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Bedois AMH, Parker HJ, Price AJ, Morrison JA, Bronner ME, Krumlauf R. Sea lamprey enlightens the origin of the coupling of retinoic acid signaling to vertebrate hindbrain segmentation. Nat Commun 2024; 15:1538. [PMID: 38378737 PMCID: PMC10879103 DOI: 10.1038/s41467-024-45911-x] [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: 07/05/2023] [Accepted: 02/06/2024] [Indexed: 02/22/2024] Open
Abstract
Retinoic acid (RA) is involved in antero-posterior patterning of the chordate body axis and, in jawed vertebrates, has been shown to play a major role at multiple levels of the gene regulatory network (GRN) regulating hindbrain segmentation. Knowing when and how RA became coupled to the core hindbrain GRN is important for understanding how ancient signaling pathways and patterning genes can evolve and generate diversity. Hence, we investigated the link between RA signaling and hindbrain segmentation in the sea lamprey Petromyzon marinus, an important jawless vertebrate model providing clues to decipher ancestral vertebrate features. Combining genomics, gene expression, and functional analyses of major components involved in RA synthesis (Aldh1as) and degradation (Cyp26s), we demonstrate that RA signaling is coupled to hindbrain segmentation in lamprey. Thus, the link between RA signaling and hindbrain segmentation is a pan vertebrate feature of the hindbrain and likely evolved at the base of vertebrates.
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Affiliation(s)
- Alice M H Bedois
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Hugo J Parker
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Andrew J Price
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Jason A Morrison
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA.
- Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, MO, 66160, USA.
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2
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Andrade López JM, Pani AM, Wu M, Gerhart J, Lowe CJ. Molecular characterization of nervous system organization in the hemichordate acorn worm Saccoglossus kowalevskii. PLoS Biol 2023; 21:e3002242. [PMID: 37725784 PMCID: PMC10508912 DOI: 10.1371/journal.pbio.3002242] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 07/11/2023] [Indexed: 09/21/2023] Open
Abstract
Hemichordates are an important group for investigating the evolution of bilaterian nervous systems. As the closest chordate outgroup with a bilaterally symmetric adult body plan, hemichordates are particularly informative for exploring the origins of chordates. Despite the importance of hemichordate neuroanatomy for testing hypotheses on deuterostome and chordate evolution, adult hemichordate nervous systems have not been comprehensively described using molecular techniques, and classic histological descriptions disagree on basic aspects of nervous system organization. A molecular description of hemichordate nervous system organization is important for both anatomical comparisons across phyla and for attempts to understand how conserved gene regulatory programs for ectodermal patterning relate to morphological evolution in deep time. Here, we describe the basic organization of the adult hemichordate Saccoglossus kowalevskii nervous system using immunofluorescence, in situ hybridization, and transgenic reporters to visualize neurons, neuropil, and key neuronal cell types. Consistent with previous descriptions, we found the S. kowalevskii nervous system consists of a pervasive nerve plexus concentrated in the anterior, along with nerve cords on both the dorsal and ventral side. Neuronal cell types exhibited clear anteroposterior and dorsoventral regionalization in multiple areas of the body. We observed spatially demarcated expression patterns for many genes involved in synthesis or transport of neurotransmitters and neuropeptides but did not observe clear distinctions between putatively centralized and decentralized portions of the nervous system. The plexus shows regionalized structure and is consistent with the proboscis base as a major site for information processing rather than the dorsal nerve cord. In the trunk, there is a clear division of cell types between the dorsal and ventral cords, suggesting differences in function. The absence of neural processes crossing the basement membrane into muscle and extensive axonal varicosities suggest that volume transmission may play an important role in neural function. These data now facilitate more informed neural comparisons between hemichordates and other groups, contributing to broader debates on the origins and evolution of bilaterian nervous systems.
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Affiliation(s)
- José M. Andrade López
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Ariel M. Pani
- Departments of Biology and Cell Biology, University of Virginia, Charlottesville, Virginia, Unites States of America
| | - Mike Wu
- Department of Molecular and Cell Biology, University of California, Berkeley, California, Unites States of America
| | - John Gerhart
- Department of Molecular and Cell Biology, University of California, Berkeley, California, Unites States of America
| | - Christopher J. Lowe
- Department of Biology, Stanford University, Stanford, California, United States of America
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3
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Bedois AMH, Parker HJ, Bronner ME, Krumlauf R. Sea lamprey enlightens the origin of the coupling of retinoic acid signaling to vertebrate hindbrain segmentation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.07.548143. [PMID: 37461675 PMCID: PMC10350081 DOI: 10.1101/2023.07.07.548143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Retinoic acid (RA) is involved in antero-posterior patterning of the chordate body axis and, in jawed vertebrates, has been shown to play a major role at multiple levels of the gene regulatory network (GRN) regulating hindbrain segmentation. Knowing when and how RA became coupled to the core hindbrain GRN is important for understanding how ancient signaling pathways and patterning genes can evolve and generate diversity. Hence, we investigated the link between RA signaling and hindbrain segmentation in the sea lamprey Petromyzon marinus, an important jawless vertebrate model providing clues to decipher ancestral vertebrate features. Combining genomics, gene expression, and functional analyses of major components involved in RA synthesis (Aldh1as) and degradation (Cyp26s), we demonstrate that RA signaling is coupled to hindbrain segmentation in lamprey. Thus, the link between RA signaling and hindbrain segmentation is a pan vertebrate feature of the hindbrain and likely evolved at the base of vertebrates.
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Affiliation(s)
- Alice M. H. Bedois
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
| | - Hugo J. Parker
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
| | - Marianne E. Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
- Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, Kansas 66160, USA
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4
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Howard AGA, Uribe RA. Hox proteins as regulators of extracellular matrix interactions during neural crest migration. Differentiation 2022; 128:26-32. [PMID: 36228422 PMCID: PMC10802151 DOI: 10.1016/j.diff.2022.09.003] [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: 08/02/2022] [Revised: 09/23/2022] [Accepted: 09/25/2022] [Indexed: 01/19/2023]
Abstract
Emerging during embryogenesis, the neural crest are a migratory, transient population of multipotent stem cell that differentiates into various cell types in vertebrates. Neural crest cells arise along the anterior-posterior extent of the neural tube, delaminate and migrate along routes to their final destinations. The factors that orchestrate how neural crest cells undergo delamination and their subsequent sustained migration is not fully understood. This review provides a primer about neural crest epithelial-to-mesenchymal transition (EMT), with a special emphasis on the role of the Extracellular matrix (ECM), cellular effector proteins of EMT, and subsequent migration. We also summarize published findings that link the expression of Hox transcription factors to EMT and ECM modification, thereby implicating Hox factors in regulation of EMT and ECM remodeling during neural crest cell ontogenesis.
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Affiliation(s)
- Aubrey G A Howard
- BioSciences Department, Rice University, Houston, TX, 77005, USA; Biochemistry and Cell Biology Program, Rice University, Houston, TX, 77005, USA
| | - Rosa A Uribe
- BioSciences Department, Rice University, Houston, TX, 77005, USA; Biochemistry and Cell Biology Program, Rice University, Houston, TX, 77005, USA.
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5
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Martí-Clua J. Times of neuron origin and neurogenetic gradients in mice Purkinje cells and deep cerebellar nuclei neurons during the development of the cerebellum. A review. Tissue Cell 2022; 78:101897. [DOI: 10.1016/j.tice.2022.101897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2022] [Revised: 08/09/2022] [Accepted: 08/12/2022] [Indexed: 11/16/2022]
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6
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Du Z, Zhang D, Li J, Li Q, Pang Y. Lamprey immune protein triggers the ferroptosis pathway during zebrafish embryonic development. Cell Commun Signal 2022; 20:124. [PMID: 35978430 PMCID: PMC9386916 DOI: 10.1186/s12964-022-00933-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Accepted: 07/08/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Previously, a novel lamprey immune protein (LIP) was identified, which plays an important role in immunity and the regulation of growth and development in lampreys. However, the mechanism of how LIP regulates growth and development remains unclear. METHODS In this study, a zebrafish model of LIP overexpression was established by delivering a transgenic plasmid to the fertilized egg. The biological function of LIP was explored in vivo through phenotypic characterization, comparative transcriptome sequencing, and physiological and biochemical analyses. RESULTS LIP caused developmental toxicity in zebrafish, increased embryo mortality and exhibited strong teratogenic, lethal, and developmental inhibitory effects. Comparative transcriptome analysis showed that LIP-induced large-scale cell death by triggering ferroptosis. Furthermore, LIP-induced lipid peroxidation and caused pericardial edema. Direct inhibition of acsl4a and tfr1a, or silencing of acsl4a and tfr1a with specific siRNA suppressed ferroptosis and pericardial edema. CONCLUSIONS Taken together, we confirmed that LIP can participate in growth and development via the regulation of lipid peroxidation and ferroptosis. This lays the foundation for future studies on the function of LIP in lampreys. Video Abstract.
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Affiliation(s)
- Zeyu Du
- College of Life Science, Liaoning Normal University, Dalian, 116081, China.,Lamprey Research Center, Liaoning Normal University, Dalian, 116081, China.,Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116023, China
| | - Duo Zhang
- College of Life Science, Liaoning Normal University, Dalian, 116081, China.,Lamprey Research Center, Liaoning Normal University, Dalian, 116081, China.,Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116023, China
| | - Jun Li
- College of Life Science, Liaoning Normal University, Dalian, 116081, China.,Lamprey Research Center, Liaoning Normal University, Dalian, 116081, China.,Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116023, China
| | - Qingwei Li
- College of Life Science, Liaoning Normal University, Dalian, 116081, China.,Lamprey Research Center, Liaoning Normal University, Dalian, 116081, China.,Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116023, China
| | - Yue Pang
- College of Life Science, Liaoning Normal University, Dalian, 116081, China. .,Lamprey Research Center, Liaoning Normal University, Dalian, 116081, China. .,Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116023, China.
