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Castillo H, Hanna P, Sachs LM, Buisine N, Godoy F, Gilbert C, Aguilera F, Muñoz D, Boisvert C, Debiais-Thibaud M, Wan J, Spicuglia S, Marcellini S. Xenopus tropicalis osteoblast-specific open chromatin regions reveal promoters and enhancers involved in human skeletal phenotypes and shed light on early vertebrate evolution. Cells Dev 2024:203924. [PMID: 38692409 DOI: 10.1016/j.cdev.2024.203924] [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: 03/09/2024] [Revised: 04/18/2024] [Accepted: 04/26/2024] [Indexed: 05/03/2024]
Abstract
While understanding the genetic underpinnings of osteogenesis has far-reaching implications for skeletal diseases and evolution, a comprehensive characterization of the osteoblastic regulatory landscape in non-mammalian vertebrates is still lacking. Here, we compared the ATAC-Seq profile of Xenopus tropicalis (Xt) osteoblasts to a variety of non mineralizing control tissues, and identified osteoblast-specific nucleosome free regions (NFRs) at 527 promoters and 6747 distal regions. Sequence analyses, Gene Ontology, RNA-Seq and ChIP-Seq against four key histone marks confirmed that the distal regions correspond to bona fide osteogenic transcriptional enhancers exhibiting a shared regulatory logic with mammals. We report 425 regulatory regions conserved with human and globally associated to skeletogenic genes. Of these, 35 regions have been shown to impact human skeletal phenotypes by GWAS, including one trps1 enhancer and the runx2 promoter, two genes which are respectively involved in trichorhinophalangeal syndrome type I and cleidocranial dysplasia. Intriguingly, 60 osteoblastic NFRs also align to the genome of the elephant shark, a species lacking osteoblasts and bone tissue. To tackle this paradox, we chose to focus on dlx5 because its conserved promoter, known to integrate regulatory inputs during mammalian osteogenesis, harbours an osteoblast-specific NFR in both frog and human. Hence, we show that dlx5 is expressed in Xt and elephant shark odontoblasts, supporting a common cellular and genetic origin of bone and dentine. Taken together, our work (i) unravels the Xt osteogenic regulatory landscape, (ii) illustrates how cross-species comparisons harvest data relevant to human biology and (iii) reveals that a set of genes including bnc2, dlx5, ebf3, mir199a, nfia, runx2 and zfhx4 drove the development of a primitive form of mineralized skeletal tissue deep in the vertebrate lineage.
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Affiliation(s)
- Héctor Castillo
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile.
| | - Patricia Hanna
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - Laurent M Sachs
- UMR7221, Physiologie Moléculaire et Adaptation, CNRS, MNHN, Paris Cedex 05, France
| | - Nicolas Buisine
- UMR7221, Physiologie Moléculaire et Adaptation, CNRS, MNHN, Paris Cedex 05, France
| | - Francisco Godoy
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - Clément Gilbert
- Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, 12 route 128, 91190 Gif-sur-Yvette, France
| | - Felipe Aguilera
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - David Muñoz
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - Catherine Boisvert
- School of Molecular and Life Sciences, Curtin University, Perth, WA, Australia
| | - Mélanie Debiais-Thibaud
- Institut des Sciences de l'Evolution de Montpellier, ISEM, Univ Montpellier, CNRS, IRD, Montpellier, France
| | - Jing Wan
- Aix-Marseille University, INSERM, TAGC, UMR 1090, Marseille, France; Equipe Labelisée LIGUE contre le Cancer, Marseille, France
| | - Salvatore Spicuglia
- Aix-Marseille University, INSERM, TAGC, UMR 1090, Marseille, France; Equipe Labelisée LIGUE contre le Cancer, Marseille, France
| | - Sylvain Marcellini
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile.
