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Racioppi C, Valoroso MC, Coppola U, Lowe EK, Brown CT, Swalla BJ, Christiaen L, Stolfi A, Ristoratore F. Evolutionary loss of melanogenesis in the tunicate Molgula occulta. EvoDevo 2017; 8:11. [PMID: 28729899 PMCID: PMC5516394 DOI: 10.1186/s13227-017-0074-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Accepted: 07/08/2017] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND Analyzing close species with diverse developmental modes is instrumental for investigating the evolutionary significance of physiological, anatomical and behavioral features at a molecular level. Many examples of trait loss are known in metazoan populations living in dark environments. Tunicates are the closest living relatives of vertebrates and typically present a lifecycle with distinct motile larval and sessile adult stages. The nervous system of the motile larva contains melanized cells associated with geotactic and light-sensing organs. It has been suggested that these are homologous to vertebrate neural crest-derived melanocytes. Probably due to ecological adaptation to distinct habitats, several species of tunicates in the Molgulidae family have tailless (anural) larvae that fail to develop sensory organ-associated melanocytes. Here we studied the evolution of Tyrosinase family genes, indispensible for melanogenesis, in the anural, unpigmented Molgula occulta and in the tailed, pigmented Molgula oculata by using phylogenetic, developmental and molecular approaches. RESULTS We performed an evolutionary reconstruction of the tunicate Tyrosinase gene family: in particular, we found that M. oculata possesses genes predicted to encode one Tyrosinase (Tyr) and three Tyrosinase-related proteins (Tyrps) while M. occulta has only Tyr and Tyrp.a pseudogenes that are not likely to encode functional proteins. Analysis of Tyr sequences from various M. occulta individuals indicates that different alleles independently acquired frameshifting short indels and/or larger mobile genetic element insertions, resulting in pseudogenization of the Tyr locus. In M. oculata, Tyr is expressed in presumptive pigment cell precursors as in the model tunicate Ciona robusta. Furthermore, a M. oculata Tyr reporter gene construct was active in the pigment cell precursors of C. robusta embryos, hinting at conservation of the regulatory network underlying Tyr expression in tunicates. In contrast, we did not observe any expression of the Tyr pseudogene in M. occulta embryos. Similarly, M. occulta Tyr allele expression was not rescued in pigmented interspecific M. occulta × M. oculata hybrid embryos, suggesting deleterious mutations also to its cis-regulatory sequences. However, in situ hybridization for transcripts from the M. occulta Tyrp.a pseudogene revealed its expression in vestigial pigment cell precursors in this species. CONCLUSIONS We reveal a complex evolutionary history of the melanogenesis pathway in tunicates, characterized by distinct gene duplication and loss events. Our expression and molecular data support a tight correlation between pseudogenization of Tyrosinase family members and the absence of pigmentation in the immotile larvae of M. occulta. These results suggest that relaxation of purifying selection has resulted in the loss of sensory organ-associated melanocytes and core genes in the melanogenesis biosynthetic pathway in M. occulta.
