber snail Succinea putris (L.) (Gastropoda, Stylommatophora)]

The structure and some aspects of the development of the eye of Succinea putris were studied with the aid of the electron microscope. The eye is of the closed vesicle type and is composed of retina, cornea, vitreous body, lens and optic nerve. Three different types of cell are to be found in the retina: (1) the small elongated pigment cell with an avoid nucleus, many pigment granulae and short microvilli at the apical end of the cell; (2) the sensory cell type I with a large irregular nucleus, long microvilli, which extend to under the surface of the lens, a large number of light-cored vesicles, 700 A in diameter and the axon; (3) the elongated slender sensory cell type II with many dense cored vesicles, several pigment granulae in the distal region of the cell and short irregular microvilli at the apical end of the cell. This type is few in number. Two results of the study of the embryonic eye are described: the cornea cells differ from those in the adult eye in the nucleus-cytoplasm relation and the optic nerve is smaller than in the adult eye.     

Relations between pigmentation of the cornea and the number of epidermal melanophores in Rana temporaria L. larvae

The dynamics of the external cornea pigmentation in Rana temporaria L. larvae at the 22d developmental stage have been studied under conditions favourable for various course of certain morphological reactions in the pigment system. The cornea together with the surrounding skin is transferred on the dorsal surface of the larva body, and the piece of the dorsal surface skin is put instead of the cornea removed. When using the reciprocal transplantation method and preserving the organism's integrity (without disturbing melanocyte-stimulating source--namely, the hypophysis, and melatonine sources--namely, the pineal gland and the lateral eyes) the corneal pigmentation is observed on the background of perfect morphological reactions in the pigment system, while the larvae are maintained on the dark and light substrates, that is at various density of the pigment cells (120 larvae have been used). The pigmentation dynamics have been studied from the 6th up to the 20th day in total preparations. The epidermal melanophores density is estimated in 4 areas of each preparation. The melanin amount is estimated by means of the electron paramagnetic resonance-spectrometry according to the contents of free radicals expressed in relative units. A direct proportional dependence between the significantly higher melanin contents (1.5-fold) and a significantly quicker (1.5-fold) process of the corneal pigmentation is revealed, that agrees with an increasing number of the pigment cells per one unit of the body surface in the larvae maintained on the dark substrate. In the larvae maintained on the light substrate, the dependence is of a reverse character. It is probable that the factors forcing the pigmented cells, at cultivation the neural crest cells in vitro to reject from each other, affect the pigmentation of the larval cornea in vivo. If it is the case, the processes specific for the embryonal period, transgress during the cornea pigmentation at the larval stages of development.     

On the heredity of Y-linked color genes in Xiphophorus pygmaeus nigrensis Rosen (Pisces)

Summary The inheritance of two Y-linked colour genes of the Poecillid Xiphophorus pygmaeus nigrensis has been described. Males with the gene Fl (=flavus) posess a yellow colouration of the body whereas those with the gene Vfl (= venter flavus) only at the basis of the anal ray. These patterns depend on G-xanthophores, yellow pigment cells with colourless granulation (Öktay).Cross-breedings with X. maculatus and X. milleri cause an intensification of the patterns by increase of the number of the G-xanthophores and their transformation into xanthoerythrophores (colour cells with red granulation). Backcross males with X. maculatus inheriting Fl or Vfl show a red colouration of the whole body.These results may be explained by the theory of Kosswig, Gordon and Öktay of polygenic modifier systems. Their function is to regulate the number, the intensity and the grade of pigment cells, while the colour gene activates this process of establishing the pattern and determines the center of it. Modifiers in X. pygmaeus nigrensis changing G-xanthophores into xanthoerythrophores are below a genetic level or absent.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

A new mechanism in blue cone monochromatism

Blue cone monochromatism (BCM) is a rare X-linked colour vision disorder characterized by the absence of both red and green cone sensitivity. Most mutations leading to BCM fall into two classes of alterations in the red and green pigment gene array at Xq28. In one class the red and green pigment genes are inactivated by deletion in the locus control region. In the second class genetic rearrangements have created an isolated pigment gene that carries an inactivating point mutation. Here we describe a clinical case of BCM caused by a new mutation where exon 4 of an isolated red pigment gene has been deleted. The finding represents the first intragenic deletion yet described among red and green pigment genes. Received: 29 December 1995 / Revised: 30 May 1996     