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2
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MacKenzie EM, Atkins JB, Korneisel DE, Cantelon AS, McKinnell IW, Maddin HC. Normal development in Xenopus laevis: A complementary staging table for the skull based on cartilage and bone. Dev Dyn 2022; 251:1340-1356. [PMID: 35247013 DOI: 10.1002/dvdy.465] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 02/10/2022] [Accepted: 02/15/2022] [Indexed: 11/07/2022] Open
Abstract
BACKGROUND Xenopus laevis is a widely used model organism in the fields of genetics and development, and more recently evolution. At present, the most widely used staging table for X. laevis is based primarily on external features and does not describe the corresponding skull development in detail. Here, we describe skull development in X. laevis, complete with labelled figures, for each relevant stage in the most widely used staging table. RESULTS We find skull development in X. laevis is, for the most part, distinct at each of the previously established stages based on external anatomy. However, variation does exist in the timing of onset of ossification of certain bones in the skull, which results in a range of stages where a skull element first ossifies. The overall sequence of ossification is less variable than the timing of ossification onset. CONCLUSIONS While events in skull development vary somewhat between specimens, and in comparison, to external events, this staging table is useful in showing both when bones first appear and for documenting the range of temporal variance in X. laevis skull development more accurately than previously done. Furthermore, when only skull data is available, the approximate stage of a specimen can now be determined. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Erin M MacKenzie
- Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
| | - Jade B Atkins
- Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
| | - Dana E Korneisel
- Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
| | - Alanna S Cantelon
- Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
| | - Iain W McKinnell
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Hillary C Maddin
- Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada
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3
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Nguyen JKB, Eames BF. Evolutionary repression of chondrogenic genes in the vertebrate osteoblast. FEBS J 2020; 287:4354-4361. [PMID: 31994313 DOI: 10.1111/febs.15228] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Revised: 12/30/2019] [Accepted: 01/24/2020] [Indexed: 12/12/2022]
Abstract
Gene expression in extant animals might reveal how skeletal cells have evolved over the past 500 million years. The cells that make up cartilage (chondrocytes) and bone (osteoblasts) express many of the same genes, but they also have important molecular differences that allow us to distinguish them as separate cell types. For example, traditional studies of later-diverged vertebrates, such as mouse and chick, defined the genes Col2a1 and sex-determining region Y-box 9 as cartilage-specific. However, recent studies have shown that osteoblasts of earlier-diverged vertebrates, such as frog, gar, and zebrafish, express these 'chondrogenic' markers. In this review, we examine the resulting hypothesis that chondrogenic gene expression became repressed in osteoblasts over evolutionary time. The amphibian is an underexplored skeletal model that is uniquely positioned to address this hypothesis, especially given that it diverged when life transitioned from water to land. Given the relationship between phylogeny and ontogeny, a novel discovery for skeletal cell evolution might bolster our understanding of skeletal cell development.
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Affiliation(s)
- Jason K B Nguyen
- Department of Anatomy, Physiology, and Pharmacology, University of Saskatchewan, Saskatoon, Canada
| | - B Frank Eames
- Department of Anatomy, Physiology, and Pharmacology, University of Saskatchewan, Saskatoon, Canada
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Muñoz D, Castillo H, Henríquez JP, Marcellini S. Bone regeneration after traumatic skull injury in Xenopus tropicalis. Mech Dev 2018; 154:153-161. [PMID: 30420272 DOI: 10.1016/j.mod.2018.06.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 06/29/2018] [Accepted: 06/30/2018] [Indexed: 10/28/2022]
Abstract
The main purpose of regenerative biology is to improve human health by exploiting cellular and molecular mechanisms favoring tissue repair. In recent years, non-mammalian vertebrates have emerged as powerful model organisms to tackle the problem of tissue regeneration. Here, we analyze the process of bone repair in metamorphosing Xenopus tropicalis tadpoles subjected to traumatic skull injury. Five days after skull perforation, a dense and highly vascularized mesenchymal is apparent over the injury site. Using an in vivo bone staining procedure based on independent pulses of Alizarin red and Calcein green, we show that the deposition of new bone matrix completely closes the wound in 15 days. The absence of cartilage implies that bone repair follows an intramembranous ossification route. Collagen second harmonic imaging reveals that while a well-organized lamellar type of bone is deposited during development, a woven type of bone is produced during the early-phase of the regeneration process. Osteoblasts lying against the regenerating bone robustly express fibrillar collagen 1a1, SPARC and Dlx5. These analyses establish Xenopus tropicalis as a new model system to improve traumatic skull injury recovery.
