1
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Hardy H, Rainger J. Cell adhesion marker expression dynamics during fusion of the optic fissure. Gene Expr Patterns 2023; 50:119344. [PMID: 37844855 DOI: 10.1016/j.gep.2023.119344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 10/13/2023] [Accepted: 10/13/2023] [Indexed: 10/18/2023]
Abstract
Tissue fusion is a critical process that is repeated in multiple contexts during embryonic development and shares common attributes to processes such as wound healing and metastasis. Ocular coloboma is a developmental eye disorder that presents as a physical gap in the ventral eye, and is a major cause of childhood blindness. Coloboma results from fusion failure between opposing ventral retinal epithelia, but there are major knowledge gaps in our understanding of this process at the molecular and cell behavioural levels. Here we catalogue the expression of cell adhesion proteins: N-cadherin, E-cadherin, R-cadherin, ZO-1, and the EMT transcriptional activator and cadherin regulator SNAI2, in the developing chicken embryonic eye. We find that fusion pioneer cells at the edges of the fusing optic fissure have unique and dynamic expression profiles for N-cad, E-cad and ZO-1, and that these are temporally preceded by expression of SNAI2. This highlights the unique properties of these cells and indicates that regulation of cell adhesion factors may be a critical process in optic fissure closure.
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Affiliation(s)
- Holly Hardy
- The Division of Functional Genetics and Development, The Roslin Institute, Midlothian, EH25 9RG, UK
| | - Joe Rainger
- The Division of Functional Genetics and Development, The Roslin Institute, Midlothian, EH25 9RG, UK.
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2
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Bulk J, Kyrychenko V, Rensinghoff PM, Ghaderi Ardekani Z, Heermann S. Holoprosencephaly with a Special Form of Anophthalmia Result from Experimental Induction of bmp4, Oversaturating BMP Antagonists in Zebrafish. Int J Mol Sci 2023; 24:ijms24098052. [PMID: 37175759 PMCID: PMC10178349 DOI: 10.3390/ijms24098052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 04/18/2023] [Accepted: 04/27/2023] [Indexed: 05/15/2023] Open
Abstract
Vision is likely our most prominent sense and a correct development of the eye is at its basis. Early eye development is tightly connected to the development of the forebrain. A single eye field and the prospective telencephalon are situated within the anterior neural plate (ANP). During normal development, both domains are split and consecutively, two optic vesicles and two telencephalic lobes emerge. If this process is hampered, the domains remain condensed at the midline. The resulting developmental disorder is termed holoprosencephaly (HPE). The typical ocular finding associated with intense forms of HPE is cyclopia. However, also anophthalmia and coloboma can be associated with HPE. Here, we report that a correct balance of Bone morphogenetic proteins (BMPs) and their antagonists are important for forebrain and eye field cleavage. Experimental induction of a BMP ligand results in a severe form of HPE showing anophthalmia. We identified a dysmorphic forebrain containing retinal progenitors, which we termed crypt-oculoid. Optic vesicle evagination is impaired due to a loss of rx3 and, consecutively, of cxcr4a. Our data further suggest that the subduction of prospective hypothalamic cells during neurulation and neural keel formation is affected by the induction of a BMP ligand.
