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Miles KD, Barker CM, Russell KP, Appel BH, Doll CA. Electrical Synapses Mediate Embryonic Hyperactivity in a Zebrafish Model of Fragile X Syndrome. J Neurosci 2024; 44:e2275232024. [PMID: 38969506 PMCID: PMC11293453 DOI: 10.1523/jneurosci.2275-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 06/19/2024] [Accepted: 06/27/2024] [Indexed: 07/07/2024] Open
Abstract
Although hyperactivity is associated with a wide variety of neurodevelopmental disorders, the early embryonic origins of locomotion have hindered investigation of pathogenesis of these debilitating behaviors. The earliest motor output in vertebrate animals is generated by clusters of early-born motor neurons (MNs) that occupy distinct regions of the spinal cord, innervating stereotyped muscle groups. Gap junction electrical synapses drive early spontaneous behavior in zebrafish, prior to the emergence of chemical neurotransmitter networks. We use a genetic model of hyperactivity to gain critical insight into the consequences of errors in motor circuit formation and function, finding that Fragile X syndrome model mutant zebrafish are hyperexcitable from the earliest phases of spontaneous behavior, show altered sensitivity to blockade of electrical gap junctions, and have increased expression of the gap junction protein Connexin 34/35. We further show that this hyperexcitable behavior can be rescued by pharmacological inhibition of electrical synapses. We also use functional imaging to examine MN and interneuron (IN) activity in early embryogenesis, finding genetic disruption of electrical gap junctions uncouples activity between mnx1 + MNs and INs. Taken together, our work highlights the importance of electrical synapses in motor development and suggests that the origins of hyperactivity in neurodevelopmental disorders may be established during the initial formation of locomotive circuits.
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Affiliation(s)
- Kaleb D Miles
- Section of Developmental Biology, Department of Pediatrics, Children's Hospital Colorado, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045
| | - Chase M Barker
- Section of Developmental Biology, Department of Pediatrics, Children's Hospital Colorado, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045
| | - Kristen P Russell
- Section of Developmental Biology, Department of Pediatrics, Children's Hospital Colorado, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045
| | - Bruce H Appel
- Section of Developmental Biology, Department of Pediatrics, Children's Hospital Colorado, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045
| | - Caleb A Doll
- Section of Developmental Biology, Department of Pediatrics, Children's Hospital Colorado, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045
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Lukowicz-Bedford RM, Eisen JS, Miller AC. Gap-junction-mediated bioelectric signaling required for slow muscle development and function in zebrafish. Curr Biol 2024; 34:3116-3132.e5. [PMID: 38936363 PMCID: PMC11265983 DOI: 10.1016/j.cub.2024.06.007] [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: 01/04/2024] [Revised: 04/11/2024] [Accepted: 06/04/2024] [Indexed: 06/29/2024]
Abstract
Bioelectric signaling, intercellular communication facilitated by membrane potential and electrochemical coupling, is emerging as a key regulator of animal development. Gap junction (GJ) channels can mediate bioelectric signaling by creating a fast, direct pathway between cells for the movement of ions and other small molecules. In vertebrates, GJ channels are formed by a highly conserved transmembrane protein family called the connexins. The connexin gene family is large and complex, creating challenges in identifying specific connexins that create channels within developing and mature tissues. Using the embryonic zebrafish neuromuscular system as a model, we identify a connexin conserved across vertebrate lineages, gjd4, which encodes the Cx46.8 protein, that mediates bioelectric signaling required for slow muscle development and function. Through mutant analysis and in vivo imaging, we show that gjd4/Cx46.8 creates GJ channels specifically in developing slow muscle cells. Using genetics, pharmacology, and calcium imaging, we find that spinal-cord-generated neural activity is transmitted to developing slow muscle cells, and synchronized activity spreads via gjd4/Cx46.8 GJ channels. Finally, we show that bioelectrical signal propagation within the developing neuromuscular system is required for appropriate myofiber organization and that disruption leads to defects in behavior. Our work reveals a molecular basis for GJ communication among developing muscle cells and reveals how perturbations to bioelectric signaling in the neuromuscular system may contribute to developmental myopathies. Moreover, this work underscores a critical motif of signal propagation between organ systems and highlights the pivotal role of GJ communication in coordinating bioelectric signaling during development.
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Affiliation(s)
| | - Judith S Eisen
- University of Oregon, Institute of Neuroscience, Eugene, OR 97405, USA
| | - Adam C Miller
- University of Oregon, Institute of Neuroscience, Eugene, OR 97405, USA.
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Lukowicz-Bedford RM, Eisen JS, Miller AC. Gap junction mediated bioelectric coordination is required for slow muscle development, organization, and function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.20.572619. [PMID: 38187655 PMCID: PMC10769300 DOI: 10.1101/2023.12.20.572619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Bioelectrical signaling, intercellular communication facilitated by membrane potential and electrochemical coupling, is emerging as a key regulator of animal development. Gap junction (GJ) channels can mediate bioelectric signaling by creating a fast, direct pathway between cells for the movement of ions and other small molecules. In vertebrates, GJ channels are formed by a highly conserved transmembrane protein family called the Connexins. The connexin gene family is large and complex, presenting a challenge in identifying the specific Connexins that create channels within developing and mature tissues. Using the embryonic zebrafish neuromuscular system as a model, we identify a connexin conserved across vertebrate lineages, gjd4, which encodes the Cx46.8 protein, that mediates bioelectric signaling required for appropriate slow muscle development and function. Through a combination of mutant analysis and in vivo imaging we show that gjd4/Cx46.8 creates GJ channels specifically in developing slow muscle cells. Using genetics, pharmacology, and calcium imaging we find that spinal cord generated neural activity is transmitted to developing slow muscle cells and synchronized activity spreads via gjd4/Cx46.8 GJ channels. Finally, we show that bioelectrical signal propagation within the developing neuromuscular system is required for appropriate myofiber organization, and that disruption leads to defects in behavior. Our work reveals the molecular basis for GJ communication among developing muscle cells and reveals how perturbations to bioelectric signaling in the neuromuscular system_may contribute to developmental myopathies. Moreover, this work underscores a critical motif of signal propagation between organ systems and highlights the pivotal role played by GJ communication in coordinating bioelectric signaling during development.