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7
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Genome-wide analysis of cis-regulatory changes underlying metabolic adaptation of cavefish. Nat Genet 2022; 54:684-693. [PMID: 35551306 DOI: 10.1038/s41588-022-01049-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Accepted: 03/09/2022] [Indexed: 12/13/2022]
Abstract
Cis-regulatory changes are key drivers of adaptative evolution. However, their contribution to the metabolic adaptation of organisms is not well understood. Here, we used a unique vertebrate model, Astyanax mexicanus-different morphotypes of which survive in nutrient-rich surface and nutrient-deprived cave waters-to uncover gene regulatory networks underlying metabolic adaptation. We performed genome-wide epigenetic profiling in the liver tissues of Astyanax and found that many of the identified cis-regulatory elements (CREs) have genetically diverged and have differential chromatin features between surface and cave morphotypes, while retaining remarkably similar regulatory signatures between independently derived cave populations. One such CRE in the hpdb gene harbors a genomic deletion in cavefish that abolishes IRF2 repressor binding and derepresses enhancer activity in reporter assays. Selection of this mutation in multiple independent cave populations supports its importance in cave adaptation, and provides novel molecular insights into the evolutionary trade-off between loss of pigmentation and adaptation to food-deprived caves.
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8
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Papadogiannis V, Pennati A, Parker HJ, Rothbächer U, Patthey C, Bronner ME, Shimeld SM. Hmx gene conservation identifies the origin of vertebrate cranial ganglia. Nature 2022; 605:701-705. [PMID: 35585239 DOI: 10.1038/s41586-022-04742-w] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Accepted: 04/07/2022] [Indexed: 12/30/2022]
Abstract
The evolutionary origin of vertebrates included innovations in sensory processing associated with the acquisition of a predatory lifestyle1. Vertebrates perceive external stimuli through sensory systems serviced by cranial sensory ganglia, whose neurons arise predominantly from cranial placodes; however, the understanding of the evolutionary origin of placodes and cranial sensory ganglia is hampered by the anatomical differences between living lineages and the difficulty in assigning homology between cell types and structures. Here we show that the homeobox transcription factor Hmx is a constitutive component of vertebrate sensory ganglion development and that in the tunicate Ciona intestinalis, Hmx is necessary and sufficient to drive the differentiation programme of bipolar tail neurons, cells previously thought to be homologues of neural crest2,3. Using Ciona and lamprey transgenesis, we demonstrate that a unique, tandemly duplicated enhancer pair regulated Hmx expression in the stem-vertebrate lineage. We also show notably robust vertebrate Hmx enhancer function in Ciona, demonstrating that deep conservation of the upstream regulatory network spans the evolutionary origin of vertebrates. These experiments demonstrate regulatory and functional conservation between Ciona and vertebrate Hmx, and point to bipolar tail neurons as homologues of cranial sensory ganglia.
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Affiliation(s)
- Vasileios Papadogiannis
- Department of Zoology, University of Oxford, Oxford, UK.,Institute of Marine Biology, Biotechnology and Aquaculture, Hellenic Centre for Marine Research, Gournes, Crete, Greece
| | - Alessandro Pennati
- Department of Zoology, University of Oxford, Oxford, UK.,Institute of Zoology and Center of Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Hugo J Parker
- Stowers Institute for Medical Research, Kansas City, MO, USA
| | - Ute Rothbächer
- Institute of Zoology and Center of Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Cedric Patthey
- Department of Radiation Sciences, Oncology, Umeå University, Umeå, Sweden
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
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9
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Parker HJ, De Kumar B, Pushel I, Bronner ME, Krumlauf R. Analysis of lamprey meis genes reveals that conserved inputs from Hox, Meis and Pbx proteins control their expression in the hindbrain and neural tube. Dev Biol 2021; 479:61-76. [PMID: 34310923 DOI: 10.1016/j.ydbio.2021.07.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 06/10/2021] [Accepted: 07/22/2021] [Indexed: 11/23/2022]
Abstract
Meis genes are known to play important roles in the hindbrain and neural crest cells of jawed vertebrates. To explore the roles of Meis genes in head development during evolution of vertebrates, we have identified four meis genes in the sea lamprey genome and characterized their patterns of expression and regulation, with a focus on the hindbrain and pharynx. Each of the lamprey meis genes displays temporally and spatially dynamic patterns of expression, some of which are coupled to rhombomeric domains in the developing hindbrain and select pharyngeal arches. Studies of Meis loci in mouse and zebrafish have identified enhancers that are bound by Hox and TALE (Meis and Pbx) proteins, implicating these factors in the direct regulation of Meis expression. We examined the lamprey meis loci and identified a series of cis-elements conserved between lamprey and jawed vertebrate meis genes. In transgenic reporter assays we demonstrated that these elements act as neural enhancers in lamprey embryos, directing reporter expression in appropriate domains when compared to expression of their associated endogenous meis gene. Sequence alignments reveal that these conserved elements are in similar relative positions of the meis loci and contain a series of consensus binding motifs for Hox and TALE proteins. This suggests that ancient Hox and TALE-responsive enhancers regulated expression of ancestral vertebrate meis genes in segmental domains in the hindbrain and have been retained in the meis loci during vertebrate evolution. The presence of conserved Meis, Pbx and Hox binding sites in these lamprey enhancers links Hox and TALE factors to regulation of lamprey meis genes in the developing hindbrain, indicating a deep ancestry for these regulatory interactions prior to the divergence of jawed and jawless vertebrates.
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Affiliation(s)
- Hugo J Parker
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Bony De Kumar
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Irina Pushel
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, MO, 64110, USA; Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, KS, 66160, USA.
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10
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Abstract
During early development, the hindbrain is sub-divided into rhombomeres that underlie the organisation of neurons and adjacent craniofacial tissues. A gene regulatory network of signals and transcription factors establish and pattern segments with a distinct anteroposterior identity. Initially, the borders of segmental gene expression are imprecise, but then become sharply defined, and specialised boundary cells form. In this Review, we summarise key aspects of the conserved regulatory cascade that underlies the formation of hindbrain segments. We describe how the pattern is sharpened and stabilised through the dynamic regulation of cell identity, acting in parallel with cell segregation. Finally, we discuss evidence that boundary cells have roles in local patterning, and act as a site of neurogenesis within the hindbrain.
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Affiliation(s)
- Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA.,Dept of Anatomy and Cell Biology, Kansas University Medical School, Kansas City, KS 66160, USA
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11
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Fuiten AM, Cresko WA. Evolutionary divergence of a Hoxa2b hindbrain enhancer in syngnathids mimics results of functional assays. Dev Genes Evol 2021; 231:57-71. [PMID: 34003345 DOI: 10.1007/s00427-021-00676-x] [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: 12/28/2020] [Accepted: 04/29/2021] [Indexed: 10/21/2022]
Abstract
Hoxa2 genes provide critical patterning signals during development, and their regulation and function have been extensively studied. We report a previously uncharacterized significant sequence divergence of a highly conserved hindbrain hoxa2b enhancer element in the family syngnathidae (pipefishes, seahorses, pipehorses, seadragons). We compared the hox cis-regulatory element variation in the Gulf pipefish and two species of seahorse against eight other species of fish, as well as human and mouse. We annotated the hoxa2b enhancer element binding sites across three species of seahorse, four species of pipefish, and one species of ghost pipefish. Finally, we performed in situ hybridization analysis of hoxa2b expression in Gulf pipefish embryos. We found that all syngnathid fish examined share a modified rhombomere 4 hoxa2b enhancer element, despite the fact that this element has been found to be highly conserved across all vertebrates examined previously. Binding element sequence motifs and spacing between binding elements have been modified for the hoxa2b enhancer in several species of pipefish and seahorse, and that the loss of the Prep/Meis binding site and further space shortening happened after ghost pipefish split from the rest of the syngnathid clade. We showed that expression of this gene in rhombomere 4 is lower relative to the surrounding rhombomeres in developing Gulf pipefish embryos, reflecting previously published functional tests for this enhancer. Our findings highlight the benefits of studying highly derived, diverse taxa for understanding of gene regulatory evolution and support the hypothesis that natural mutations can occur in deeply conserved pathways in ways potentially related to phenotypic diversity.
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Affiliation(s)
- Allison M Fuiten
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA
- Present address: Department of Dermatology, Oregon Health and Science University, Portland, OR, 97239, USA
| | - William A Cresko
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403, USA.
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12
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Abstract
Vertebrates develop an olfactory system that detects odorants and pheromones through their interaction with specialized cell surface receptors on olfactory sensory neurons. During development, the olfactory system forms from the olfactory placodes, specialized areas of the anterior ectoderm that share cellular and molecular properties with placodes involved in the development of other cranial senses. The early-diverging chordate lineages amphioxus, tunicates, lampreys and hagfishes give insight into how this system evolved. Here, we review olfactory system development and cell types in these lineages alongside chemosensory receptor gene evolution, integrating these data into a description of how the vertebrate olfactory system evolved. Some olfactory system cell types predate the vertebrates, as do some of the mechanisms specifying placodes, and it is likely these two were already connected in the common ancestor of vertebrates and tunicates. In stem vertebrates, this evolved into an organ system integrating additional tissues and morphogenetic processes defining distinct olfactory and adenohypophyseal components, followed by splitting of the ancestral placode to produce the characteristic paired olfactory organs of most modern vertebrates.