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Affiliation(s)
- Johannes Bulk
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany
| | - Valentyn Kyrychenko
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany
| | - Philipp M Rensinghoff
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany
| | - Zahra Ghaderi Ardekani
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany
| | - Stephan Heermann
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany
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3
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Trejo-Reveles V, Owen N, Ching Chan BH, Toms M, Schoenebeck JJ, Moosajee M, Rainger J. Identification of Novel Coloboma Candidate Genes through Conserved Gene Expression Analyses across Four Vertebrate Species. Biomolecules 2023; 13:293. [PMID: 36830662 PMCID: PMC9953556 DOI: 10.3390/biom13020293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 01/23/2023] [Accepted: 01/28/2023] [Indexed: 02/08/2023] Open
Abstract
Ocular coloboma (OC) is a failure of complete optic fissure closure during embryonic development and presents as a tissue defect along the proximal-distal axis of the ventral eye. It is classed as part of the clinical spectrum of structural eye malformations with microphthalmia and anophthalmia, collectively abbreviated to MAC. Despite deliberate attempts to identify causative variants in MAC, many patients remain without a genetic diagnosis. To reveal potential candidate genes, we utilised transcriptomes experimentally generated from embryonic eye tissues derived from humans, mice, zebrafish, and chicken at stages coincident with optic fissure closure. Our in-silico analyses found 10 genes with optic fissure-specific enriched expression: ALDH1A3, BMPR1B, EMX2, EPHB3, NID1, NTN1, PAX2, SMOC1, TENM3, and VAX1. In situ hybridization revealed that all 10 genes were broadly expressed ventrally in the developing eye but that only PAX2 and NTN1 were expressed in cells at the edges of the optic fissure margin. Of these conserved optic fissure genes, EMX2, NID1, and EPHB3 have not previously been associated with human MAC cases. Targeted genetic manipulation in zebrafish embryos using CRISPR/Cas9 caused the developmental MAC phenotype for emx2 and ephb3. We analysed available whole genome sequencing datasets from MAC patients and identified a range of variants with plausible causality. In combination, our data suggest that expression of genes involved in ventral eye development is conserved across a range of vertebrate species and that EMX2, NID1, and EPHB3 are candidate loci that warrant further functional analysis in the context of MAC and should be considered for sequencing in cohorts of patients with structural eye malformations.
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Affiliation(s)
- Violeta Trejo-Reveles
- Roslin Institute, R(D)SVS, Easter Bush Campus, University of Edinburgh, Edinburgh EH25 9RG, UK
| | - Nicholas Owen
- Development, Ageing and Disease, UCL Institute of Ophthalmology, London EC1V 9EL, UK
- Ocular Genomics and Therapeutics, The Francis Crick Institute, London NW1 1A, UK
| | - Brian Ho Ching Chan
- Roslin Institute, R(D)SVS, Easter Bush Campus, University of Edinburgh, Edinburgh EH25 9RG, UK
| | - Maria Toms
- Development, Ageing and Disease, UCL Institute of Ophthalmology, London EC1V 9EL, UK
- Ocular Genomics and Therapeutics, The Francis Crick Institute, London NW1 1A, UK
| | - Jeffrey J. Schoenebeck
- Roslin Institute, R(D)SVS, Easter Bush Campus, University of Edinburgh, Edinburgh EH25 9RG, UK
| | - Mariya Moosajee
- Development, Ageing and Disease, UCL Institute of Ophthalmology, London EC1V 9EL, UK
- Ocular Genomics and Therapeutics, The Francis Crick Institute, London NW1 1A, UK
- Department of Genetics, Moorfields Eye Hospital NHS Foundation Trust, London EC1V 2PD, UK
| | - Joe Rainger
- Roslin Institute, R(D)SVS, Easter Bush Campus, University of Edinburgh, Edinburgh EH25 9RG, UK
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4
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Boobalan E, Thompson AH, Alur RP, McGaughey DM, Dong L, Shih G, Vieta-Ferrer ER, Onojafe IF, Kalaskar VK, Arno G, Lotery AJ, Guan B, Bender C, Memon O, Brinster L, Soleilhavoup C, Panman L, Badea TC, Minella A, Lopez AJ, Thomasy SM, Moshiri A, Blain D, Hufnagel RB, Cogliati T, Bharti K, Brooks BP. Zfp503/Nlz2 Is Required for RPE Differentiation and Optic Fissure Closure. Invest Ophthalmol Vis Sci 2022; 63:5. [PMID: 36326727 PMCID: PMC9645360 DOI: 10.1167/iovs.63.12.5] [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] [Indexed: 11/06/2022] Open
Abstract
Purpose Uveal coloboma is a congenital eye malformation caused by failure of the optic fissure to close in early human development. Despite significant progress in identifying genes whose regulation is important for executing this closure, mutations are detected in a minority of cases using known gene panels, implying additional genetic complexity. We have previously shown knockdown of znf503 (the ortholog of mouse Zfp503) in zebrafish causes coloboma. Here we characterize Zfp503 knockout (KO) mice and evaluate transcriptomic profiling of mutant versus wild-type (WT) retinal pigment epithelium (RPE)/choroid. Methods Zfp503 KO mice were generated by gene targeting using homologous recombination. Embryos were characterized grossly and histologically. Patterns and level of developmentally relevant proteins/genes were examined with immunostaining/in situ hybridization. The transcriptomic profile of E11.5 KO RPE/choroid was compared to that of WT. Results Zfp503 is dynamically expressed in developing mouse eyes, and loss of its expression results in uveal coloboma. KO embryos exhibit altered mRNA levels and expression patterns of several key transcription factors involved in eye development, including Otx2, Mitf, Pax6, Pax2, Vax1, and Vax2, resulting in a failure to maintain the presumptive RPE, as evidenced by reduced melanin pigmentation and its differentiation into a neural retina-like lineage. Comparison of RNA sequencing data from WT and KO E11.5 embryos demonstrated reduced expression of melanin-related genes and significant overlap with genes known to be dynamically regulated at the optic fissure. Conclusions These results demonstrate a critical role of Zfp503 in maintaining RPE fate and optic fissure closure.
