1
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Brodrick E, Jékely G. Photobehaviours guided by simple photoreceptor systems. Anim Cogn 2023; 26:1817-1835. [PMID: 37650997 PMCID: PMC10770211 DOI: 10.1007/s10071-023-01818-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Revised: 07/29/2023] [Accepted: 08/01/2023] [Indexed: 09/01/2023]
Abstract
Light provides a widely abundant energy source and valuable sensory cue in nature. Most animals exposed to light have photoreceptor cells and in addition to eyes, there are many extraocular strategies for light sensing. Here, we review how these simpler forms of detecting light can mediate rapid behavioural responses in animals. Examples of these behaviours include photophobic (light avoidance) or scotophobic (shadow) responses, photokinesis, phototaxis and wavelength discrimination. We review the cells and response mechanisms in these forms of elementary light detection, focusing on aquatic invertebrates with some protist and terrestrial examples to illustrate the general principles. Light cues can be used very efficiently by these simple photosensitive systems to effectively guide animal behaviours without investment in complex and energetically expensive visual structures.
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Affiliation(s)
- Emelie Brodrick
- Living Systems Institute, University of Exeter, Stocker Road, Exeter, EX4 4QD, UK.
| | - Gáspár Jékely
- Living Systems Institute, University of Exeter, Stocker Road, Exeter, EX4 4QD, UK
- Centre for Organismal Studies, University of Heidelberg, 69120, Heidelberg, Germany
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2
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Schweikert LE, Bagge LE, Naughton LF, Bolin JR, Wheeler BR, Grace MS, Bracken-Grissom HD, Johnsen S. Dynamic light filtering over dermal opsin as a sensory feedback system in fish color change. Nat Commun 2023; 14:4642. [PMID: 37607908 PMCID: PMC10444757 DOI: 10.1038/s41467-023-40166-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 07/14/2023] [Indexed: 08/24/2023] Open
Abstract
Dynamic color change has evolved multiple times, with a physiological basis that has been repeatedly linked to dermal photoreception via the study of excised skin preparations. Despite the widespread prevalence of dermal photoreception, both its physiology and its function in regulating color change remain poorly understood. By examining the morphology, physiology, and optics of dermal photoreception in hogfish (Lachnolaimus maximus), we describe a cellular mechanism in which chromatophore pigment activity (i.e., dispersion and aggregation) alters the transmitted light striking SWS1 receptors in the skin. When dispersed, chromatophore pigment selectively absorbs the short-wavelength light required to activate the skin's SWS1 opsin, which we localized to a morphologically specialized population of putative dermal photoreceptors. As SWS1 is nested beneath chromatophores and thus subject to light changes from pigment activity, one possible function of dermal photoreception in hogfish is to monitor chromatophores to detect information about color change performance. This framework of sensory feedback provides insight into the significance of dermal photoreception among color-changing animals.
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Affiliation(s)
- Lorian E Schweikert
- Institute of the Environment, Department of Biological Sciences, Florida International University, North Miami, FL, 33181, USA.
- Biology Department, Duke University, Durham, NC, 27708, USA.
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, 28403, USA.