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Affiliation(s)
- Guillaume Poncelet
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Sebastian M Shimeld
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
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13
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Kusakabe R, Higuchi S, Tanaka M, Kadota M, Nishimura O, Kuratani S. Novel developmental bases for the evolution of hypobranchial muscles in vertebrates. BMC Biol 2020; 18:120. [PMID: 32907560 PMCID: PMC7488077 DOI: 10.1186/s12915-020-00851-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Accepted: 08/18/2020] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND Vertebrates are characterized by possession of hypobranchial muscles (HBMs). Cyclostomes, or modern jawless vertebrates, possess a rudimentary and superficial HBM lateral to the pharynx, whereas the HBM in jawed vertebrates is internalized and anteroposteriorly specified. Precursor cells of the HBM, marked by expression of Lbx1, originate from somites and undergo extensive migration before becoming innervated by the hypoglossal nerve. How the complex form of HBM arose in evolution is relevant to the establishment of the vertebrate body plan, but despite having long been assumed to be similar to that of limb muscles, modification of developmental mechanisms of HBM remains enigmatic. RESULTS Here we characterize the expression of Lbx genes in lamprey and hagfish (cyclostomes) and catshark (gnathostome; jawed vertebrates). We show that the expression patterns of the single cyclostome Lbx homologue, Lbx-A, do not resemble the somitic expression of mammalian Lbx1. Disruption of Lbx-A revealed that LjLbx-A is required for the formation of both HBM and body wall muscles, likely due to the insufficient extension of precursor cells rather than to hindered muscle differentiation. Both homologues of Lbx in the catshark were expressed in the somitic muscle primordia, unlike in amniotes. During catshark embryogenesis, Lbx2 is expressed in the caudal HBM as well as in the abdominal rectus muscle, similar to lamprey Lbx-A, whereas Lbx1 marks the rostral HBM and pectoral fin muscle. CONCLUSIONS We conclude that the vertebrate HBM primarily emerged as a specialized somatic muscle to cover the pharynx, and the anterior internalized HBM of the gnathostomes is likely a novelty added rostral to the cyclostome-like HBM, for which duplication and functionalization of Lbx genes would have been a prerequisite.
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Affiliation(s)
- Rie Kusakabe
- Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), 2-2-3 Minatojima-minami, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.
| | - Shinnosuke Higuchi
- Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), 2-2-3 Minatojima-minami, Chuo-ku, Kobe, Hyogo, 650-0047, Japan
- Department of Biology, Graduate School of Science, Kobe University, Kobe, 657-8501, Japan
- Department of Molecular Biology and Biochemistry, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, 734-8553, Japan
| | - Masako Tanaka
- Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), 2-2-3 Minatojima-minami, Chuo-ku, Kobe, Hyogo, 650-0047, Japan
| | - Mitsutaka Kadota
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, 650-0047, Japan
| | - Osamu Nishimura
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, 650-0047, Japan
| | - Shigeru Kuratani
- Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), 2-2-3 Minatojima-minami, Chuo-ku, Kobe, Hyogo, 650-0047, Japan
- Evolutionary Morphology Laboratory, RIKEN Cluster for Pioneering Research (CPR), Kobe, 650-0047, Japan
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14
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An evolutionarily ancient mechanism for regulation of hemoglobin expression in vertebrate red cells. Blood 2020; 136:269-278. [PMID: 32396940 DOI: 10.1182/blood.2020004826] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 04/23/2020] [Indexed: 11/20/2022] Open
Abstract
The oxygen transport function of hemoglobin (HB) is thought to have arisen ∼500 million years ago, roughly coinciding with the divergence between jawless (Agnatha) and jawed (Gnathostomata) vertebrates. Intriguingly, extant HBs of jawless and jawed vertebrates were shown to have evolved twice, and independently, from different ancestral globin proteins. This raises the question of whether erythroid-specific expression of HB also evolved twice independently. In all jawed vertebrates studied to date, one of the HB gene clusters is linked to the widely expressed NPRL3 gene. Here we show that the nprl3-linked hb locus of a jawless vertebrate, the river lamprey (Lampetra fluviatilis), shares a range of structural and functional properties with the equivalent jawed vertebrate HB locus. Functional analysis demonstrates that an erythroid-specific enhancer is located in intron 7 of lamprey nprl3, which corresponds to the NPRL3 intron 7 MCS-R1 enhancer of jawed vertebrates. Collectively, our findings signify the presence of an nprl3-linked multiglobin gene locus, which contains a remote enhancer that drives globin expression in erythroid cells, before the divergence of jawless and jawed vertebrates. Different globin genes from this ancestral cluster evolved in the current NPRL3-linked HB genes in jawless and jawed vertebrates. This provides an explanation of the enigma of how, in different species, globin genes linked to the same adjacent gene could undergo convergent evolution.
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15
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Peter IS. The function of architecture and logic in developmental gene regulatory networks. Curr Top Dev Biol 2020; 139:267-295. [PMID: 32450963 DOI: 10.1016/bs.ctdb.2020.04.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
An important contribution of systems biology is the insight that biological systems depend on the function of molecular interactions and not just on individual molecules. System level mechanisms are particularly important in the development of animals and plants which depends not just on transcription factors and signaling molecules, but also on regulatory circuits and gene regulatory networks (GRNs). However, since GRNs consist of transcription factors, it can be challenging to assess the function of regulatory circuits independently of the function of regulatory factors. The comparison of different GRNs offers a way to do so and leads to several observations. First, similar regulatory circuits operate in various developmental contexts and in different species, and frequently, these circuits are associated with similar developmental functions. Second, given regulatory circuits are often used at particular positions within the GRN hierarchy. Third, in some GRNs, regulatory circuits are organized in a particular order in respect to each other. And fourth, the evolution of GRNs occurs not just by co-option of regulatory genes but also by rewiring of regulatory linkages between conserved regulatory genes, indicating that the organization of interactions is important. Thus, even though in most instances the function of regulatory circuits remains to be discovered, it becomes evident that the architecture and logic of GRNs are functionally important for the control of genome activity and for the specification of the body plan.
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Affiliation(s)
- Isabelle S Peter
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States.
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16
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Onimaru K. The evolutionary origin of developmental enhancers in vertebrates: Insights from non‐model species. Dev Growth Differ 2020; 62:326-333. [DOI: 10.1111/dgd.12662] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 03/10/2020] [Accepted: 03/11/2020] [Indexed: 11/28/2022]
Affiliation(s)
- Koh Onimaru
- Laboratory for Bioinformatics Research RIKEN Center for Biosystems Dynamics Research (BDR) Wako CitySaitama Japan
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17
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York JR, McCauley DW. Functional genetic analysis in a jawless vertebrate, the sea lamprey: insights into the developmental evolution of early vertebrates. J Exp Biol 2020; 223:223/Suppl_1/jeb206433. [DOI: 10.1242/jeb.206433] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
ABSTRACT
Lampreys and hagfishes are the only surviving relicts of an ancient but ecologically dominant group of jawless fishes that evolved in the seas of the Cambrian era over half a billion years ago. Because of their phylogenetic position as the sister group to all other vertebrates (jawed vertebrates), comparisons of embryonic development between jawless and jawed vertebrates offers researchers in the field of evolutionary developmental biology the unique opportunity to address fundamental questions related to the nature of our earliest vertebrate ancestors. Here, we describe how genetic analysis of embryogenesis in the sea lamprey (Petromyzon marinus) has provided insight into the origin and evolution of developmental-genetic programs in vertebrates. We focus on recent work involving CRISPR/Cas9-mediated genome editing to study gene regulatory mechanisms involved in the development and evolution of neural crest cells and new cell types in the vertebrate nervous system, and transient transgenic assays that have been instrumental in dissecting the evolution of cis-regulatory control of gene expression in vertebrates. Finally, we discuss the broad potential for these functional genomic tools to address previously unanswerable questions related to the evolution of genomic regulatory mechanisms as well as issues related to invasive sea lamprey population control.
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Affiliation(s)
- Joshua R. York
- Department of Biology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA
| | - David W. McCauley
- Department of Biology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA
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18
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Parker HJ, Krumlauf R. A Hox gene regulatory network for hindbrain segmentation. Curr Top Dev Biol 2020; 139:169-203. [DOI: 10.1016/bs.ctdb.2020.03.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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19
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Hockman D, Chong-Morrison V, Green SA, Gavriouchkina D, Candido-Ferreira I, Ling ITC, Williams RM, Amemiya CT, Smith JJ, Bronner ME, Sauka-Spengler T. A genome-wide assessment of the ancestral neural crest gene regulatory network. Nat Commun 2019; 10:4689. [PMID: 31619682 PMCID: PMC6795873 DOI: 10.1038/s41467-019-12687-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Accepted: 09/23/2019] [Indexed: 12/17/2022] Open
Abstract
The neural crest (NC) is an embryonic cell population that contributes to key vertebrate-specific features including the craniofacial skeleton and peripheral nervous system. Here we examine the transcriptional and epigenomic profiles of NC cells in the sea lamprey, in order to gain insight into the ancestral state of the NC gene regulatory network (GRN). Transcriptome analyses identify clusters of co-regulated genes during NC specification and migration that show high conservation across vertebrates but also identify transcription factors (TFs) and cell-adhesion molecules not previously implicated in NC migration. ATAC-seq analysis uncovers an ensemble of cis-regulatory elements, including enhancers of Tfap2B, SoxE1 and Hox-α2 validated in the embryo. Cross-species deployment of lamprey elements identifies the deep conservation of lamprey SoxE1 enhancer activity, mediating homologous expression in jawed vertebrates. Our data provide insight into the core GRN elements conserved to the base of the vertebrates and expose others that are unique to lampreys.
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Affiliation(s)
- Dorit Hockman
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
- Division of Cell Biology, Department of Human Biology, Neuroscience Institute, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Vanessa Chong-Morrison
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
- Division of Biosciences, Faculty of Life Sciences, University College London, London, UK
| | - Stephen A Green
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Daria Gavriouchkina
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
- Okinawa Institute of Science and Technology, Molecular Genetics Unit, Onna, Japan
| | - Ivan Candido-Ferreira
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Irving T C Ling
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Ruth M Williams
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Chris T Amemiya
- Molecular Cell Biology, School of Natural Sciences, University of California, Merced, CA, USA
| | - Jeramiah J Smith
- Department of Biology, University of Kentucky, Lexington, KY, USA
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Tatjana Sauka-Spengler
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK.