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Affiliation(s)
- Elangovan Boobalan
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Amy H. Thompson
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Ramakrishna P. Alur
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - David M. McGaughey
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Lijin Dong
- Mouse Genetic Engineering Core, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Grace Shih
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Emile R. Vieta-Ferrer
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Ighovie F. Onojafe
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Vijay K. Kalaskar
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Gavin Arno
- University College London Institute of Ophthalmology, London, United Kingdom,Moorfields Eye Hospital, London, United Kingdom
| | - Andrew J. Lotery
- Faculty of Medicine, University of Southampton, Southampton, United Kingdom
| | - Bin Guan
- Ophthalmic Genetics Laboratory, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Chelsea Bender
- Ophthalmic Genetics Laboratory, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Omar Memon
- Ocular and Stem Cell Translational Research Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Lauren Brinster
- Division of Veterinary Resources, Office of Research Services, National Institutes of Health, Bethesda, Maryland, United States
| | | | - Lia Panman
- MRC Toxicology Unit, University of Cambridge, Leicester, United Kingdom
| | - Tudor C. Badea
- Retinal Circuit Development and Genetics Unit, Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States,Research and Development Institute, Transilvania University of Brașov, Brașov, Romania,National Center for Brain Research, ICIA, Romanian Academy, Bucharest, România
| | - Andrea Minella
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California–Davis, Davis, California, United States
| | - Antonio Jacobo Lopez
- Department of Ophthalmology and Vision Science, School of Medicine, University of California–Davis, Davis, California, United States
| | - Sara M. Thomasy
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California–Davis, Davis, California, United States,Department of Ophthalmology and Vision Science, School of Medicine, University of California–Davis, Davis, California, United States
| | - Ala Moshiri
- Department of Ophthalmology and Vision Science, School of Medicine, University of California–Davis, Davis, California, United States
| | - Delphine Blain
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Robert B. Hufnagel
- Ophthalmic Genetics Laboratory, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Tiziana Cogliati
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Kapil Bharti
- Ocular and Stem Cell Translational Research Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Brian P. Brooks
- Pediatric, Developmental & Genetic Ophthalmology Section, Ophthalmic Genetics & Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
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5
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Cote LE, Feldman JL. Won't You be My Neighbor: How Epithelial Cells Connect Together to Build Global Tissue Polarity. Front Cell Dev Biol 2022; 10:887107. [PMID: 35800889 PMCID: PMC9253303 DOI: 10.3389/fcell.2022.887107] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 05/30/2022] [Indexed: 11/13/2022] Open
Abstract
Epithelial tissues form continuous barriers to protect against external environments. Within these tissues, epithelial cells build environment-facing apical membranes, junction complexes that anchor neighbors together, and basolateral surfaces that face other cells. Critically, to form a continuous apical barrier, neighboring epithelial cells must align their apico-basolateral axes to create global polarity along the entire tissue. Here, we will review mechanisms of global tissue-level polarity establishment, with a focus on how neighboring epithelial cells of different origins align their apical surfaces. Epithelial cells with different developmental origins and/or that polarize at different times and places must align their respective apico-basolateral axes. Connecting different epithelial tissues into continuous sheets or tubes, termed epithelial fusion, has been most extensively studied in cases where neighboring cells initially dock at an apical-to-apical interface. However, epithelial cells can also meet basal-to-basal, posing several challenges for apical continuity. Pre-existing basement membrane between the tissues must be remodeled and/or removed, the cells involved in docking are specialized, and new cell-cell adhesions are formed. Each of these challenges can involve changes to apico-basolateral polarity of epithelial cells. This minireview highlights several in vivo examples of basal docking and how apico-basolateral polarity changes during epithelial fusion. Understanding the specific molecular mechanisms of basal docking is an area ripe for further exploration that will shed light on complex morphogenetic events that sculpt developing organisms and on the cellular mechanisms that can go awry during diseases involving the formation of cysts, fistulas, atresias, and metastases.
