Reconstructing the eyes of Urbilateria

Arendt, Detlev; Wittbrodt, Joachim

doi:10.1098/rstb.2001.0971

Cited by 191 publications

(184 citation statements)

References 144 publications

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“…In contrast, the morphological organization of the echinoid PRC system, as well as the arrangement of functional optic organs, differs considerably from that in other metazoans. In sea urchins, not even the simplest "proto-eye" is present in terms of a PRC being partially shielded by pigment and thus allowing for directional vision (15,30,31). In addition to the lack of a typical "eye-organ," the echinoid PRC arrangement in regard to the nervous system is also unique among metazoans.…”

Section: Discussionmentioning

confidence: 99%

Unique system of photoreceptors in sea urchin tube feet

Ullrich-Lüter

Dupont

Arboleda

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

134

160

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Different sea urchin species show a vast variety of responses to variations in light intensity; however, despite this behavioral evidence for photosensitivity, light sensing in these animals has remained an enigma. Genome information of the recently sequenced purple sea urchin (Strongylocentrotus purpuratus) allowed us to address this question from a previously unexplored molecular perspective by localizing expression of the rhabdomeric opsin Spopsin4 and Sp-pax6, two genes essential for photoreceptor function and development, respectively. Using a specifically designed antibody against Sp-Opsin4 and in situ hybridization for both genes, we detected expression in two distinct groups of photoreceptor cells (PRCs) located in the animal's numerous tube feet. Specific reactivity of the Sp-Opsin4 antibody with sea star optic cushions, which regulate phototaxis, suggests a similar visual function in sea urchins. Ultrastructural characterization of the sea urchin PRCs revealed them to be of a microvillar receptor type. Our data suggest that echinoderms, in contrast to chordates, deploy a microvillar, r-opsinexpressing PRC type for vision, a feature that has been so far documented only in protostome animals. Surprisingly, sea urchin PRCs lack any associated screening pigment. Indeed, one of the tube foot PRC clusters may account for directional vision by being shaded through the opaque calcite skeleton. The PRC axons connect to the animal internal nervous system, suggesting an integrative function beyond local short circuits. Because juveniles display no phototaxis until skeleton completion, we suggest a model in which the entire sea urchin, deploying its skeleton as PRC screening device, functions as a huge compound eye.evolution | electron microscopy | immunogold

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Section: Discussionmentioning

confidence: 99%

Unique system of photoreceptors in sea urchin tube feet

Ullrich-Lüter

Dupont

Arboleda

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

134

160

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“…3). These eyespots have been shown by morphological analyses to be rhabdomeric pigment cell cup photoreceptors (Brandenburger et al, 1973) that appear to have been lost by the echinoderm ancestors (Arendt and Wittbrodt, 2001). Lancelet and tunicate larvae contain both rhabdomeric and ciliary photoreceptor cells.…”

Section: Evolution Of Eyespots In Deuterostome Larvaementioning

confidence: 98%

“…Lancelet and tunicate larvae contain both rhabdomeric and ciliary photoreceptor cells. In lancelets, these are retained in the adult (Arendt and Wittbrodt, 2001), whereas in ascidians, the larvae have a pigmented ocellus and otolith (Swalla, 2006) that undergo programmed cell death at metamorphosis. Therefore, we hypothesize that the deuterostome ancestor had a feeding larva with anterior sensory photoreceptor cells that were evolutionarily lost in adults of the ambulacraria.…”

Section: Evolution Of Eyespots In Deuterostome Larvaementioning

confidence: 99%

Man is but a worm: Chordate origins

Brown

Prendergast

Swalla

2008

Genesis

112

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Summary: The origin of chordates remains one of the major puzzles of zoology, even after more than a century of intense scientific inquiry, following Darwin's ''Origin of Species''. The chordates exhibit a unique body plan that evolved from a deuterostome ancestor some time before the Cambrian. Molecular data gathered from phylogenetics and developmental gene expression has changed our perception of the relationships within and between deuterostome phyla. Recent developmental gene expression data has shown that the chordates use similar gene families and networks to specify their anterior-posterior, dorsal-ventral and left-right body axes. The anterior-posterior axis is similarly established among deuterostomes and is determined by a related family of transcription factors, the Hox gene clusters and Wnt signaling pathways. In contrast, the dorsalventral axis is inverted in chordates, compared with other nonchordate invertebrates, while still determined by expression of BMP signaling pathway members and their antagonists. Finally, left-right asymmetries in diverse deuterostomes are determined by nodal signaling. These new data allow revised, testable hypotheses about our earliest ancestors. We present a new hypothesis for the origin of the chordates whereby the expansion of BMP during dorsal-ventral patterning allowed the evolution of noneural ectoderm and pharyngeal gill slits on the ventral side. We conclude that ''Man is but a worm . . . ,'' that our chordate ancestors were worm-like deposit and/or filter feeders with pharyngeal slits, and an anterior tripartite unsegmented neurosensory region. genesis 46:605-613,