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20
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Martik ML, Gandhi S, Uy BR, Gillis JA, Green SA, Simoes-Costa M, Bronner ME. Evolution of the new head by gradual acquisition of neural crest regulatory circuits. Nature 2019; 574:675-678. [PMID: 31645763 PMCID: PMC6858584 DOI: 10.1038/s41586-019-1691-4] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Accepted: 09/26/2019] [Indexed: 12/02/2022]
Abstract
The neural crest, an embryonic stem-cell population, is a vertebrate innovation that has been proposed to be a key component of the 'new head', which imbued vertebrates with predatory behaviour1,2. Here, to investigate how the evolution of neural crest cells affected the vertebrate body plan, we examined the molecular circuits that control neural crest development along the anteroposterior axis of a jawless vertebrate, the sea lamprey. Gene expression analysis showed that the cranial subpopulation of the neural crest of the lamprey lacks most components of a transcriptional circuit that is specific to the cranial neural crest in amniotes and confers the ability to form craniofacial cartilage onto non-cranial neural crest subpopulations3. Consistent with this, hierarchical clustering analysis revealed that the transcriptional profile of the lamprey cranial neural crest is more similar to the trunk neural crest of amniotes. Notably, analysis of the cranial neural crest in little skate and zebrafish embryos demonstrated that the transcriptional circuit that is specific to the cranial neural crest emerged via the gradual addition of network components to the neural crest of gnathostomes, which subsequently became restricted to the cephalic region. Our results indicate that the ancestral neural crest at the base of the vertebrate lineage possessed a trunk-like identity. We propose that the emergence of the cranial neural crest, by progressive assembly of an axial-specific regulatory circuit, allowed the elaboration of the new head during vertebrate evolution.
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Affiliation(s)
- Megan L Martik
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Shashank Gandhi
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Benjamin R Uy
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - J Andrew Gillis
- Department of Zoology, University of Cambridge, Cambridge, UK
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, USA
| | - Stephen A Green
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Marcos Simoes-Costa
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.
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21
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Prummel KD, Hess C, Nieuwenhuize S, Parker HJ, Rogers KW, Kozmikova I, Racioppi C, Brombacher EC, Czarkwiani A, Knapp D, Burger S, Chiavacci E, Shah G, Burger A, Huisken J, Yun MH, Christiaen L, Kozmik Z, Müller P, Bronner M, Krumlauf R, Mosimann C. A conserved regulatory program initiates lateral plate mesoderm emergence across chordates. Nat Commun 2019; 10:3857. [PMID: 31451684 PMCID: PMC6710290 DOI: 10.1038/s41467-019-11561-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 07/22/2019] [Indexed: 01/06/2023] Open
Abstract
Cardiovascular lineages develop together with kidney, smooth muscle, and limb connective tissue progenitors from the lateral plate mesoderm (LPM). How the LPM initially emerges and how its downstream fates are molecularly interconnected remain unknown. Here, we isolate a pan-LPM enhancer in the zebrafish-specific draculin (drl) gene that provides specific LPM reporter activity from early gastrulation. In toto live imaging and lineage tracing of drl-based reporters captures the dynamic LPM emergence as lineage-restricted mesendoderm field. The drl pan-LPM enhancer responds to the transcription factors EomesoderminA, FoxH1, and MixL1 that combined with Smad activity drive LPM emergence. We uncover specific activity of zebrafish-derived drl reporters in LPM-corresponding territories of several chordates including chicken, axolotl, lamprey, Ciona, and amphioxus, revealing a universal upstream LPM program. Altogether, our work provides a mechanistic framework for LPM emergence as defined progenitor field, possibly representing an ancient mesodermal cell state that predates the primordial vertebrate embryo. Numerous tissues are derived from the lateral plate mesoderm (LPM) but how this is specified is unclear. Here, the authors identify a pan-LPM reporter activity found in the zebrafish draculin (drl) gene that also shows transgenic activity in LPM-corresponding territories of several chordates, including chicken, axolotl, lamprey, Ciona, and amphioxus.
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Affiliation(s)
- Karin D Prummel
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Christopher Hess
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Susan Nieuwenhuize
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Hugo J Parker
- Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, KS, 66160, USA.,Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Katherine W Rogers
- Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, 72076, Germany
| | - Iryna Kozmikova
- Institute of Molecular Genetics of the ASCR, Prague, 142 20, Czech Republic
| | - Claudia Racioppi
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY, 10003, USA
| | - Eline C Brombacher
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Anna Czarkwiani
- TUD-CRTD Center for Regenerative Therapies Dresden, Dresden, 01307, Germany
| | - Dunja Knapp
- TUD-CRTD Center for Regenerative Therapies Dresden, Dresden, 01307, Germany
| | - Sibylle Burger
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Elena Chiavacci
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Gopi Shah
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, 01307, Germany
| | - Alexa Burger
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland
| | - Jan Huisken
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, 01307, Germany.,Morgridge Institute for Research, Madison, WI, 53715, USA
| | - Maximina H Yun
- TUD-CRTD Center for Regenerative Therapies Dresden, Dresden, 01307, Germany.,Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, 01307, Germany
| | - Lionel Christiaen
- Center for Developmental Genetics, Department of Biology, New York University, New York, NY, 10003, USA
| | - Zbynek Kozmik
- Institute of Molecular Genetics of the ASCR, Prague, 142 20, Czech Republic
| | - Patrick Müller
- Friedrich Miescher Laboratory of the Max Planck Society, Tübingen, 72076, Germany
| | - Marianne Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Robb Krumlauf
- Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, KS, 66160, USA.,Stowers Institute for Medical Research, Kansas City, MO, 64110, USA
| | - Christian Mosimann
- Institute of Molecular Life Sciences, University of Zurich, Zürich, 8057, Switzerland.
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22
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Cambronero F, Ariza‐McNaughton L, Wiedemann LM, Krumlauf R. Inter‐rhombomeric interactions reveal roles for fibroblast growth factors signaling in segmental regulation of
EphA4
expression. Dev Dyn 2019; 249:354-368. [DOI: 10.1002/dvdy.101] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 08/08/2019] [Accepted: 08/09/2019] [Indexed: 12/15/2022] Open
Affiliation(s)
| | | | - Leanne M. Wiedemann
- Stowers Institute for Medical Research Kansas City Missouri
- Department of Pathology and Laboratory MedicineKansas University Medical Center Kansas City Kansas
| | - Robb Krumlauf
- Stowers Institute for Medical Research Kansas City Missouri
- Division of Developmental NeurobiologyNational Institute for Medical Research London UK
- Department of Anatomy and Cell BiologyKansas University Medical School Kansas City Kansas
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23
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Leung B, Shimeld SM. Evolution of vertebrate spinal cord patterning. Dev Dyn 2019; 248:1028-1043. [PMID: 31291046 DOI: 10.1002/dvdy.77] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 06/14/2019] [Accepted: 06/15/2019] [Indexed: 12/17/2022] Open
Abstract
The vertebrate spinal cord is organized across three developmental axes, anterior-posterior (AP), dorsal-ventral (DV), and medial-lateral (ML). Patterning of these axes is regulated by canonical intercellular signaling pathways: the AP axis by Wnt, fibroblast growth factor, and retinoic acid (RA), the DV axis by Hedgehog, Tgfβ, and Wnt, and the ML axis where proliferation is controlled by Notch. Developmental time plays an important role in which signal does what and when. Patterning across the three axes is not independent, but linked by interactions between signaling pathway components and their transcriptional targets. Combined this builds a sophisticated organ with many different types of cell in specific AP, DV, and ML positions. Two living lineages share phylum Chordata with vertebrates, amphioxus, and tunicates, while the jawless fish such as lampreys, survive as the most basally divergent vertebrate lineage. Genes and mechanisms shared between lampreys and other vertebrates tell us what predated vertebrates, while those also shared with other chordates tell us what evolved early in chordate evolution. Between these lie vertebrate innovations: genetic and developmental changes linked to evolution of new morphology. These include gene duplications, differences in how signals are received, and new regulatory connections between signaling pathways and their target genes.
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Affiliation(s)
- Brigid Leung
- Department of Zoology, University of Oxford, Oxford, UK
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24
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Onimaru K, Kuraku S. Inference of the ancestral vertebrate phenotype through vestiges of the whole-genome duplications. Brief Funct Genomics 2019; 17:352-361. [PMID: 29566222 PMCID: PMC6158797 DOI: 10.1093/bfgp/ely008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Inferring the phenotype of the last common ancestor of living vertebrates is a challenging problem because of several unresolvable factors. They include the lack of reliable out-groups of living vertebrates, poor information about less fossilizable organs and specialized traits of phylogenetically important species, such as lampreys and hagfishes (e.g. secondary loss of vertebrae in adult hagfishes). These factors undermine the reliability of ancestral reconstruction by traditional character mapping approaches based on maximum parsimony. In this article, we formulate an approach to hypothesizing ancestral vertebrate phenotypes using information from the phylogenetic and functional properties of genes duplicated by genome expansions in early vertebrate evolution. We named the conjecture as ‘chronological reconstruction of ohnolog functions (CHROF)’. This CHROF conjecture raises the possibility that the last common ancestor of living vertebrates may have had more complex traits than currently thought.
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Affiliation(s)
- Koh Onimaru
- RIKEN Center for Life Science Technologies, Kobe, Hyogo Japan.,Department of biological science, Tokyo Institute of Technology, Tokyo, Japan
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25
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Parker HJ, Bronner ME, Krumlauf R. An atlas of anterior hox gene expression in the embryonic sea lamprey head: Hox-code evolution in vertebrates. Dev Biol 2019; 453:19-33. [PMID: 31071313 DOI: 10.1016/j.ydbio.2019.05.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Revised: 04/05/2019] [Accepted: 05/01/2019] [Indexed: 10/26/2022]
Abstract
In the hindbrain and the adjacent cranial neural crest (NC) cells of jawed vertebrates (gnathostomes), nested and segmentally-restricted domains of Hox gene expression provide a combinatorial Hox-code for specifying regional properties during head development. Extant jawless vertebrates, such as the sea lamprey (Petromyzon marinus), can provide insights into the evolution and diversification of this Hox-code in vertebrates. There is evidence for gnathostome-like spatial patterns of Hox expression in lamprey; however, the expression domains of the majority of lamprey hox genes from paralogy groups (PG) 1-4 are yet to be characterized, so it is unknown whether they are coupled to hindbrain segments (rhombomeres) and NC. In this study, we systematically describe the spatiotemporal expression of all 14 sea lamprey hox genes from PG1-PG4 in the developing hindbrain and pharynx to investigate the extent to which their expression conforms to the archetypal gnathostome hindbrain and pharyngeal hox-codes. We find many similarities in Hox expression between lamprey and gnathostome species, particularly in rhombomeric domains during hindbrain segmentation and in the cranial neural crest, enabling inference of aspects of Hox expression in the ancestral vertebrate embryonic head. These data are consistent with the idea that a Hox regulatory network underlying hindbrain segmentation is a pan vertebrate trait. We also reveal differences in hindbrain domains at later stages, as well as expression in the endostyle and in pharyngeal arch (PA) 1 mesoderm. Our analysis suggests that many Hox expression domains that are observed in extant gnathostomes were present in ancestral vertebrates but have been partitioned differently across Hox clusters in gnathostome and cyclostome lineages after duplication.