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6
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Fox SC, Widen SA, Asai-Coakwell M, Havrylov S, Benson M, Prichard LB, Baddam P, Graf D, Lehmann OJ, Waskiewicz AJ. BMP3 is a novel locus involved in the causality of ocular coloboma. Hum Genet 2022; 141:1385-1407. [PMID: 35089417 DOI: 10.1007/s00439-022-02430-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Accepted: 01/04/2022] [Indexed: 12/29/2022]
Abstract
Coloboma, a congenital disorder characterized by gaps in ocular tissues, is caused when the choroid fissure fails to close during embryonic development. Several loci have been associated with coloboma, but these represent less than 40% of those that are involved with this disease. Here, we describe a novel coloboma-causing locus, BMP3. Whole exome sequencing and Sanger sequencing of patients with coloboma identified three variants in BMP3, two of which are predicted to be disease causing. Consistent with this, bmp3 mutant zebrafish have aberrant fissure closure. bmp3 is expressed in the ventral head mesenchyme and regulates phosphorylated Smad3 in a population of cells adjacent to the choroid fissure. Furthermore, mutations in bmp3 sensitize embryos to Smad3 inhibitor treatment resulting in open choroid fissures. Micro CT scans and Alcian blue staining of zebrafish demonstrate that mutations in bmp3 cause midface hypoplasia, suggesting that bmp3 regulates cranial neural crest cells. Consistent with this, we see active Smad3 in a population of periocular neural crest cells, and bmp3 mutant zebrafish have reduced neural crest cells in the choroid fissure. Taken together, these data suggest that Bmp3 controls Smad3 phosphorylation in neural crest cells to regulate early craniofacial and ocular development.
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Affiliation(s)
- Sabrina C Fox
- Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, AB, T6G 2E9, Canada.,Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Sonya A Widen
- Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, AB, T6G 2E9, Canada.,Vienna BioCenter, Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.,Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Mika Asai-Coakwell
- Department of Animal and Poultry and Animal Science, University of Saskatchewan, Saskatoon, SK, Canada.,Department of Ophthalmology, University of Alberta, Edmonton, AB, Canada
| | - Serhiy Havrylov
- Department of Medical Genetics, University of Alberta, Edmonton, AB, Canada.,Department of Ophthalmology, University of Alberta, Edmonton, AB, Canada
| | - Matthew Benson
- Department of Medical Genetics, University of Alberta, Edmonton, AB, Canada.,Department of Ophthalmology, University of Alberta, Edmonton, AB, Canada
| | - Lisa B Prichard
- Department of Biological Sciences, MacEwan University, Edmonton, AB, Canada
| | - Pranidhi Baddam
- Department of Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Daniel Graf
- Department of Medical Genetics, University of Alberta, Edmonton, AB, Canada.,Department of Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Ordan J Lehmann
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada.,Department of Medical Genetics, University of Alberta, Edmonton, AB, Canada.,Department of Ophthalmology, University of Alberta, Edmonton, AB, Canada
| | - Andrew J Waskiewicz
- Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, AB, T6G 2E9, Canada. .,Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada.