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“…Each photoreceptor type uses a separate phototransduction cascade. Rhabdomeric photoreceptors employ r-opsins and a phospholipase C cascade, whereas ciliary photoreceptors use c-opsins and a phosphodiesterase (PDE) cascade (2,3). In general, the dark pigment reduces photon scatter and orients the direction optimally sensitive to light.…”

mentioning

confidence: 99%

Assembly of the cnidarian camera-type eye from vertebrate-like components

Kozmík

Růžičková

Jonasova

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

119

113

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Animal eyes are morphologically diverse. Their assembly, however, always relies on the same basic principle, i.e., photoreceptors located in the vicinity of dark shielding pigment. Cnidaria as the likely sister group to the Bilateria are the earliest branching phylum with a well developed visual system. Here, we show that cameratype eyes of the cubozoan jellyfish, Tripedalia cystophora, use genetic building blocks typical of vertebrate eyes, namely, a ciliary phototransduction cascade and melanogenic pathway. Our findings indicative of parallelism provide an insight into eye evolution. Combined, the available data favor the possibility that vertebrate and cubozoan eyes arose by independent recruitment of orthologous genes during evolution.T he assembly of diverse animal eyes requires two fundamental building blocks, photoreceptors and dark shielding pigment. The function of photoreceptors is to convert light (stream of photons) into intracellular signaling. The photoreceptor cells (PRCs) are classified into two distinct types: rhabdomeric, characteristic of vision in invertebrate eyes; and ciliary, characteristic of vision in vertebrate eyes (1). In both ciliary and rhabdomeric PRCs, the seven-transmembrane receptor (opsin) associates with retinal to constitute a functional photosensitive pigment. Each photoreceptor type uses a separate phototransduction cascade. Rhabdomeric photoreceptors employ r-opsins and a phospholipase C cascade, whereas ciliary photoreceptors use c-opsins and a phosphodiesterase (PDE) cascade (2, 3). In general, the dark pigment reduces photon scatter and orients the direction optimally sensitive to light. The biochemical nature of the dark pigment appears more diverse than the phototransduction cascades used by the PRCs. Vertebrate eyes use melanin as their exclusive dark pigment. However, among invertebrates, pterins constitute the eye pigment in the polychaete Platynereis dumerilii (4), pterins and ommochromes are accumulated in eyes of Drosophila (5), and melanin is found rarely such as in the inverse cup-like eyes of the planarian, Dugesia (6).Cnidaria, the likely sister group to the Bilateria, constitute the earliest branching phylum containing a well developed visual system. For example, Cubozoa (known as ''box jellyfish'') have camera-type eyes with cornea, lens, and retina; unexpectedly, the cubozoan retina has ciliated PRCs that are typical for vertebrate eyes (7-9). Cubomedusae are active swimmers that are able to make directional changes in response to visual stimuli (10). The cubozoan jellyfish, Tripedalia cystophora (Fig. 1A), has four sensory structures called rhopalia that are equally spaced around the bell. In addition to two camera-type lens containing eyes at right angles to one another, each rhopalium has two pit-shaped and two slit-shaped pigment cup eyes (Fig. 1B). Thus, with six eyes located on each rhopalium, Tripedalia has 24 eyes altogether. Because the visual fields of individual eyes of the rhopalium partly overlap, Tripedalia (like other Cubomedusae) has an al...

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Reconstructing the eyes of Urbilateria

Cited by 191 publications

References 144 publications

Unique system of photoreceptors in sea urchin tube feet

Unique system of photoreceptors in sea urchin tube feet

Man is but a worm: Chordate origins

Assembly of the cnidarian camera-type eye from vertebrate-like components

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