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Affiliation(s)
- Claudia Racioppi
- Biology and Evolution of Marine organisms, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Naples, Italy
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY USA
- Station Biologique de Roscoff, Roscoff, France
| | - Maria Carmen Valoroso
- Biology and Evolution of Marine organisms, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Naples, Italy
- Department of Biology, University of Naples Federico II, Naples, Italy
| | - Ugo Coppola
- Biology and Evolution of Marine organisms, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Naples, Italy
| | - Elijah K. Lowe
- Biology and Evolution of Marine organisms, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Naples, Italy
- Station Biologique de Roscoff, Roscoff, France
- Department of Biology, University of Washington, Seattle, WA USA
- Friday Harbor Laboratories, University of Washington, Friday Harbor, WA USA
| | - C. Titus Brown
- Station Biologique de Roscoff, Roscoff, France
- Friday Harbor Laboratories, University of Washington, Friday Harbor, WA USA
- Population Health and Reproduction, UC Davis School of Veterinary Medicine, Davis, CA USA
| | - Billie J. Swalla
- Station Biologique de Roscoff, Roscoff, France
- Department of Biology, University of Washington, Seattle, WA USA
- Friday Harbor Laboratories, University of Washington, Friday Harbor, WA USA
| | - Lionel Christiaen
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY USA
- Station Biologique de Roscoff, Roscoff, France
| | - Alberto Stolfi
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY USA
- Station Biologique de Roscoff, Roscoff, France
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA USA
| | - Filomena Ristoratore
- Biology and Evolution of Marine organisms, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Naples, Italy
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Esposito R, Racioppi C, Pezzotti MR, Branno M, Locascio A, Ristoratore F, Spagnuolo A. The ascidian pigmented sensory organs: structures and developmental programs. Genesis 2014; 53:15-33. [PMID: 25382437 DOI: 10.1002/dvg.22836] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 11/03/2014] [Accepted: 11/04/2014] [Indexed: 01/25/2023]
Abstract
The recent advances on ascidian pigment sensory organ development and function represent a fascinating platform to get insight on the basic programs of chordate eye formation. This review aims to summarize current knowledge, at the structural and molecular levels, on the two main building blocks of ascidian light sensory organ, i.e. pigment cells and photoreceptor cells. The unique features of these structures (e.g., simplicity and well characterized cell lineage) are indeed making it possible to dissect the developmental programs at single cell resolution and will soon provide a panel of molecular tools to be exploited for a deep developmental and comparative-evolutionary analysis.
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Affiliation(s)
- R Esposito
- Cellular and Developmental Biology Department, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121, NAPOLI, Italy
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Abstract
Recent findings shed light on the steps underlying the evolution of vertebrate photoreceptors and retina. Vertebrate ciliary photoreceptors are not as wholly distinct from invertebrate rhabdomeric photoreceptors as is sometimes thought. Recent information on the phylogenies of ciliary and rhabdomeric opsins has helped in constructing the likely routes followed during evolution. Clues to the factors that led the early vertebrate retina to become invaginated can be obtained by combining recent knowledge about the origin of the pathway for dark re-isomerization of retinoids with knowledge of the inability of ciliary opsins to undergo photoreversal, along with consideration of the constraints imposed under the very low light levels in the deep ocean. Investigation of the origin of cell classes in the vertebrate retina provides support for the notion that cones, rods and bipolar cells all originated from a primordial ciliary photoreceptor, whereas ganglion cells, amacrine cells and horizontal cells all originated from rhabdomeric photoreceptors. Knowledge of the molecular differences between cones and rods, together with knowledge of the scotopic signalling pathway, provides an understanding of the evolution of rods and of the rods' retinal circuitry. Accordingly, it has been possible to propose a plausible scenario for the sequence of evolutionary steps that led to the emergence of vertebrate photoreceptors and retina.
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Affiliation(s)
- Trevor D Lamb
- ARC Centre of Excellence in Vision Science, The Australian National University, Canberra ACT 0200, Australia.