| | - Laura E Bagge
- Torch Technologies, Shalimar, FL, 32579, USA
- Air Force Research Laboratory/RWTCA, Eglin Air Force Base, FL, 32542, USA
| | - Lydia F Naughton
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, 28403, USA
| | - Jacob R Bolin
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, 28403, USA
| | | | - Michael S Grace
- College of Engineering and Science, Florida Institute of Technology, Melbourne, FL, 32901, USA
| | - Heather D Bracken-Grissom
- Institute of the Environment, Department of Biological Sciences, Florida International University, North Miami, FL, 33181, USA
- Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560, USA
| | - Sönke Johnsen
- Biology Department, Duke University, Durham, NC, 27708, USA
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3
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Structure and proteomic analysis of the crown-of-thorns starfish (Acanthaster sp.) radial nerve cord. Sci Rep 2023; 13:3349. [PMID: 36849815 PMCID: PMC9971248 DOI: 10.1038/s41598-023-30425-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Accepted: 02/22/2023] [Indexed: 03/01/2023] Open
Abstract
The nervous system of the Asteroidea (starfish or seastar) consists of radial nerve cords (RNCs) that interconnect with a ring nerve. Despite its relative simplicity, it facilitates the movement of multiple arms and numerous tube feet, as well as regeneration of damaged limbs. Here, we investigated the RNC ultrastructure and its molecular components within the of Pacific crown-of-thorns starfish (COTS; Acanthaster sp.), a well-known coral predator that in high-density outbreaks has major ecological impacts on coral reefs. We describe the presence of an array of unique small bulbous bulbs (40-100 μm diameter) that project from the ectoneural region of the adult RNC. Each comprise large secretory-like cells and prominent cilia. In contrast, juvenile COTS and its congener Acanthaster brevispinus lack these features, both of which are non-corallivorous. Proteomic analysis of the RNC (and isolated neural bulbs) provides the first comprehensive echinoderm protein database for neural tissue, including numerous secreted proteins associated with signalling, transport and defence. The neural bulbs contained several neuropeptides (e.g., bombyxin-type, starfish myorelaxant peptide, secretogranin 7B2-like, Ap15a-like, and ApNp35) and Deleted in Malignant Brain Tumor 1-like proteins. In summary, this study provides a new insight into the novel traits of COTS, a major pest on coral reefs, and a proteomics resource that can be used to develop (bio)control strategies and understand molecular mechanisms of regeneration.
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Vöcking O, Macias-Muñoz A, Jaeger SJ, Oakley TH. Deep Diversity: Extensive Variation in the Components of Complex Visual Systems across Animals. Cells 2022; 11:cells11243966. [PMID: 36552730 PMCID: PMC9776813 DOI: 10.3390/cells11243966] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 11/19/2022] [Accepted: 12/02/2022] [Indexed: 12/13/2022] Open
Abstract
Understanding the molecular underpinnings of the evolution of complex (multi-part) systems is a fundamental topic in biology. One unanswered question is to what the extent do similar or different genes and regulatory interactions underlie similar complex systems across species? Animal eyes and phototransduction (light detection) are outstanding systems to investigate this question because some of the genetics underlying these traits are well characterized in model organisms. However, comparative studies using non-model organisms are also necessary to understand the diversity and evolution of these traits. Here, we compare the characteristics of photoreceptor cells, opsins, and phototransduction cascades in diverse taxa, with a particular focus on cnidarians. In contrast to the common theme of deep homology, whereby similar traits develop mainly using homologous genes, comparisons of visual systems, especially in non-model organisms, are beginning to highlight a "deep diversity" of underlying components, illustrating how variation can underlie similar complex systems across taxa. Although using candidate genes from model organisms across diversity was a good starting point to understand the evolution of complex systems, unbiased genome-wide comparisons and subsequent functional validation will be necessary to uncover unique genes that comprise the complex systems of non-model groups to better understand biodiversity and its evolution.
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Affiliation(s)
- Oliver Vöcking
- Department of Biology, University of Kentucky, Lexington, KY 40508, USA
| | - Aide Macias-Muñoz
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA
| | - Stuart J. Jaeger
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA
| | - Todd H. Oakley
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA
- Correspondence:
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5
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Gühmann M, Porter ML, Bok MJ. The Gluopsins: Opsins without the Retinal Binding Lysine. Cells 2022; 11:cells11152441. [PMID: 35954284 PMCID: PMC9368030 DOI: 10.3390/cells11152441] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 07/23/2022] [Accepted: 07/28/2022] [Indexed: 12/14/2022] Open
Abstract
Opsins allow us to see. They are G-protein-coupled receptors and bind as ligand retinal, which is bound covalently to a lysine in the seventh transmembrane domain. This makes opsins light-sensitive. The lysine is so conserved that it is used to define a sequence as an opsin and thus phylogenetic opsin reconstructions discard any sequence without it. However, recently, opsins were found that function not only as photoreceptors but also as chemoreceptors. For chemoreception, the lysine is not needed. Therefore, we wondered: Do opsins exists that have lost this lysine during evolution? To find such opsins, we built an automatic pipeline for reconstructing a large-scale opsin phylogeny. The pipeline compiles and aligns sequences from public sources, reconstructs the phylogeny, prunes rogue sequences, and visualizes the resulting tree. Our final opsin phylogeny is the largest to date with 4956 opsins. Among them is a clade of 33 opsins that have the lysine replaced by glutamic acid. Thus, we call them gluopsins. The gluopsins are mainly dragonfly and butterfly opsins, closely related to the RGR-opsins and the retinochromes. Like those, they have a derived NPxxY motif. However, what their particular function is, remains to be seen.