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Affiliation(s)
- Hugo J Parker
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, KS 66160, USA.
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26
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A Hox-TALE regulatory circuit for neural crest patterning is conserved across vertebrates. Nat Commun 2019; 10:1189. [PMID: 30867425 PMCID: PMC6416258 DOI: 10.1038/s41467-019-09197-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 02/26/2019] [Indexed: 12/13/2022] Open
Abstract
In jawed vertebrates (gnathostomes), Hox genes play an important role in patterning head and jaw formation, but mechanisms coupling Hox genes to neural crest (NC) are unknown. Here we use cross-species regulatory comparisons between gnathostomes and lamprey, a jawless extant vertebrate, to investigate conserved ancestral mechanisms regulating Hox2 genes in NC. Gnathostome Hoxa2 and Hoxb2 NC enhancers mediate equivalent NC expression in lamprey and gnathostomes, revealing ancient conservation of Hox upstream regulatory components in NC. In characterizing a lamprey hoxα2 NC/hindbrain enhancer, we identify essential Meis, Pbx, and Hox binding sites that are functionally conserved within Hoxa2/Hoxb2 NC enhancers. This suggests that the lamprey hoxα2 enhancer retains ancestral activity and that Hoxa2/Hoxb2 NC enhancers are ancient paralogues, which diverged in hindbrain and NC activities. This identifies an ancestral mechanism for Hox2 NC regulation involving a Hox-TALE regulatory circuit, potentiated by inputs from Meis and Pbx proteins and Hox auto-/cross-regulatory interactions.
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27
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Minor PJ, Clarke DN, Andrade López JM, Fritzenwanker JH, Gray J, Lowe CJ. I-SceI Meganuclease-mediated transgenesis in the acorn worm, Saccoglossus kowalevskii. Dev Biol 2019; 445:8-15. [PMID: 30412702 PMCID: PMC6327965 DOI: 10.1016/j.ydbio.2018.10.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 10/29/2018] [Accepted: 10/29/2018] [Indexed: 11/17/2022]
Abstract
Hemichordates are a phylum of marine invertebrate deuterostomes that are closely related to chordates, and represent one of the most promising models to provide insights into early deuterostome evolution. The genome of the hemichordate, Saccoglossus kowalevskii, reveals an extensive set of non-coding elements conserved across all three deuterostome phyla. Functional characterization and cross-phyla comparisons of these putative regulatory elements will enable a better understanding of enhancer evolution, and subsequently how changes in gene regulation give rise to morphological innovation. Here, we describe an efficient method of transgenesis for the characterization of non-coding elements in S. kowalevskii. We first test the capacity of an I-SceI transgenesis system to drive ubiquitous or regionalized gene expression, and to label specific cell types. Finally, we identified a minimal promoter that can be used to test the capacity of putative enhancers in S. kowalevskii. This work demonstrates that this I-SceI transgenesis technique, when coupled with an understanding of chromatin accessibility, can be a powerful tool for studying how evolutionary changes in gene regulatory mechanisms contributed to the diversification of body plans in deuterostomes.
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Affiliation(s)
- Paul J Minor
- Hopkins Marine Station, Department of Biology, Stanford University, 120 Oceanview Blvd., Pacific Grove, CA 93950, United States.
| | - D Nathaniel Clarke
- Hopkins Marine Station, Department of Biology, Stanford University, 120 Oceanview Blvd., Pacific Grove, CA 93950, United States
| | - José M Andrade López
- Hopkins Marine Station, Department of Biology, Stanford University, 120 Oceanview Blvd., Pacific Grove, CA 93950, United States
| | - Jens H Fritzenwanker
- Department of Biology, Georgetown University, 411 Regents Hall, 37th and O Streets, NW, Washington DC 20057, United States
| | - Jessica Gray
- Department of Systems Biology, Harvard Medical School, 200 Longwood Ave, Boston, MA 02115, United States
| | - Christopher J Lowe
- Hopkins Marine Station, Department of Biology, Stanford University, 120 Oceanview Blvd., Pacific Grove, CA 93950, United States.
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28
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Abstract
AbstractAlthough the color violet is now used in a wide variety of everyday products, ranging from toys to clothing to cars, and although it now appears commonly in artistic works, violet was rarely used in fine art before the early 1860s. The color violet only became an integral part of modern culture and life with the rise of the French Impressionists. I investigated the use of violet in over 130,000 artworks prior to 1863 and found that it appeared in about .06 percent of the paintings. Violet was used substantially more frequently in Impressionist works, and remains popular in fine art and in popular culture today. I examine several explanations for the explosion of the use of violet in the art world during the Impressionist era, and conclude that a cognitive-perceptual explanation, based on the heightened sensitivity of the Impressionists to short wavelengths, may account for it. The findings fit with a new understanding about evolutionary changes in planetary light and human adaptation to light.
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29
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Wood TWP, Nakamura T. Problems in Fish-to-Tetrapod Transition: Genetic Expeditions Into Old Specimens. Front Cell Dev Biol 2018; 6:70. [PMID: 30062096 PMCID: PMC6054942 DOI: 10.3389/fcell.2018.00070] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 06/15/2018] [Indexed: 12/30/2022] Open
Abstract
The fish-to-tetrapod transition is one of the fundamental problems in evolutionary biology. A significant amount of paleontological data has revealed the morphological trajectories of skeletons, such as those of the skull, vertebrae, and appendages in vertebrate history. Shifts in bone differentiation, from dermal to endochondral bones, are key to explaining skeletal transformations during the transition from water to land. However, the genetic underpinnings underlying the evolution of dermal and endochondral bones are largely missing. Recent genetic approaches utilizing model organisms—zebrafish, frogs, chickens, and mice—reveal the molecular mechanisms underlying vertebrate skeletal development and provide new insights for how the skeletal system has evolved. Currently, our experimental horizons to test evolutionary hypotheses are being expanded to non-model organisms with state-of-the-art techniques in molecular biology and imaging. An integration of functional genomics, developmental genetics, and high-resolution CT scanning into evolutionary inquiries allows us to reevaluate our understanding of old specimens. Here, we summarize the current perspectives in genetic programs underlying the development and evolution of the dermal skull roof, shoulder girdle, and appendages. The ratio shifts of dermal and endochondral bones, and its underlying mechanisms, during the fish-to-tetrapod transition are particularly emphasized. Recent studies have suggested the novel cell origins of dermal bones, and the interchangeability between dermal and endochondral bones, obscuring the ontogenetic distinction of these two types of bones. Assimilation of ontogenetic knowledge of dermal and endochondral bones from different structures demands revisions of the prevalent consensus in the evolutionary mechanisms of vertebrate skeletal shifts.
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Affiliation(s)
- Thomas W P Wood
- Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ, United States
| | - Tetsuya Nakamura
- Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ, United States
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30
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Dynamic regulation of Nanog and stem cell-signaling pathways by Hoxa1 during early neuro-ectodermal differentiation of ES cells. Proc Natl Acad Sci U S A 2018; 114:5838-5845. [PMID: 28584089 DOI: 10.1073/pnas.1610612114] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Homeobox a1 (Hoxa1) is one of the most rapidly induced genes in ES cell differentiation and it is the earliest expressed Hox gene in the mouse embryo. In this study, we used genomic approaches to identify Hoxa1-bound regions during early stages of ES cell differentiation into the neuro-ectoderm. Within 2 h of retinoic acid treatment, Hoxa1 is rapidly recruited to target sites that are associated with genes involved in regulation of pluripotency, and these genes display early changes in expression. The pattern of occupancy of Hoxa1 is dynamic and changes over time. At 12 h of differentiation, many sites bound at 2 h are lost and a new cohort of bound regions appears. At both time points the genome-wide mapping reveals that there is significant co-occupancy of Nanog (Nanog homeobox) and Hoxa1 on many common target sites, and these are linked to genes in the pluripotential regulatory network. In addition to shared target genes, Hoxa1 binds to regulatory regions of Nanog, and conversely Nanog binds to a 3' enhancer of Hoxa1 This finding provides evidence for direct cross-regulatory feedback between Hoxa1 and Nanog through a mechanism of mutual repression. Hoxa1 also binds to regulatory regions of Sox2 (sex-determining region Y box 2), Esrrb (estrogen-related receptor beta), and Myc, which underscores its key input into core components of the pluripotential regulatory network. We propose a model whereby direct inputs of Nanog and Hoxa1 on shared targets and mutual repression between Hoxa1 and the core pluripotency network provides a molecular mechanism that modulates the fine balance between the alternate states of pluripotency and differentiation.
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31
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Pascual-Anaya J, Sato I, Sugahara F, Higuchi S, Paps J, Ren Y, Takagi W, Ruiz-Villalba A, Ota KG, Wang W, Kuratani S. Hagfish and lamprey Hox genes reveal conservation of temporal colinearity in vertebrates. Nat Ecol Evol 2018; 2:859-866. [PMID: 29610468 DOI: 10.1038/s41559-018-0526-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Accepted: 03/01/2018] [Indexed: 11/09/2022]
Abstract
Hox genes exert fundamental roles for proper regional specification along the main rostro-caudal axis of animal embryos. They are generally expressed in restricted spatial domains according to their position in the cluster (spatial colinearity)-a feature that is conserved across bilaterians. In jawed vertebrates (gnathostomes), the position in the cluster also determines the onset of expression of Hox genes (a feature known as whole-cluster temporal colinearity (WTC)), while in invertebrates this phenomenon is displayed as a subcluster-level temporal colinearity. However, little is known about the expression profile of Hox genes in jawless vertebrates (cyclostomes); therefore, the evolutionary origin of WTC, as seen in gnathostomes, remains a mystery. Here, we show that Hox genes in cyclostomes are expressed according to WTC during development. We investigated the Hox repertoire and Hox gene expression profiles in three different species-a hagfish, a lamprey and a shark-encompassing the two major groups of vertebrates, and found that these are expressed following a whole-cluster, temporally staggered pattern, indicating that WTC has been conserved during the past 500 million years despite drastically different genome evolution and morphological outputs between jawless and jawed vertebrates.