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7
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Knickmeyer MD, Mateo JL, Heermann S. BMP Signaling Interferes with Optic Chiasm Formation and Retinal Ganglion Cell Pathfinding in Zebrafish. Int J Mol Sci 2021; 22:ijms22094560. [PMID: 33925390 PMCID: PMC8123821 DOI: 10.3390/ijms22094560] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 04/19/2021] [Accepted: 04/24/2021] [Indexed: 11/17/2022] Open
Abstract
Decussation of axonal tracts is an important hallmark of vertebrate neuroanatomy resulting in one brain hemisphere controlling the contralateral side of the body and also computing the sensory information originating from that respective side. Here, we show that BMP interferes with optic chiasm formation and RGC pathfinding in zebrafish. Experimental induction of BMP4 at 15 hpf results in a complete ipsilateral projection of RGC axons and failure of commissural connections of the forebrain, in part as the result of an interaction with shh signaling, transcriptional regulation of midline guidance cues and an affected optic stalk morphogenesis. Experimental induction of BMP4 at 24 hpf, resulting in only a mild repression of forebrain shh ligand expression but in a broad expression of pax2a in the diencephalon, does not per se prevent RGC axons from crossing the midline. It nevertheless shows severe pathologies of RGC projections e.g., the fasciculation of RGC axons with the ipsilateral optic tract resulting in the innervation of one tectum by two eyes or the projection of RGC axons in the direction of the contralateral eye.
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Affiliation(s)
- Max D. Knickmeyer
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany;
- Faculty of Biology, University of Freiburg, Schaenzlestrasse 1, 79104 Freiburg, Germany
| | - Juan L. Mateo
- Departamento de Informática, Universidad de Oviedo, Jesús Arias de Velasco, 33005 Oviedo, Spain;
| | - Stephan Heermann
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Faculty of Medicine, University Freiburg, 79104 Freiburg, Germany;
- Correspondence:
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8
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Chan BHC, Moosajee M, Rainger J. Closing the Gap: Mechanisms of Epithelial Fusion During Optic Fissure Closure. Front Cell Dev Biol 2021; 8:620774. [PMID: 33505973 PMCID: PMC7829581 DOI: 10.3389/fcell.2020.620774] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 12/08/2020] [Indexed: 12/13/2022] Open
Abstract
A key embryonic process that occurs early in ocular development is optic fissure closure (OFC). This fusion process closes the ventral optic fissure and completes the circumferential continuity of the 3-dimensional eye. It is defined by the coming together and fusion of opposing neuroepithelia along the entire proximal-distal axis of the ventral optic cup, involving future neural retina, retinal pigment epithelium (RPE), optic nerve, ciliary body, and iris. Once these have occurred, cells within the fused seam differentiate into components of the functioning visual system. Correct development and progression of OFC, and the continued integrity of the fused margin along this axis, are important for the overall structure of the eye. Failure of OFC results in ocular coloboma-a significant cause of childhood visual impairment that can be associated with several complex ocular phenotypes including microphthalmia and anterior segment dysgenesis. Despite a large number of genes identified, the exact pathways that definitively mediate fusion have not yet been found, reflecting both the biological complexity and genetic heterogeneity of the process. This review will highlight how recent developmental studies have become focused specifically on the epithelial fusion aspects of OFC, applying a range of model organisms (spanning fish, avian, and mammalian species) and utilizing emerging high-resolution live-imaging technologies, transgenic fluorescent models, and unbiased transcriptomic analyses of segmentally-dissected fissure tissue. Key aspects of the fusion process are discussed, including basement membrane dynamics, unique cell behaviors, and the identities and fates of the cells that mediate fusion. These will be set in the context of what is now known, and how these point the way to new avenues of research.