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Affiliation(s)
- David Muñoz
- Group for the Study of Developmental Processes (GDeP), Department of Cell Biology, Faculty of Biological Sciences, University of Concepción, Chile; Laboratory of Development and Evolution (LADE), University of Concepción, Chile
| | - Héctor Castillo
- Group for the Study of Developmental Processes (GDeP), Department of Cell Biology, Faculty of Biological Sciences, University of Concepción, Chile; Laboratory of Development and Evolution (LADE), University of Concepción, Chile
| | - Juan Pablo Henríquez
- Group for the Study of Developmental Processes (GDeP), Department of Cell Biology, Faculty of Biological Sciences, University of Concepción, Chile; Center for Advanced Microscopy (CMA Bio-Bio), University of Concepción, Chile
| | - Sylvain Marcellini
- Group for the Study of Developmental Processes (GDeP), Department of Cell Biology, Faculty of Biological Sciences, University of Concepción, Chile; Laboratory of Development and Evolution (LADE), University of Concepción, Chile.
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Evolutionary origin of endochondral ossification: the transdifferentiation hypothesis. Dev Genes Evol 2016; 227:121-127. [DOI: 10.1007/s00427-016-0567-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 11/23/2016] [Indexed: 02/06/2023]
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Fritz A, Bertin A, Hanna P, Nualart F, Marcellini S. A Single Chance to Contact Multiple Targets: Distinct Osteocyte Morphotypes Shed Light on the Cellular Mechanism Ensuring the Robust Formation of Osteocytic Networks. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2016; 326:280-9. [PMID: 27381191 DOI: 10.1002/jez.b.22683] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Revised: 06/03/2016] [Accepted: 06/10/2016] [Indexed: 01/16/2023]
Abstract
The formation of the complex osteocytic network relies on the emission of long cellular processes involved in communication, mechanical strain sensing, and bone turnover control. Newly deposited osteocytic processes rapidly become trapped within the calcifying matrix, and, therefore, they must adopt their definitive conformation and contact their targets in a single morphogenetic event. However, the cellular mechanisms ensuring the robustness of this unique mode of morphogenesis remain unknown. To address this issue, we examined the developing calvaria of the amphibian Xenopus tropicalis by confocal, two-photon, and super-resolution imaging, and described flattened osteocytes lying within a woven bone structured in lamellae of randomly oriented collagen fibers. While most cells emit peripheral and perpendicular processes, we report two osteocytes morphotypes, located at different depth within the bone matrix and exhibiting distinct number and orientation of perpendicular cell processes. We show that this pattern is conserved with the chick Gallus gallus and suggest that the cellular microenvironment, and more particularly cell-cell contact, plays a fundamental role in the induction and stabilization of osteocytic processes. We propose that this intrinsic property might have been evolutionarily selected for its ability to robustly generate self-organizing osteocytic networks harbored by the wide variety of bone shapes and architectures found in extant and extinct vertebrates.