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Affiliation(s)
| | - Iori Sato
- Evolutionary Morphology Laboratory, RIKEN, Kobe, Japan.,Evolutionary Morphology Research Team, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
| | - Fumiaki Sugahara
- Evolutionary Morphology Laboratory, RIKEN, Kobe, Japan.,Division of Biology, Hyogo College of Medicine, Nishinomiya, Japan
| | - Shinnosuke Higuchi
- Evolutionary Morphology Laboratory, RIKEN, Kobe, Japan.,Evolutionary Morphology Research Team, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
| | - Jordi Paps
- School of Biological Sciences, University of Essex, Colchester, UK
| | - Yandong Ren
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Wataru Takagi
- Evolutionary Morphology Laboratory, RIKEN, Kobe, Japan.,Physiology Laboratory, Atmosphere Ocean Research Institute, The University of Tokyo, Chiba, Japan
| | - Adrián Ruiz-Villalba
- Centro de Investigación Médica Aplicada (CIMA), Área de Terapia Celular, Universidad de Navarra, Pamplona, Spain.,Instituto de Salud Pública de Navarra, IdiSNA, Pamplona, Spain
| | - Kinya G Ota
- Laboratory of Aquatic Zoology, Marine Research Station, Institute of Cellular and Organismic Biology, Academia Sinica, Yilan, Taiwan
| | - Wen Wang
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China
| | - Shigeru Kuratani
- Evolutionary Morphology Laboratory, RIKEN, Kobe, Japan.,Evolutionary Morphology Research Team, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
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Coupling the roles of Hox genes to regulatory networks patterning cranial neural crest. Dev Biol 2018; 444 Suppl 1:S67-S78. [PMID: 29571614 DOI: 10.1016/j.ydbio.2018.03.016] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Revised: 03/17/2018] [Accepted: 03/17/2018] [Indexed: 11/20/2022]
Abstract
The neural crest is a transient population of cells that forms within the developing central nervous system and migrates away to generate a wide range of derivatives throughout the body during vertebrate embryogenesis. These cells are of evolutionary and clinical interest, constituting a key defining trait in the evolution of vertebrates and alterations in their development are implicated in a high proportion of birth defects and craniofacial abnormalities. In the hindbrain and the adjacent cranial neural crest cells (cNCCs), nested domains of Hox gene expression provide a combinatorial'Hox-code' for specifying regional properties in the developing head. Hox genes have been shown to play important roles at multiple stages in cNCC development, including specification, migration, and differentiation. However, relatively little is known about the underlying gene-regulatory mechanisms involved, both upstream and downstream of Hox genes. Furthermore, it is still an open question as to how the genes of the neural crest GRN are linked to Hox-dependent pathways. In this review, we describe Hox gene expression, function and regulation in cNCCs with a view to integrating these genes within the emerging gene regulatory network for cNCC development. We highlight early roles for Hox1 genes in cNCC specification, proposing that this may be achieved, in part, by regulation of the balance between pluripotency and differentiation in precursor cells within the neuro-epithelium. We then describe what is known about the regulation of Hox gene expression in cNCCs and discuss this from the perspective of early vertebrate evolution.
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33
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The neural crest and evolution of the head/trunk interface in vertebrates. Dev Biol 2018; 444 Suppl 1:S60-S66. [PMID: 29408469 DOI: 10.1016/j.ydbio.2018.01.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2017] [Revised: 01/24/2018] [Accepted: 01/24/2018] [Indexed: 12/31/2022]
Abstract
The migration and distribution patterns of neural crest (NC) cells reflect the distinct embryonic environments of the head and trunk: cephalic NC cells migrate predominantly along the dorsolateral pathway to populate the craniofacial and pharyngeal regions, whereas trunk crest cells migrate along the ventrolateral pathways to form the dorsal root ganglia. These two patterns thus reflect the branchiomeric and somitomeric architecture, respectively, of the vertebrate body plan. The so-called vagal NC occupies a postotic, intermediate level between the head and trunk NC. This level of NC gives rise to both trunk- and cephalic-type (circumpharyngeal) NC cells. The anatomical pattern of the amphioxus, a basal chordate, suggests that somites and pharyngeal gills coexist along an extensive length of the body axis, indicating that the embryonic environment is similar to that of vertebrate vagal NC cells and may have been ancestral for vertebrates. The amniote-like condition in which the cephalic and trunk domains are distinctly separated would have been brought about, in part, by anteroposterior reduction of the pharyngeal domain.
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Buchanan JT. Swimming rhythm generation in the caudal hindbrain of the lamprey. J Neurophysiol 2018; 119:1681-1692. [PMID: 29364070 DOI: 10.1152/jn.00851.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The spinal cord has been well established as the site of generation of the locomotor rhythm in vertebrates, but studies have suggested that the caudal hindbrain in larval fish and amphibians can also generate locomotor rhythms. Here, we investigated whether the caudal hindbrain of the adult lamprey ( Petromyzon marinus and Ichthyomyzon unicuspis) has the ability to generate the swimming rhythm. The hindbrain-spinal cord transition zone of the lamprey contains a bilateral column of somatic motoneurons that project via the spino-occipital (S-O) nerves to several muscles of the head. In the brainstem-spinal cord-muscle preparation, these muscles were found to burst and contract rhythmically with a left-right alternation when swimming activity was evoked with a brief electrical stimulation of the spinal cord. In the absence of muscles, the isolated brainstem-spinal cord preparation also produced alternating left-right bursts in S-O nerves (i.e., fictive swimming), and the S-O nerve bursts preceded the bursts occurring in the first ipsilateral spinal ventral root. After physical isolation of the S-O region using transverse cuts of the nervous system, the S-O nerves still exhibited rhythmic bursting with left-right alternation when glutamate was added to the bathing solution. We conclude that the S-O region of the lamprey contains a swimming rhythm generator that produces the leading motor nerve bursts of each swimming cycle, which then propagate down the spinal cord to produce forward swimming. The S-O region of the hindbrain-spinal cord transition zone may play a role in regulating speed, turning, and head orientation during swimming in lamprey. NEW & NOTEWORTHY Although it has been well established that locomotor rhythm generation occurs in the spinal cord of vertebrates, it was unknown whether the hindbrain of the adult vertebrate nervous system can also generate the locomotor rhythm. Here, we show that the isolated hindbrain-spinal cord transition zone of adult lamprey can generate the swimming rhythm. In addition, the swimming bursts of the hindbrain lead the bursts occurring in the first segment of the spinal cord.
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Affiliation(s)
- James T Buchanan
- Department of Biological Sciences, Marquette University , Milwaukee, Wisconsin
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35
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The sea lamprey germline genome provides insights into programmed genome rearrangement and vertebrate evolution. Nat Genet 2018; 50:270-277. [PMID: 29358652 PMCID: PMC5805609 DOI: 10.1038/s41588-017-0036-1] [Citation(s) in RCA: 183] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 12/15/2017] [Indexed: 12/24/2022]
Abstract
The sea lamprey (Petromyzon marinus) serves as a comparative model for reconstructing vertebrate evolution. To enable more informed analyses, we developed a new assembly of the lamprey germline genome that integrates several complementary datasets. Analysis of this highly contiguous (chromosome-scale) assembly reveals that both chromosomal and whole-genome duplications have played significant roles in the evolution of ancestral vertebrate and lamprey genomes, including chromosomes that carry the six lamprey HOX clusters. The assembly also contains several hundred genes that are reproducibly eliminated from somatic cells during early development in lamprey. Comparative analyses show that gnathostome (mouse) homologs of these genes are frequently marked by Polycomb Repressive Complexes (PRCs) in embryonic stem cells, suggesting overlaps in the regulatory logic of somatic DNA elimination and repressive/bivalent states that are regulated by early embryonic PRCs. This new assembly will enhance diverse studies that are informed by lampreys’ unique biology and evolutionary/comparative perspective.
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36
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Hoxa1 targets signaling pathways during neural differentiation of ES cells and mouse embryogenesis. Dev Biol 2017; 432:151-164. [DOI: 10.1016/j.ydbio.2017.09.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Revised: 09/27/2017] [Accepted: 09/28/2017] [Indexed: 11/20/2022]
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37
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Roles of Retinoic Acid Signaling in Shaping the Neuronal Architecture of the Developing Amphioxus Nervous System. Mol Neurobiol 2017; 55:5210-5229. [PMID: 28875454 DOI: 10.1007/s12035-017-0727-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 08/08/2017] [Indexed: 02/01/2023]
Abstract
The morphogen retinoic acid (RA) patterns vertebrate nervous systems and drives neurogenesis, but how these functions evolved remains elusive. Here, we show that RA signaling plays stage- and tissue-specific roles during the formation of neural cell populations with serotonin, dopamine, and GABA neurotransmitter phenotypes in amphioxus, a proxy for the ancestral chordate. Our data suggest that RA signaling restricts the specification of dopamine-containing cells in the ectoderm and of GABA neurons in the neural tube, probably by regulating Hox1 and Hox3 gene expression, respectively. The two Hox genes thus appear to serve distinct functions rather than to participate in a combinatorial Hox code. We were further able to correlate the RA signaling-dependent mispatterning of hindbrain GABA neurons with concomitant motor impairments. Taken together, these data provide new insights into how RA signaling and Hox genes contribute to nervous system as well as to motor control development in amphioxus and hence shed light on the evolution of these functions within vertebrates.