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Sordino P, Andreakis N, Brown ER, Leccia NI, Squarzoni P, Tarallo R, Alfano C, Caputi L, D'Ambrosio P, Daniele P, D'Aniello E, D'Aniello S, Maiella S, Miraglia V, Russo MT, Sorrenti G, Branno M, Cariello L, Cirino P, Locascio A, Spagnuolo A, Zanetti L, Ristoratore F. Natural variation of model mutant phenotypes in Ciona intestinalis. PLoS One 2008; 3:e2344. [PMID: 18523552 PMCID: PMC2391289 DOI: 10.1371/journal.pone.0002344] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2007] [Accepted: 04/17/2008] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND The study of ascidians (Chordata, Tunicata) has made a considerable contribution to our understanding of the origin and evolution of basal chordates. To provide further information to support forward genetics in Ciona intestinalis, we used a combination of natural variation and neutral population genetics as an approach for the systematic identification of new mutations. In addition to the significance of developmental variation for phenotype-driven studies, this approach can encompass important implications in evolutionary and population biology. METHODOLOGY/PRINCIPAL FINDINGS Here, we report a preliminary survey for naturally occurring mutations in three geographically interconnected populations of C. intestinalis. The influence of historical, geographical and environmental factors on the distribution of abnormal phenotypes was assessed by means of 12 microsatellites. We identified 37 possible mutant loci with stereotyped defects in embryonic development that segregate in a way typical of recessive alleles. Local populations were found to differ in genetic organization and frequency distribution of phenotypic classes. CONCLUSIONS/SIGNIFICANCE Natural genetic polymorphism of C. intestinalis constitutes a valuable source of phenotypes for studying embryonic development in ascidians. Correlating genetic structure and the occurrence of abnormal phenotypes is a crucial focus for understanding the selective forces that shape natural finite populations, and may provide insights of great importance into the evolutionary mechanisms that generate animal diversity.
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Affiliation(s)
- Paolo Sordino
- Laboratory of Biochemistry and Molecular Biology, Stazione Zoologica Anton Dohrn, Naples, Italy.
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Jeffery WR. Chordate ancestry of the neural crest: New insights from ascidians. Semin Cell Dev Biol 2007; 18:481-91. [PMID: 17509911 DOI: 10.1016/j.semcdb.2007.04.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2007] [Revised: 01/31/2007] [Accepted: 04/10/2007] [Indexed: 11/29/2022]
Abstract
This article reviews new insights from ascidians on the ancestry of vertebrate neural crest (NC) cells. Ascidians have neural crest-like cells (NCLC), which migrate from the dorsal midline, express some of the typical NC markers, and develop into body pigment cells. These characters suggest that primordial NC cells were already present in the common ancestor of the vertebrates and urochordates, which have been recently inferred as sister groups. The primitive role of NCLC may have been in pigment cell dispersal and development. Later, additional functions may have appeared in the vertebrate lineage, resulting in the evolution of definitive NC cells.
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Affiliation(s)
- William R Jeffery
- Department of Biology, University of Maryland, College Park, MD 20742, USA.
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Jeffery WR. Ascidian neural crest-like cells: phylogenetic distribution, relationship to larval complexity, and pigment cell fate. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2006; 306:470-80. [PMID: 16619245 DOI: 10.1002/jez.b.21109] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Migratory neural crest-like cells, which express the cell surface antigen HNK-1 and develop into pigment cells, have recently been identified in the ascidian Ecteinascidia turbinata. Here we use HNK-1 expression as a marker to determine whether neural crest-like cells are responsible for pigment development in diverse ascidian species. We surveyed HNK-1 expression and tyrosinase activity in 12 ascidian species, including those with different adult organizations, developmental modes, and larval sizes and complexities. We observed HNK-1 positive cells in every species, although the timing of HNK-1 expression varied according to the extent of larval complexity. HNK-1 expression was initiated during the late tailbud stage in species in which adult features are formed precociously in large complex larvae. In contrast, HNK-1 positive cells did not appear until the swimming tadpole or juvenile stage in species with small simple larvae in which most adult features appear after metamorphosis. Double labeling experiments indicated that HNK-1 and tyrosinase are expressed in the same subset of pigment-forming mesenchymal cells in species with complex or simple larvae. In addition, the absence of HNK-1 and tyrosinase expression in albino morphs of the colonial ascidian Botryllus schlosseri suggested that the major fate of neural crest-like cells is to become pigment cells. The results suggest that ascidian neural crest-like cells and vertebrate neural crest cells had a common origin during chordate evolution and that their primitive function was to generate body pigmentation.
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Affiliation(s)
- William R Jeffery
- Department of Biology, University of Maryland, College Park, Maryland 20742, USA.
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