Localization of iodopsin and rod-opsin immunoreactivity in the retina and pineal complex of the river lamprey,Lampetra japonica

Melano-macrophages in the head-kidney, spleen and liver of sea bass and gilthead seabream have been investigated by means of light and electron microscopy, histochemistry and phagocytic assays. The results demonstrate the presence of both free and clustered melano-macrophages (melano-macrophage centres), with similar ultrastructural features. These large cells are PAS-, hemosiderin-and melanin-positive, and contain large, alkaline-and acid phosphatase-positive lysosomes, whose reaction intensity depends on the amount of accumulated pigment. The relationship between the cytochemical features of these lysosomes and the capacity of the melano-macrophages to phagocytose bacteria and latex beads, has been studied. The large melanomacrophage centres have a capsule of flattened cells, whose ultrastructural and cytochemical features are similar to fibroblast-like reticular cells. Melanin is the main accumulated pigment. A subpopulation of head-kidney mononuclear phagocytes engulfs melanin associated with cell debris. The relationship between the origin of the melano-macrophage pigment and the ability of monocytes/macrophages to phagocytise the melanin from melanocytes, is considered. The origin and possible function of melano-macrophage centres are discussed.     

Molecular and functional studies of tilapia (Oreochromis mossambicus) NMDA receptor NR1 subunits

The Pin-tailed Manakin (Ilicura militaris) is a small, sexually dimorphic, frugivorous suboscine songbird (Pipridae; Passeriformes; Aves) endemic to the Atlantic Forest of Brazil. A variant individual of this species was recently described in which the red patches that characterise the male's Definitive plumage were replaced by orange-yellow ones. We show here that the pigments in the feathers of the colour variant are common dietary carotenoids (zeaxanthin, beta-cryptoxanthin), not carotenoids synthesised by birds, lending support to the suggestion that the individual is a colour mutant lacking the capability to transform yellow dietary pigments into the red pigments normally present in these feathers. By comparison, the yellow crown feathers of a close relative, the Golden-winged Manakin (Masius chrysopterus), contained predominantly endogenously produced epsilon-caroten-3'-ones. Surprisingly, the normal-coloured feathers of the male Pin-tailed Manakin owe their red hue to rhodoxanthin, an unusual carotenoid more commonly found in plants, rather than 4-keto-carotenoids typically found in red plumages and found lacking in previously characterised bird colour variants. The implication is that birds, like the tilapia fish, may be able to synthesise this unusual pigment endogenously from dietary precursors. A newly described carotenoid, 6-hydroxy-epsilon,epsilon-carotene-3,3'-dione, here named piprixanthin, present in the red feathers of the Pin-tailed Manakin, provides a plausible intermediate between epsilon,epsilon-carotene-3,3'-dione (canary-xanthophyll B), a bright yellow pigment found in this and other songbirds, and rhodoxanthin. It is apparent that pigeons (Columbidae, Columbiformes) also have the capability to produce rhodoxanthin, and a structurally related pigment, endogenously. The ability to synthesise rhodoxanthin might have arisen at least twice in birds.     

Light-induced, dark-reversible colour shifts in petals of Phlox

Flowers of some Phlox ( Phlox x paniculata L.) varieties undergo daily colour shifts, being blue in the early morning, turning red during the day, and returning to blue in the evening. The colour shift, which occurs only in the upper (adaxial) petal surfaces, is due to the daily changes in ambient light. In the laboratory, colour shifts could be induced by 2.5 h of ultraviolet, visible or far-red light and recorded by reflectance spectrophotometry.
There are indications that irradiations with different kinds of light cause qualitatively different colour shifts, and that thus more than one photoreceptor pigment and more than one primary light reaction may be involved. The presence of phytochrome was demonstrated in petals of white Phlox flowers by in vivo transmission spectrophotometry. It is therefore possible that colour shifts in coloured Phlox flowers are mediated by phytochrome. Possibly the movement of ions (e.g. hydrogen ions) into or out of the vacuole (where the visible pigments are located) is affected by light absorption in a pigment in the tonoplast.     