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38
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Fritzsch B, Elliott KL, Glover JC. Gaskell revisited: new insights into spinal autonomics necessitate a revised motor neuron nomenclature. Cell Tissue Res 2017; 370:195-209. [PMID: 28856468 DOI: 10.1007/s00441-017-2676-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 07/21/2017] [Indexed: 01/01/2023]
Abstract
Several concepts developed in the nineteenth century have formed the basis of much of our neuroanatomical teaching today. Not all of these were based on solid evidence nor have withstood the test of time. Recent evidence on the evolution and development of the autonomic nervous system, combined with molecular insights into the development and diversification of motor neurons, challenges some of the ideas held for over 100 years about the organization of autonomic motor outflow. This review provides an overview of the original ideas and quality of supporting data and contrasts this with a more accurate and in depth insight provided by studies using modern techniques. Several lines of data demonstrate that branchial motor neurons are a distinct motor neuron population within the vertebrate brainstem, from which parasympathetic visceral motor neurons of the brainstem evolved. The lack of an autonomic nervous system in jawless vertebrates implies that spinal visceral motor neurons evolved out of spinal somatic motor neurons. Consistent with the evolutionary origin of brainstem parasympathetic motor neurons out of branchial motor neurons and spinal sympathetic motor neurons out of spinal motor neurons is the recent revision of the organization of the autonomic nervous system into a cranial parasympathetic and a spinal sympathetic division (e.g., there is no sacral parasympathetic division). We propose a new nomenclature that takes all of these new insights into account and avoids the conceptual misunderstandings and incorrect interpretation of limited and technically inferior data inherent in the old nomenclature.
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Affiliation(s)
- Bernd Fritzsch
- Department of Biology, University of Iowa, 129 E Jefferson Street, 214 Biology Building, Iowa City, IA, 52242, USA. .,Center on Aging & Aging Mind and Brain Initiative, Weslawn Office 2159 A-2, Iowa City, IA, 52242-1324, USA.
| | - Karen L Elliott
- Department of Biology, University of Iowa, 129 E Jefferson Street, 214 Biology Building, Iowa City, IA, 52242, USA
| | - Joel C Glover
- Department of Molecular Medicine, University of Oslo, Oslo, Norway.,Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
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39
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Parker HJ, Krumlauf R. Segmental arithmetic: summing up the Hox gene regulatory network for hindbrain development in chordates. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2017; 6. [PMID: 28771970 DOI: 10.1002/wdev.286] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2017] [Revised: 06/13/2017] [Accepted: 06/15/2017] [Indexed: 11/10/2022]
Abstract
Organization and development of the early vertebrate hindbrain are controlled by a cascade of regulatory interactions that govern the process of segmentation and patterning along the anterior-posterior axis via Hox genes. These interactions can be assembled into a gene regulatory network that provides a framework to interpret experimental data, generate hypotheses, and identify gaps in our understanding of the progressive process of hindbrain segmentation. The network can be broadly separated into a series of interconnected programs that govern early signaling, segmental subdivision, secondary signaling, segmentation, and ultimately specification of segmental identity. Hox genes play crucial roles in multiple programs within this network. Furthermore, the network reveals properties and principles that are likely to be general to other complex developmental systems. Data from vertebrate and invertebrate chordate models are shedding light on the origin and diversification of the network. Comprehensive cis-regulatory analyses of vertebrate Hox gene regulation have enabled powerful cross-species gene regulatory comparisons. Such an approach in the sea lamprey has revealed that the network mediating segmental Hox expression was present in ancestral vertebrates and has been maintained across diverse vertebrate lineages. Invertebrate chordates lack hindbrain segmentation but exhibit conservation of some aspects of the network, such as a role for retinoic acid in establishing nested Hox expression domains. These comparisons lead to a model in which early vertebrates underwent an elaboration of the network between anterior-posterior patterning and Hox gene expression, leading to the gene-regulatory programs for segmental subdivision and rhombomeric segmentation. WIREs Dev Biol 2017, 6:e286. doi: 10.1002/wdev.286 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Hugo J Parker
- Stowers Institute for Medical Research, Kansas City, MO, USA
| | - Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, MO, USA.,Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, Kansas 66160, USA
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40
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Neijts R, Deschamps J. At the base of colinear Hox gene expression: cis -features and trans -factors orchestrating the initial phase of Hox cluster activation. Dev Biol 2017; 428:293-299. [DOI: 10.1016/j.ydbio.2017.02.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 02/16/2017] [Indexed: 10/19/2022]
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41
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CTCF binding landscape in jawless fish with reference to Hox cluster evolution. Sci Rep 2017; 7:4957. [PMID: 28694486 PMCID: PMC5504073 DOI: 10.1038/s41598-017-04506-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 05/17/2017] [Indexed: 11/25/2022] Open
Abstract
The nuclear protein CCCTC-binding factor (CTCF) contributes as an insulator to chromatin organization in animal genomes. Currently, our knowledge of its binding property is confined mainly to mammals. In this study, we identified CTCF homologs in extant jawless fishes and performed ChIP-seq for the CTCF protein in the Arctic lamprey. Our phylogenetic analysis suggests that the lamprey lineage experienced gene duplication that gave rise to its unique paralog, designated CTCF2, which is independent from the previously recognized duplication between CTCF and CTCFL. The ChIP-seq analysis detected comparable numbers of CTCF binding sites between lamprey, chicken, and human, and revealed that the lamprey CTCF protein binds to the two-part motif, consisting of core and upstream motifs previously reported for mammals. These findings suggest that this mode of CTCF binding was established in the last common ancestor of extant vertebrates (more than 500 million years ago). We analyzed CTCF binding inside Hox clusters, which revealed a reinforcement of CTCF binding in the region spanning Hox1-4 genes that is unique to lamprey. Our study provides not only biological insights into the antiquity of CTCF-based epigenomic regulation known in mammals but also a technical basis for comparative epigenomic studies encompassing the whole taxon Vertebrata.
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42
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Square T, Jandzik D, Romášek M, Cerny R, Medeiros DM. The origin and diversification of the developmental mechanisms that pattern the vertebrate head skeleton. Dev Biol 2017; 427:219-229. [DOI: 10.1016/j.ydbio.2016.11.014] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 10/06/2016] [Accepted: 11/20/2016] [Indexed: 01/30/2023]
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Abstract
Hox gene collinearity was discovered be Edward B. Lewis in 1978. It consists of the Hox1, Hox2, Hox3 ordering of the Hox genes in the chromosome from the telomeric to the centromeric side of the chromosome. Surprisingly, the spatial activation of the Hox genes in the ontogenetic units of the embryo follows the same ordering along the anterior-posterior embryonic axis. The chromosome microscale differs from the embryo macroscale by 3 to 4 orders of magnitude. The traditional biomolecular mechanisms are not adequate to comprise phenomena at so divergent spatial domains. A Biophysical Model of physical forces was proposed which can bridge the intermediate space and explain the results of genetic engineering experiments. Recent progress in constructing instruments and achieving high resolution imaging (e.g., 3D DNA FISH, STORM etc.) enable the assessment of the geometric structure of the chromatin during the different phases of Hox gene activation. It is found that the mouse HoxD gene cluster is elongated up to 5-6 times during Hox gene transcription. These unexpected findings agree with the BM predictions. It is now possible to measure several physical quantities inside the nucleus during Hox gene activation. New experiments are proposed to test further this model.
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Tschopp P, Tabin CJ. Deep homology in the age of next-generation sequencing. Philos Trans R Soc Lond B Biol Sci 2017; 372:20150475. [PMID: 27994118 PMCID: PMC5182409 DOI: 10.1098/rstb.2015.0475] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/08/2016] [Indexed: 12/14/2022] Open
Abstract
The principle of homology is central to conceptualizing the comparative aspects of morphological evolution. The distinctions between homologous or non-homologous structures have become blurred, however, as modern evolutionary developmental biology (evo-devo) has shown that novel features often result from modification of pre-existing developmental modules, rather than arising completely de novo. With this realization in mind, the term 'deep homology' was coined, in recognition of the remarkably conserved gene expression during the development of certain animal structures that would not be considered homologous by previous strict definitions. At its core, it can help to formulate an understanding of deeper layers of ontogenetic conservation for anatomical features that lack any clear phylogenetic continuity. Here, we review deep homology and related concepts in the context of a gene expression-based homology discussion. We then focus on how these conceptual frameworks have profited from the recent rise of high-throughput next-generation sequencing. These techniques have greatly expanded the range of organisms amenable to such studies. Moreover, they helped to elevate the traditional gene-by-gene comparison to a transcriptome-wide level. We will end with an outlook on the next challenges in the field and how technological advances might provide exciting new strategies to tackle these questions.This article is part of the themed issue 'Evo-devo in the genomics era, and the origins of morphological diversity'.
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Affiliation(s)
- Patrick Tschopp
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Clifford J Tabin
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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New Insights Into the Roles of Retinoic Acid Signaling in Nervous System Development and the Establishment of Neurotransmitter Systems. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 330:1-84. [PMID: 28215529 DOI: 10.1016/bs.ircmb.2016.09.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Secreted chiefly from the underlying mesoderm, the morphogen retinoic acid (RA) is well known to contribute to the specification, patterning, and differentiation of neural progenitors in the developing vertebrate nervous system. Furthermore, RA influences the subtype identity and neurotransmitter phenotype of subsets of maturing neurons, although relatively little is known about how these functions are mediated. This review provides a comprehensive overview of the roles played by RA signaling during the formation of the central and peripheral nervous systems of vertebrates and highlights its effects on the differentiation of several neurotransmitter systems. In addition, the evolutionary history of the RA signaling system is discussed, revealing both conserved properties and alternate modes of RA action. It is proposed that comparative approaches should be employed systematically to expand our knowledge of the context-dependent cellular mechanisms controlled by the multifunctional signaling molecule RA.