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Affiliation(s)
- Martin Gühmann
- School of Biological Sciences, University of Bristol, Bristol BS8 1TQ, UK
- Correspondence:
| | - Megan L. Porter
- Department of Biology, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA
| | - Michael J. Bok
- Lund Vision Group, Department of Biology, University of Lund, 223 62 Lund, Sweden
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Paramonov AS, Shulepko MA, Makhonin AM, Bychkov ML, Kulbatskii DS, Chernikov AM, Myshkin MY, Shabelnikov SV, Shenkarev ZO, Kirpichnikov MP, Lyukmanova EN. New Three-Finger Protein from Starfish Asteria rubens Shares Structure and Pharmacology with Human Brain Neuromodulator Lynx2. Mar Drugs 2022; 20:md20080503. [PMID: 36005506 PMCID: PMC9410279 DOI: 10.3390/md20080503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Revised: 07/27/2022] [Accepted: 07/29/2022] [Indexed: 11/16/2022] Open
Abstract
Three-finger proteins (TFPs) are small proteins with characteristic three-finger β-structural fold stabilized by the system of conserved disulfide bonds. These proteins have been found in organisms from different taxonomic groups and perform various important regulatory functions or act as components of snake venoms. Recently, four TFPs (Lystars 1–4) with unknown function were identified in the coelomic fluid proteome of starfish A. rubens. Here we analyzed the genomes of A. rubens and A. planci starfishes and predicted additional five and six proteins containing three-finger domains, respectively. One of them, named Lystar5, is expressed in A. rubens coelomocytes and has sequence homology to the human brain neuromodulator Lynx2. The three-finger structure of Lystar5 close to the structure of Lynx2 was confirmed by NMR. Similar to Lynx2, Lystar5 negatively modulated α4β2 nicotinic acetylcholine receptors (nAChRs) expressed in X. laevis oocytes. Incubation with Lystar5 decreased the expression of acetylcholine esterase and α4 and α7 nAChR subunits in the hippocampal neurons. In summary, for the first time we reported modulator of the cholinergic system in starfish.
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Affiliation(s)
- Alexander S. Paramonov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
| | - Mikhail A. Shulepko
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
| | - Alexey M. Makhonin
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
- AI Centre, National Research University Higher School of Economics, Myasnitskaya Str. 20, 101000 Moscow, Russia
| | - Maxim L. Bychkov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
| | - Dmitrii S. Kulbatskii
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
| | - Andrey M. Chernikov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
- Interdisciplinary Scientific and Educational School of Moscow University “Molecular Technologies of the Living Systems and Synthetic Biology”, Faculty of Biology, Lomonosov Moscow State University, Leninskie Gory, 119234 Moscow, Russia
| | - Mikhail Yu. Myshkin
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
| | - Sergey V. Shabelnikov
- Institute of Cytology, Russian Academy of Sciences, Tikhoretsky Prospect 4, 194064 St. Petersburg, Russia;
| | - Zakhar O. Shenkarev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
- Moscow Institute of Physics and Technology, State University, Institutskiy Per. 9, 141701 Moscow, Russia
| | - Mikhail P. Kirpichnikov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
- Interdisciplinary Scientific and Educational School of Moscow University “Molecular Technologies of the Living Systems and Synthetic Biology”, Faculty of Biology, Lomonosov Moscow State University, Leninskie Gory, 119234 Moscow, Russia
| | - Ekaterina N. Lyukmanova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya Str. 16/10, 119997 Moscow, Russia; (A.S.P.); (M.A.S.); (A.M.M.); (M.L.B.); (D.S.K.); (A.M.C.); (M.Y.M.); (Z.O.S.); (M.P.K.)