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Affiliation(s)
- Alan Fritz
- Laboratory of Development and Evolution, Department of Cell Biology, Faculty of Biological Sciences, University of Concepcion, Concepción, Chile
| | - Ariana Bertin
- Laboratory of Development and Evolution, Department of Cell Biology, Faculty of Biological Sciences, University of Concepcion, Concepción, Chile
| | - Patricia Hanna
- Laboratory of Development and Evolution, Department of Cell Biology, Faculty of Biological Sciences, University of Concepcion, Concepción, Chile
| | - Francisco Nualart
- Center for Advanced Microscopy (CMA Bio-Bio), University of Concepcion, Concepción, Chile
| | - Sylvain Marcellini
- Laboratory of Development and Evolution, Department of Cell Biology, Faculty of Biological Sciences, University of Concepcion, Concepción, Chile
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Taatjes DJ, Roth J. The Histochemistry and Cell Biology omnium-gatherum: the year 2015 in review. Histochem Cell Biol 2016; 145:239-74. [DOI: 10.1007/s00418-016-1417-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/01/2016] [Indexed: 02/07/2023]
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8
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Cristofori-Armstrong B, Soh MS, Talwar S, Brown DL, Griffin JDO, Dekan Z, Stow JL, King GF, Lynch JW, Rash LD. Xenopus borealis as an alternative source of oocytes for biophysical and pharmacological studies of neuronal ion channels. Sci Rep 2015; 5:14763. [PMID: 26440210 PMCID: PMC4594035 DOI: 10.1038/srep14763] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 09/07/2015] [Indexed: 01/10/2023] Open
Abstract
For the past 30 years, oocytes from Xenopus laevis have been extensively used to express and characterise ion channels in an easily controlled environment. Here we report the first use of oocytes from the closely related species Xenopus borealis as an alternative expression system for neuronal ion channels. Using the two-electrode voltage-clamp technique, we show that a wide variety of voltage- and ligand-gated ion channels have the same channel properties and pharmacological profiles when expressed in either X. laevis or X. borealis oocytes. Potential advantages of the X. borealis oocytes include a smaller endogenous chloride current and the ability to produce more intense fluorescence signals when studied with voltage-clamp fluorometry. Scanning electron microscopy revealed a difference in vitelline membrane structure between the two species, which may be related to the discrepancy in fluorescence signals observed. We demonstrate that X. borealis oocytes are a viable heterologous system for expression of neuronal ion channels with some potential advantages over X. laevis oocytes for certain applications.
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Affiliation(s)
| | - Ming S Soh
- Queensland Brain Institute, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Sahil Talwar
- Queensland Brain Institute, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Darren L Brown
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - John D O Griffin
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Zoltan Dekan
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Jennifer L Stow
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Glenn F King
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, St Lucia, QLD 4072, Australia.,School of Biomedical Sciences, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Lachlan D Rash
- Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
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9
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Enault S, Muñoz DN, Silva WTAF, Borday-Birraux V, Bonade M, Oulion S, Ventéo S, Marcellini S, Debiais-Thibaud M. Molecular footprinting of skeletal tissues in the catshark Scyliorhinus canicula and the clawed frog Xenopus tropicalis identifies conserved and derived features of vertebrate calcification. Front Genet 2015; 6:283. [PMID: 26442101 PMCID: PMC4584932 DOI: 10.3389/fgene.2015.00283] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 08/24/2015] [Indexed: 12/22/2022] Open
Abstract
Understanding the evolutionary emergence and subsequent diversification of the vertebrate skeleton requires a comprehensive view of the diverse skeletal cell types found in distinct developmental contexts, tissues, and species. To date, our knowledge of the molecular nature of the shark calcified extracellular matrix, and its relationships with osteichthyan skeletal tissues, remain scarce. Here, based on specific combinations of expression patterns of the Col1a1, Col1a2, and Col2a1 fibrillar collagen genes, we compare the molecular footprint of endoskeletal elements from the chondrichthyan Scyliorhinus canicula and the tetrapod Xenopus tropicalis. We find that, depending on the anatomical location, Scyliorhinus skeletal calcification is associated to cell types expressing different subsets of fibrillar collagen genes, such as high levels of Col1a1 and Col1a2 in the neural arches, high levels of Col2a1 in the tesserae, or associated to a drastic Col2a1 downregulation in the centrum. We detect low Col2a1 levels in Xenopus osteoblasts, thereby revealing that the osteoblastic expression of this gene was significantly reduced in the tetrapod lineage. Finally, we uncover a striking parallel, from a molecular and histological perspective, between the vertebral cartilage calcification of both species and discuss the evolutionary origin of endochondral ossification.