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46
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Madissoon E, Jouhilahti EM, Vesterlund L, Töhönen V, Krjutškov K, Petropoulous S, Einarsdottir E, Linnarsson S, Lanner F, Månsson R, Hovatta O, Bürglin TR, Katayama S, Kere J. Characterization and target genes of nine human PRD-like homeobox domain genes expressed exclusively in early embryos. Sci Rep 2016; 6:28995. [PMID: 27412763 PMCID: PMC4944136 DOI: 10.1038/srep28995] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 06/06/2016] [Indexed: 01/07/2023] Open
Abstract
PAIRED (PRD)-like homeobox genes belong to a class of predicted transcription factor genes. Several of these PRD-like homeobox genes have been predicted in silico from genomic sequence but until recently had no evidence of transcript expression. We found recently that nine PRD-like homeobox genes, ARGFX, CPHX1, CPHX2, DPRX, DUXA, DUXB, NOBOX, TPRX1 and TPRX2, were expressed in human preimplantation embryos. In the current study we characterized these PRD-like homeobox genes in depth and studied their functions as transcription factors. We cloned multiple transcript variants from human embryos and showed that the expression of these genes is specific to embryos and pluripotent stem cells. Overexpression of the genes in human embryonic stem cells confirmed their roles as transcription factors as either activators (CPHX1, CPHX2, ARGFX) or repressors (DPRX, DUXA, TPRX2) with distinct targets that could be explained by the amino acid sequence in homeodomain. Some PRD-like homeodomain transcription factors had high concordance of target genes and showed enrichment for both developmentally important gene sets and a 36 bp DNA recognition motif implicated in Embryo Genome Activation (EGA). Our data implicate a role for these previously uncharacterized PRD-like homeodomain proteins in the regulation of human embryo genome activation and preimplantation embryo development.
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Affiliation(s)
- Elo Madissoon
- Biosciences and Nutrition, Karolinska Institutet, Huddinge, Stockholm, Sweden
| | | | | | - Virpi Töhönen
- Biosciences and Nutrition, Karolinska Institutet, Huddinge, Stockholm, Sweden
| | - Kaarel Krjutškov
- Biosciences and Nutrition, Karolinska Institutet, Huddinge, Stockholm, Sweden
- Competence Centre on Health Technologies, Tartu, Estonia
| | - Sophie Petropoulous
- Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institutet, Huddinge, Stockholm, Sweden
| | - Elisabet Einarsdottir
- Biosciences and Nutrition, Karolinska Institutet, Huddinge, Stockholm, Sweden
- Molecular Neurology Research Program, University of Helsinki and Folkhälsan Institute of Genetics, Helsinki, Finland
| | - Sten Linnarsson
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden
| | - Fredrik Lanner
- Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institutet, Huddinge, Stockholm, Sweden
| | - Robert Månsson
- Department of Laboratory Medicine, Division of Clinical Immunology, Karolinska Institutet, Huddinge, Stockholm, Sweden
| | - Outi Hovatta
- Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institutet, Huddinge, Stockholm, Sweden
| | | | - Shintaro Katayama
- Biosciences and Nutrition, Karolinska Institutet, Huddinge, Stockholm, Sweden
| | - Juha Kere
- Biosciences and Nutrition, Karolinska Institutet, Huddinge, Stockholm, Sweden
- Molecular Neurology Research Program, University of Helsinki and Folkhälsan Institute of Genetics, Helsinki, Finland
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Timoshevskiy VA, Herdy JR, Keinath MC, Smith JJ. Cellular and Molecular Features of Developmentally Programmed Genome Rearrangement in a Vertebrate (Sea Lamprey: Petromyzon marinus). PLoS Genet 2016; 12:e1006103. [PMID: 27341395 PMCID: PMC4920378 DOI: 10.1371/journal.pgen.1006103] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 05/13/2016] [Indexed: 11/21/2022] Open
Abstract
The sea lamprey (Petromyzon marinus) represents one of the few vertebrate species known to undergo large-scale programmatic elimination of genomic DNA over the course of its normal development. Programmed genome rearrangements (PGRs) result in the reproducible loss of ~20% of the genome from somatic cell lineages during early embryogenesis. Studies of PGR hold the potential to provide novel insights related to the maintenance of genome stability during the cell cycle and coordination between mechanisms responsible for the accurate distribution of chromosomes into daughter cells, yet little is known regarding the mechanistic basis or cellular context of PGR in this or any other vertebrate lineage. Here we identify epigenetic silencing events that are associated with the programmed elimination of DNA and describe the spatiotemporal dynamics of PGR during lamprey embryogenesis. In situ analyses reveal that the earliest DNA methylation (and to some extent H3K9 trimethylation) events are limited to specific extranuclear structures (micronuclei) containing eliminated DNA. During early embryogenesis a majority of micronuclei (~60%) show strong enrichment for repressive chromatin modifications (H3K9me3 and 5meC). These analyses also led to the discovery that eliminated DNA is packaged into chromatin that does not migrate with somatically retained chromosomes during anaphase, a condition that is superficially similar to lagging chromosomes observed in some cancer subtypes. Closer examination of “lagging” chromatin revealed distributions of repetitive elements, cytoskeletal contacts and chromatin contacts that provide new insights into the cellular mechanisms underlying the programmed loss of these segments. Our analyses provide additional perspective on the cellular and molecular context of PGR, identify new structures associated with elimination of DNA and reveal that PGR is completed over the course of several successive cell divisions. Lampreys possess a fascinating genome biology wherein large portions of the genome, including large numbers of genes, are programmatically deleted during development. The lamprey therefore represents a uniquely informative system with respect to several broad areas of biology, including genome stability/rearrangement, epigenetic silencing, and the establishment and maintenance of pluripotency. However, little is known regarding the cellular context or mechanism of deletion, partly due to the challenges of observing rearrangements in situ. Here we present analyses and new techniques that significantly advance our understanding of the subcellular context of programmed rearrangements and interactions between programmed deletion and canonical DNA silencing mechanisms. These analyses demonstrate that DNA elimination occurs earlier in embryogenesis than was previously recognized and reveal several new cellular and molecular aspects of programmed DNA loss. Specifically we show that eliminated DNA exhibits a unique migration pattern during cell division, is packaged into discreet subcellular structures later in the cell cycle, and undergoes epigenetic silencing through DNA and histone methylation. These observations provide new insight into the mechanisms underlying programmed DNA loss and suggest a functional link between programmed DNA loss and other, more conserved gene silencing pathways.
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Affiliation(s)
| | - Joseph R. Herdy
- Department of Biology, University of Kentucky, Lexington, Kentucky, United States of America
- Laboratory of Genetics, The Salk Institute, La Jolla, California, United States of America
| | - Melissa C. Keinath
- Department of Biology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Jeramiah J. Smith
- Department of Biology, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail:
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Miyashita T, Diogo R. Evolution of Serial Patterns in the Vertebrate Pharyngeal Apparatus and Paired Appendages via Assimilation of Dissimilar Units. Front Ecol Evol 2016. [DOI: 10.3389/fevo.2016.00071] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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Parker HJ, Bronner ME, Krumlauf R. The vertebrate Hox gene regulatory network for hindbrain segmentation: Evolution and diversification: Coupling of a Hox gene regulatory network to hindbrain segmentation is an ancient trait originating at the base of vertebrates. Bioessays 2016; 38:526-38. [PMID: 27027928 DOI: 10.1002/bies.201600010] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hindbrain development is orchestrated by a vertebrate gene regulatory network that generates segmental patterning along the anterior-posterior axis via Hox genes. Here, we review analyses of vertebrate and invertebrate chordate models that inform upon the evolutionary origin and diversification of this network. Evidence from the sea lamprey reveals that the hindbrain regulatory network generates rhombomeric compartments with segmental Hox expression and an underlying Hox code. We infer that this basal feature was present in ancestral vertebrates and, as an evolutionarily constrained developmental state, is fundamentally important for patterning of the vertebrate hindbrain across diverse lineages. Despite the common ground plan, vertebrates exhibit neuroanatomical diversity in lineage-specific patterns, with different vertebrates revealing variations of Hox expression in the hindbrain that could underlie this diversification. Invertebrate chordates lack hindbrain segmentation but exhibit some conserved aspects of this network, with retinoic acid signaling playing a role in establishing nested domains of Hox expression.
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Affiliation(s)
- Hugo J Parker
- Stowers Institute for Medical Research, Kansas City, MO, USA
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Robb Krumlauf
- Stowers Institute for Medical Research, Kansas City, MO, USA.,Department of Anatomy and Cell Biology, Kansas University Medical Center, Kansas City, KS, USA
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Evolution of mammalian sound localization circuits: A developmental perspective. Prog Neurobiol 2016; 141:1-24. [PMID: 27032475 DOI: 10.1016/j.pneurobio.2016.02.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Revised: 02/27/2016] [Accepted: 02/27/2016] [Indexed: 01/06/2023]
Abstract
Localization of sound sources is a central aspect of auditory processing. A unique feature of mammals is the smooth, tonotopically organized extension of the hearing range to high frequencies (HF) above 10kHz, which likely induced positive selection for novel mechanisms of sound localization. How this change in the auditory periphery is accompanied by changes in the central auditory system is unresolved. I will argue that the major VGlut2(+) excitatory projection neurons of sound localization circuits (dorsal cochlear nucleus (DCN), lateral and medial superior olive (LSO and MSO)) represent serial homologs with modifications, thus being paramorphs. This assumption is based on common embryonic origin from an Atoh1(+)/Wnt1(+) cell lineage in the rhombic lip of r5, same cell birth, a fusiform cell morphology, shared genetic components such as Lhx2 and Lhx9 transcription factors, and similar projection patterns. Such a parsimonious evolutionary mechanism likely accelerated the emergence of neurons for sound localization in all three dimensions. Genetic analyses indicate that auditory nuclei in fish, birds, and mammals receive contributions from the same progenitor lineages. Anatomical and physiological differences and the independent evolution of tympanic ears in vertebrate groups, however, argue for convergent evolution of sound localization circuits in tetrapods (amphibians, reptiles, birds, and mammals). These disparate findings are discussed in the context of the genetic architecture of the developing hindbrain, which facilitates convergent evolution. Yet, it will be critical to decipher the gene regulatory networks underlying development of auditory neurons across vertebrates to explore the possibility of homologous neuronal populations.
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