Identification of two types of melanocyte within the stria vascularis of the mouse inner ear

We have distinguished two types of melanocyte within the intermediate layer of the stria vascularis in the cochlea of normally pigmented mice: light and dark intermediate cells. The light intermediate cells are present in the stria from birth and have the typical appearance of a melanocyte. They are large and dendritic with electron-lucent cytoplasm containing numerous vesicles that show tyrosinase activity, and pigment granules in various stages of development. These granules have the ultrastructural and histochemical characteristics of premelanosomes and melanosomes. The light intermediate cells persist throughout life, but less frequently contain pigment in older animals. The dark intermediate cells, present only in adult mice, vary considerably in number and distribution between animals. Pigment granules, bound within an electron-dense acid phosphatase-rich matrix, form the main component of the dark intermediate cells. The intermediate cells may comprise either two distinct cell populations or different developmental stages of the same cell type; ultrastructural observations suggest the latter. In young mice, light intermediate cells contain the electron-dense matrices, which at later stages of development are found almost exclusively in dark cells. The dark intermediate cells contain few cell organelles other than pigment granules accumulated within lysosomal bodies and they often have pycnotic nuclei. These observations suggest that the dark intermediate cells are a degenerate form of the light intermediate cells. Clusters of melanosomes also occur in the basal cells, and to a much lesser extent in the marginal cells. These cells do not stain after incubation in DOPA, suggesting that they are not capable of melanin synthesis, and therefore probably acquire melanin by donation from adjacent melanocytes. Pigment clusters are also found within the spiral ligament at all stages of development.     

Ultrastructure of secretion in the atrial gland of a mollusc (Aplysia)

Extracts of the atrial gland of the sea hare Aplysia californiea (Mollusca) induce egg laying when injected into mature individuals. Since egg laying is controlled endogenously by a peptide secreted by neuroendocrine cells in the central nervous system, the relationship between the atrial gland and these central neurons has become an issue of interest. With the particular objective of examining secretory structures we undertook an ultrastructural study of the atrial gland and adjacent tissues. This study revealed that the atrial gland epithelium is composed of two major cell types: ‘goblet-like’ exocrine cells containing large electron-dense granules, and ciliated ‘capping cells’. A non-secretory, and possibly post-secretory, cell containing electron-lucent granules was noted. A region of the large hermaphroditic duct contiguous to the atrial gland, known as the red hemiduct, also displayed capping cells and secretory cells with large granules. The content of these granules is organized into crista-like condensations. The cell also contains iron-rich pigment inclusions.     

Cytoskeleton of retinular cells from the stomatopod,Gonodactylus oerstedii: possible roles in pigment granule migration

Retinular cells of the compound eyes of stomatopods (mantis shrimps) contain screening pigment granules that migrate radially in response to light. To clarify the role of the cytoskeleton in these movements, we have performed light microscopy and ultrastructural analyses of cytoskeletal organelles in retinular cells. Rhodamine phalloidin staining indicates that filamentous actin is a component of microvillar rhabdomeres and zonula adherens between retinular cells. Ultrastructural studies reveal three populations of microtubules in retinular cells that differ in their orientations and labilities to fixation. Two of these populations are oriented longitudinally in cells: the soma microtubules, found primarily in a column in the cell soma, and the more labile palisade microtubules, which extend alongside the palisade vacuole near the rhabdomere. The third, most labile microtubule population, and filaments 9–30 nm in diameter, are oriented radially in retinular cells, some within cytoplasmic bridges that span the palisade. The radial microtubules and filaments are appropriately oriented for participating in pigment granule migration. Determination of microtubule polarities in retinular cells by decoration with endogenous tubulin indicates that palisade and soma microtubules contain subpopulations having opposite polarity orientations, as has been observed in neuronal dendrites. In contrast, neighboring pigment cells contain microtubules uniformly oriented with minus ends towards the nucleus, as has been observed in most cell types studied.