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Affiliation(s)
- Sébastien Enault
- Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, Centre National de la Recherche Scientifique, IRD, EPHE Montpellier, France
| | - David N Muñoz
- Laboratory of Development and Evolution, Department of Cell Biology, Faculty of Biological Sciences, Universidad de Concepción Concepción, Chile
| | - Willian T A F Silva
- Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, Centre National de la Recherche Scientifique, IRD, EPHE Montpellier, France
| | - Véronique Borday-Birraux
- Laboratoire EGCE UMR Centre National de la Recherche Scientifique 9191, IRD247, Université Paris Sud Gif-sur-Yvette, France ; Université Paris Diderot, Sorbonne Paris Cité Paris, France
| | - Morgane Bonade
- Laboratoire EGCE UMR Centre National de la Recherche Scientifique 9191, IRD247, Université Paris Sud Gif-sur-Yvette, France
| | - Silvan Oulion
- Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, Centre National de la Recherche Scientifique, IRD, EPHE Montpellier, France
| | - Stéphanie Ventéo
- Institute for Neurosciences of Montpellier, Institut National de la Santé et de la Recherche Médicale U1051 Montpellier, France
| | - Sylvain Marcellini
- Laboratory of Development and Evolution, Department of Cell Biology, Faculty of Biological Sciences, Universidad de Concepción Concepción, Chile
| | - Mélanie Debiais-Thibaud
- Institut des Sciences de l'Evolution de Montpellier, UMR5554, Université Montpellier, Centre National de la Recherche Scientifique, IRD, EPHE Montpellier, France
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10
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Ehnes DD, Price FD, Shrive NG, Hart DA, Rancourt DE, zur Nieden NI. Embryonic stem cell-derived osteocytes are capable of responding to mechanical oscillatory hydrostatic pressure. J Biomech 2015; 48:1915-21. [PMID: 25936968 DOI: 10.1016/j.jbiomech.2015.04.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 04/04/2015] [Accepted: 04/08/2015] [Indexed: 11/28/2022]
Abstract
Osteoblasts can be derived from embryonic stem cells (ESCs) by a 30 day differentiation process, whereupon cells spontaneously differentiate upon removal of LIF and respond to exogenously added 1,25α(OH)2 vitamin D3 with enhanced matrix mineralization. However, bone is a load-bearing tissue that has to perform under dynamic pressure changes during daily movement, a capacity that is executed by osteocytes. At present, it is unclear whether ESC-derived osteogenic cultures contain osteocytes and whether these are capable of responding to a relevant cyclic hydrostatic compression stimulus. Here, we show that ESC-osteoblastogenesis is followed by the generation of osteocytes and then mechanically load ESC-derived osteogenic cultures in a compression chamber using a cyclic loading protocol. Following mechanical loading of the cells, iNOS mRNA was upregulated 31-fold, which was consistent with a role for iNOS as an immediate early mechanoresponsive gene. Further analysis of matrix and bone-specific genes suggested a cellular response in favor of matrix remodeling. Immediate iNOS upregulation also correlated with a concomitant increase in Ctnnb1 and Tcf7l2 mRNAs along with increased nuclear TCF transcriptional activity, while the mRNA for the repressive Tcf7l1 was downregulated, providing a possible mechanistic explanation for the noted matrix remodeling. We conclude that ESC-derived osteocytes are capable of responding to relevant mechanical cues, at least such that mimic oscillatory compression stress, which not only provides new basic understanding, but also information that likely will be important for their use in cell-based regenerative therapies.
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Affiliation(s)
- D D Ehnes
- University of California Riverside, Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, 1113 Biological Sciences Building, Riverside, CA 92521, USA
| | - F D Price
- The Alberta Children's Hospital Research Institute, University of Calgary, Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1
| | - N G Shrive
- McCaig Institute for Bone and Joint Health, University of Calgary, Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1
| | - D A Hart
- McCaig Institute for Bone and Joint Health, University of Calgary, Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1
| | - D E Rancourt
- The Alberta Children's Hospital Research Institute, University of Calgary, Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1
| | - N I zur Nieden
- University of California Riverside, Department of Cell Biology & Neuroscience and Stem Cell Center, College of Natural and Agricultural Sciences, 1113 Biological Sciences Building, Riverside, CA 92521, USA; The Alberta Children's Hospital Research Institute, University of Calgary, Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1.
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