- Interdisciplinary Scientific and Educational School of Moscow University “Molecular Technologies of the Living Systems and Synthetic Biology”, Faculty of Biology, Lomonosov Moscow State University, Leninskie Gory, 119234 Moscow, Russia
- Moscow Institute of Physics and Technology, State University, Institutskiy Per. 9, 141701 Moscow, Russia
- Correspondence:
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Kim DH, Lee YH, Sayed AEDH, Choi IY, Lee JS. Genome-wide identification of 194 G protein-coupled receptor (GPCR) genes from the water flea Daphnia magna. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART D, GENOMICS & PROTEOMICS 2022; 42:100983. [PMID: 35367896 DOI: 10.1016/j.cbd.2022.100983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 03/22/2022] [Accepted: 03/23/2022] [Indexed: 02/07/2023]
Abstract
In crustaceans, G protein-coupled receptors (GPCRs) are the largest transmembrane receptor family and function by mediating various environmental stimuli in cells. Understanding GPCR signaling is crucial to better understanding of crustacean endocrinology. GPCRs evolved from early eukaryotes, and genome-wide identification of GPCRs in a particular taxon can provide insight into evolutionary tendencies and adaptive strategies of GPCR response to environmental stimuli. Here, we identified 194 full-length GPCR genes in the water flea Daphnia magna that can be divided into five distinct classes (A, B, C, F, and other). A strong orthologous relationship for amine, neuropeptide, and opsin receptors was found in the phylogenetic comparison of D. magna GPCRs to those of humans and two well-known insects (Drosophila melanogaster and Solenopsis invicta). Our results based on phylogenetic relationships suggest that most GPCRs subfamilies have undergone sporadic evolutionary processes for adaptation to environmental pressures. Despite the dynamics of GPCR evolution, some GPCRs are highly conserved between species. This study provides a better understanding of the evolution of GPCRs and expands our knowledge of the potential physiological mechanisms in D. magna in response to various environmental stimuli.
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Affiliation(s)
- Duck-Hyun Kim
- Department of Biological Sciences, College of Science, Sungkyunkwan University, Suwon 16419, South Korea
| | - Young Hwan Lee
- Department of Biological Sciences, College of Science, Sungkyunkwan University, Suwon 16419, South Korea
| | - Alaa El-Din H Sayed
- Department of Zoology, Faculty of Science, Assiut University, 71516 Assiut, Egypt
| | - Ik-Young Choi
- Department of Agricultural Life Industry, College of Lifelong Learning, Kangwon National University, Chuncheon 24341, South Korea.
| | - Jae-Seong Lee
- Department of Biological Sciences, College of Science, Sungkyunkwan University, Suwon 16419, South Korea.
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Abstract
This review reports recent findings on the specification and patterning of neurons that establish the larval nervous system of the sea urchin embryo. Neurons originate in three regions of the embryo. Perturbation analyses enabled construction of gene regulatory networks controlling the several neural cell types. Many of the mechanisms described reflect shared features of all metazoans and others are conserved among deuterostomes. This nervous system with a very small number of neurons supports the feeding and swimming behaviors of the larva until metamorphosis when an adult nervous system replaces that system.
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Affiliation(s)
- David R McClay
- Department of Biology, Duke University, Durham, NC, United States.