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Affiliation(s)
- Brian Ho Ching Chan
- The Division of Functional Genetics and Development, The Royal Dick School of Veterinary Sciences, The Roslin Institute, The University of Edinburgh, Scotland, United Kingdom
| | - Mariya Moosajee
- University College London Institute of Ophthalmology, London, United Kingdom.,The Francis Crick Institute, London, United Kingdom.,Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom.,Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom
| | - Joe Rainger
- The Division of Functional Genetics and Development, The Royal Dick School of Veterinary Sciences, The Roslin Institute, The University of Edinburgh, Scotland, United Kingdom
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9
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Sun WR, Ramirez S, Spiller KE, Zhao Y, Fuhrmann S. Nf2 fine-tunes proliferation and tissue alignment during closure of the optic fissure in the embryonic mouse eye. Hum Mol Genet 2020; 29:3373-3387. [PMID: 33075808 DOI: 10.1093/hmg/ddaa228] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 09/29/2020] [Accepted: 10/12/2020] [Indexed: 11/14/2022] Open
Abstract
Uveal coloboma represents one of the most common congenital ocular malformations accounting for up to 10% of childhood blindness (~1 in 5000 live birth). Coloboma originates from defective fusion of the optic fissure (OF), a transient gap that forms during eye morphogenesis by asymmetric, ventral invagination. Genetic heterogeneity combined with the activity of developmentally regulated genes suggests multiple mechanisms regulating OF closure. The tumor suppressor and FERM domain protein Neurofibromin 2 (NF2) controls diverse processes in cancer, development and regeneration, via Hippo pathway and cytoskeleton regulation. In humans, NF2 mutations can cause ocular abnormalities, including coloboma, however, its actual role in OF closure is unknown. Using conditional inactivation in the embryonic mouse eye, our data indicate that loss of Nf2 function results in a novel underlying cause for coloboma. In particular, mutant eyes show substantially increased retinal pigmented epithelium (RPE) proliferation in the fissure region with concomitant acquisition of RPE cell fate. Cells lining the OF margin can maintain RPE fate ectopically and fail to transition from neuroepithelial to cuboidal shape. In the dorsal RPE of the optic cup, Nf2 inactivation leads to a robust increase in cell number, with local disorganization of the cytoskeleton components F-actin and pMLC2. We propose that RPE hyperproliferation is the primary cause for the observed defects causing insufficient alignment of the OF margins in Nf2 mutants and failure to fuse properly, resulting in persistent coloboma. Our findings indicate that limiting proliferation particularly in the RPE layer is a critical mechanism during OF closure.
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Affiliation(s)
- Wesley R Sun
- Department of Ophthalmology and Visual Sciences, VEI, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Sara Ramirez
- Department of Ophthalmology and Visual Sciences, VEI, Vanderbilt University Medical Center, Nashville, TN 37232, USA.,Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37240, USA
| | - Kelly E Spiller
- Department of Ophthalmology and Visual Sciences, VEI, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Yan Zhao
- Department of Ophthalmology and Visual Sciences, VEI, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Sabine Fuhrmann
- Department of Ophthalmology and Visual Sciences, VEI, Vanderbilt University Medical Center, Nashville, TN 37232, USA.,Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37240, USA
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10
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Yoon KH, Fox SC, Dicipulo R, Lehmann OJ, Waskiewicz AJ. Ocular coloboma: Genetic variants reveal a dynamic model of eye development. AMERICAN JOURNAL OF MEDICAL GENETICS PART C-SEMINARS IN MEDICAL GENETICS 2020; 184:590-610. [PMID: 32852110 DOI: 10.1002/ajmg.c.31831] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2020] [Revised: 07/27/2020] [Accepted: 07/28/2020] [Indexed: 12/21/2022]
Abstract
Ocular coloboma is a congenital disorder of the eye where a gap exists in the inferior retina, lens, iris, or optic nerve tissue. With a prevalence of 2-19 per 100,000 live births, coloboma, and microphthalmia, an associated ocular disorder, represent up to 10% of childhood blindness. It manifests due to the failure of choroid fissure closure during eye development, and it is a part of a spectrum of ocular disorders that include microphthalmia and anophthalmia. Use of genetic approaches from classical pedigree analyses to next generation sequencing has identified more than 40 loci that are associated with the causality of ocular coloboma. As we have expanded studies to include singleton cases, hereditability has been very challenging to prove. As such, researchers over the past 20 years, have unraveled the complex interrelationship amongst these 40 genes using vertebrate model organisms. Such research has greatly increased our understanding of eye development. These genes function to regulate initial specification of the eye field, migration of retinal precursors, patterning of the retina, neural crest cell biology, and activity of head mesoderm. This review will discuss the discovery of loci using patient data, their investigations in animal models, and the recent advances stemming from animal models that shed new light in patient diagnosis.
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Affiliation(s)
- Kevin H Yoon
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Women & Children's Health Research Institute, University of Alberta, Edmonton, Canada
| | - Sabrina C Fox
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Women & Children's Health Research Institute, University of Alberta, Edmonton, Canada
| | - Renée Dicipulo
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Women & Children's Health Research Institute, University of Alberta, Edmonton, Canada
| | - Ordan J Lehmann
- Women & Children's Health Research Institute, University of Alberta, Edmonton, Canada.,Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada.,Department of Ophthalmology, University of Alberta, Edmonton, Alberta, Canada
| | - Andrew J Waskiewicz
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Women & Children's Health Research Institute, University of Alberta, Edmonton, Canada
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