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Posukh OL, Maslova EA, Danilchenko VY, Zytsar MV, Orishchenko KE. Functional Consequences of Pathogenic Variants of the GJB2 Gene (Cx26) Localized in Different Cx26 Domains. Biomolecules 2023; 13:1521. [PMID: 37892203 PMCID: PMC10604905 DOI: 10.3390/biom13101521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 10/08/2023] [Accepted: 10/10/2023] [Indexed: 10/29/2023] Open
Abstract
One of the most common forms of genetic deafness has been predominantly associated with pathogenic variants in the GJB2 gene, encoding transmembrane protein connexin 26 (Cx26). The Cx26 molecule consists of an N-terminal domain (NT), four transmembrane domains (TM1-TM4), two extracellular loops (EL1 and EL2), a cytoplasmic loop, and a C-terminus (CT). Pathogenic variants in the GJB2 gene, resulting in amino acid substitutions scattered across the Cx26 domains, lead to a variety of clinical outcomes, including the most common non-syndromic autosomal recessive deafness (DFNB1A), autosomal dominant deafness (DFNA3A), as well as syndromic forms combining hearing loss and skin disorders. However, for rare and poorly documented variants, information on the mode of inheritance is often lacking. Numerous in vitro studies have been conducted to elucidate the functional consequences of pathogenic GJB2 variants leading to amino acid substitutions in different domains of Cx26 protein. In this work, we summarized all available data on a mode of inheritance of pathogenic GJB2 variants leading to amino acid substitutions and reviewed published information on their functional effects, with an emphasis on their localization in certain Cx26 domains.
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Affiliation(s)
- Olga L. Posukh
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Ekaterina A. Maslova
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Valeriia Yu. Danilchenko
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
| | - Marina V. Zytsar
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
| | - Konstantin E. Orishchenko
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia; (E.A.M.); (V.Y.D.); (M.V.Z.); (K.E.O.)
- Novosibirsk State University, 630090 Novosibirsk, Russia
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Baracaldo-Santamaría D, Corrales-Hernández MG, Ortiz-Vergara MC, Cormane-Alfaro V, Luque-Bernal RM, Calderon-Ospina CA, Cediel-Becerra JF. Connexins and Pannexins: Important Players in Neurodevelopment, Neurological Diseases, and Potential Therapeutics. Biomedicines 2022; 10:2237. [PMID: 36140338 PMCID: PMC9496069 DOI: 10.3390/biomedicines10092237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 08/30/2022] [Accepted: 09/01/2022] [Indexed: 11/16/2022] Open
Abstract
Cell-to-cell communication is essential for proper embryonic development and its dysfunction may lead to disease. Recent research has drawn attention to a new group of molecules called connexins (Cxs) and pannexins (Panxs). Cxs have been described for more than forty years as pivotal regulators of embryogenesis; however, the exact mechanism by which they provide this regulation has not been clearly elucidated. Consequently, Cxs and Panxs have been linked to congenital neurodegenerative diseases such as Charcot-Marie-Tooth disease and, more recently, chronic hemichannel opening has been associated with adult neurodegenerative diseases (e.g., Alzheimer's disease). Cell-to-cell communication via gap junctions formed by hexameric assemblies of Cxs, known as connexons, is believed to be a crucial component in developmental regulation. As for Panxs, despite being topologically similar to Cxs, they predominantly seem to form channels connecting the cytoplasm to the extracellular space and, despite recent research into Panx1 (Pannexin 1) expression in different regions of the brain during the embryonic phase, it has been studied to a lesser degree. When it comes to the nervous system, Cxs and Panxs play an important role in early stages of neuronal development with a wide span of action ranging from cellular migration during early stages to neuronal differentiation and system circuitry formation. In this review, we describe the most recent available evidence regarding the molecular and structural aspects of Cx and Panx channels, their role in neurodevelopment, congenital and adult neurological diseases, and finally propose how pharmacological modulation of these channels could modify the pathogenesis of some diseases.
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Affiliation(s)
- Daniela Baracaldo-Santamaría
- Pharmacology Unit, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
| | - María Gabriela Corrales-Hernández
- Pharmacology Unit, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
| | - Maria Camila Ortiz-Vergara
- Pharmacology Unit, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
| | - Valeria Cormane-Alfaro
- Pharmacology Unit, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
| | - Ricardo-Miguel Luque-Bernal
- Anatomy and Embriology Units, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
| | - Carlos-Alberto Calderon-Ospina
- Pharmacology Unit, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
- GENIUROS Research Group, Center for Research in Genetics and Genomics (CIGGUR), School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
| | - Juan-Fernando Cediel-Becerra
- Histology and Embryology Unit, Department of Biomedical Sciences, School of Medicine and Health Sciences, Universidad del Rosario, Bogotá 111221, Colombia
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