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Yaguchi J, Yaguchi S. Sea urchin larvae utilize light for regulating the pyloric opening. BMC Biol 2021; 19:64. [PMID: 33820528 PMCID: PMC8022552 DOI: 10.1186/s12915-021-00999-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 03/05/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Light is essential for various biological activities. In particular, visual information through eyes or eyespots is very important for most of animals, and thus, the functions and developmental mechanisms of visual systems have been well studied to date. In addition, light-dependent non-visual systems expressing photoreceptor Opsins have been used to study the effects of light on diverse animal behaviors. However, it remains unclear how light-dependent systems were acquired and diversified during deuterostome evolution due to an almost complete lack of knowledge on the light-response signaling pathway in Ambulacraria, one of the major groups of deuterostomes and a sister group of chordates. RESULTS Here, we show that sea urchin larvae utilize light for digestive tract activity. We found that photoirradiation of larvae induces pyloric opening even without addition of food stimuli. Micro-surgical and knockdown experiments revealed that this stimulating light is received and mediated by Go(/RGR)-Opsin (Opsin3.2 in sea urchin genomes) cells around the anterior neuroectoderm. Furthermore, we found that the anterior neuroectodermal serotoninergic neurons near Go-Opsin-expressing cells are essential for mediating light stimuli-induced nitric oxide (NO) release at the pylorus. Our results demonstrate that the light>Go-Opsin>serotonin>NO pathway functions in pyloric opening during larval stages. CONCLUSIONS The results shown here will lead us to understand how light-dependent systems of pyloric opening functioning via neurotransmitters were acquired and established during animal evolution. Based on the similarity of nervous system patterns and the gut proportions among Ambulacraria, we suggest the light>pyloric opening pathway may be conserved in the clade, although the light signaling pathway has so far not been reported in other members of the group. In light of brain-gut interactions previously found in vertebrates, we speculate that one primitive function of anterior neuroectodermal neurons (brain neurons) may have been to regulate the function of the digestive tract in the common ancestor of deuterostomes. Given that food consumption and nutrient absorption are essential for animals, the acquirement and development of brain-based sophisticated gut regulatory system might have been important for deuterostome evolution.
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Affiliation(s)
- Junko Yaguchi
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, 415-0025, Japan
| | - Shunsuke Yaguchi
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, 415-0025, Japan.
- PRESTO, JST, 4-1-8 Honcho, Kawaguchi, 332-0012, Japan.
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Extraocular Vision in a Brittle Star Is Mediated by Chromatophore Movement in Response to Ambient Light. Curr Biol 2020; 30:319-327.e4. [PMID: 31902727 DOI: 10.1016/j.cub.2019.11.042] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 09/27/2019] [Accepted: 11/13/2019] [Indexed: 01/01/2023]
Abstract
Almost all animals can sense light, but only those with spatial vision can "see." Conventionally, this was restricted to animals possessing discrete visual organs (eyes), but extraocular vision could facilitate vision without eyes. Echinoderms form the focus of extraocular vision research [1-7], and the brittle star Ophiocoma wendtii, which exhibits light-responsive color change and shelter seeking, became a key species of interest [4, 8, 9]. Both O. wendtii and an apparently light-indifferent congeneric, O. pumila, possess an extensive network of r-opsin-reactive cells, but its function remains unclear [4]. We show that, although both species are strongly light averse, O. wendtii orients to stimuli necessitating spatial vision for detection, but O. pumila does not. However, O. wendtii's response disappears when chromatophores are contracted within the skeleton. Combining immunohistochemistry, histology, and synchrotron microtomography, we reconstructed models of photoreceptors in situ and extracted estimated angular apertures for O. wendtii and O. pumila. Angular sensitivity estimates, derived from these models, support the hypothesis that chromatophores constitute a screening mechanism in O. wendtii, providing sufficient resolving power to detect the stimuli. RNA sequencing (RNA-seq) identified opsin candidates in both species, including multiple r-opsins and transduction pathway constituents, congruent with immunohistochemistry and studies of other echinoderms [10, 11]. Finally, we note that differing body postures between the two species during experiments may reflect aspect of signal integration. This represents one of the most detailed mechanisms for extraocular vision yet proposed and draws interesting parallels with the only other confirmed extraocular visual system, that of some sea urchins, which also possess chromatophores [1].
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