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Genetic compensation in a stable slc25a46 mutant zebrafish: A case for using F0 CRISPR mutagenesis to study phenotypes caused by inherited disease. PLoS One 2020; 15:e0230566. [PMID: 32208444 PMCID: PMC7092968 DOI: 10.1371/journal.pone.0230566] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Accepted: 03/03/2020] [Indexed: 12/22/2022] Open
Abstract
A phenomenon of genetic compensation is commonly observed when an organism with a disease-bearing mutation shows incomplete penetrance of the disease phenotype. Such incomplete phenotypic penetrance, or genetic compensation, is more commonly found in stable knockout models, rather than transient knockdown models. As such, these incidents present a challenge for the disease modeling field, although a deeper understanding of genetic compensation may also hold the key for novel therapeutic interventions. In our study we created a knockout model of slc25a46 gene, which is a recently discovered important player in mitochondrial dynamics, and deleterious mutations in which are known to cause peripheral neuropathy, optic atrophy and cerebellar ataxia. We report a case of genetic compensation in a stable slc25a46 homozygous zebrafish mutant (hereafter referred as “mutant”), in contrast to a penetrant disease phenotype in the first generation (F0) slc25a46 mosaic mutant (hereafter referred as “crispant”), generated with CRISPR/Cas-9 technology. We show that the crispant phenotype is specific and rescuable. By performing mRNA sequencing, we define significant changes in slc25a46 mutant’s gene expression profile, which are largely absent in crispants. We find that among the most significantly altered mRNAs, anxa6 gene stands out as a functionally relevant player in mitochondrial dynamics. We also find that our genetic compensation case does not arise from mechanisms driven by mutant mRNA decay. Our study contributes to the growing evidence of the genetic compensation phenomenon and presents novel insights about Slc25a46 function. Furthermore, our study provides the evidence for the efficiency of F0 CRISPR screens for disease candidate genes, which may be used to advance the field of functional genetics.
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Investigation of Islet2a function in zebrafish embryos: Mutants and morphants differ in morphologic phenotypes and gene expression. PLoS One 2018; 13:e0199233. [PMID: 29927984 PMCID: PMC6013100 DOI: 10.1371/journal.pone.0199233] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2017] [Accepted: 06/04/2018] [Indexed: 12/19/2022] Open
Abstract
Zebrafish primary motor neurons differ from each other with respect to morphology, muscle targets and electrophysiological properties. For example, CaP has 2-3-fold larger densities of both inward and outward currents than do other motor neurons. We tested whether the transcription factor Islet2a, uniquely expressed in CaP, but not other primary motor neurons, plays a role in specifying its stereotypic electrophysiological properties. We used both TALEN-based gene editing and antisense morpholino approaches to disrupt Islet2a function. Our electrophysiology results do not support a specific role for Islet2a in determining CaP’s unique electrical properties. However, we also found that the morphological phenotypes of CaP and a later-born motor neuron differed between islet2a mutants and morphants. Using microarrays, we tested whether the gene expression profiles of whole embryo morphants, mutants and controls also differed. Morphants had 174 and 201 genes that were differentially expressed compared to mutants and controls, respectively. Further, islet2a was identified as a differentially expressed gene. To examine how mutation of islet2a affected islet gene expression specifically in CaPs, we performed RNA in situ hybridization. We detected no obvious differences in expression of islet1, islet2a, or islet2b in CaPs of mutant versus sibling control embryos. However, immunolabeling studies revealed that an Islet protein persisted in CaPs of mutants, albeit at a reduced level compared to controls. While we cannot exclude requirement for some Islet protein, we conclude that differentiation of the CaP’s stereotypic large inward and outward currents does not have a specific requirement for Islet2a.
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3
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Livin' On The Edge: glia shape nervous system transition zones. Curr Opin Neurobiol 2017; 47:44-51. [PMID: 28957729 DOI: 10.1016/j.conb.2017.09.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 09/11/2017] [Indexed: 11/21/2022]
Abstract
The vertebrate nervous system is divided into two functional halves; the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which consists of nerves and ganglia. Incoming peripheral stimuli transmitted from the periphery to the CNS and subsequent motor responses created because of this information, require efficient communication between the two halves that make up this organ system. Neurons and glial cells of each half of the nervous system, which are the main actors in this communication, segregate across nervous system transition zones and never mix, allowing for efficient neurotransmission. Studies aimed at understanding the cellular and molecular mechanisms governing the development and maintenance of these transition zones have predominantly focused on mammalian models. However, zebrafish has emerged as a powerful model organism to study these structures and has allowed researchers to identify novel glial cells and mechanisms essential for nervous system assembly. This review will highlight recent advances into the important role that glial cells play in building and maintaining the nervous system and its boundaries.
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Myosin phosphatase Fine-tunes Zebrafish Motoneuron Position during Axonogenesis. PLoS Genet 2016; 12:e1006440. [PMID: 27855159 PMCID: PMC5147773 DOI: 10.1371/journal.pgen.1006440] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Accepted: 10/21/2016] [Indexed: 01/30/2023] Open
Abstract
During embryogenesis the spinal cord shifts position along the anterior-posterior axis relative to adjacent tissues. How motor neurons whose cell bodies are located in the spinal cord while their axons reside in adjacent tissues compensate for such tissue shift is not well understood. Using live cell imaging in zebrafish, we show that as motor axons exit from the spinal cord and extend through extracellular matrix produced by adjacent notochord cells, these cells shift several cell diameters caudally. Despite this pronounced shift, individual motoneuron cell bodies stay aligned with their extending axons. We find that this alignment requires myosin phosphatase activity within motoneurons, and that mutations in the myosin phosphatase subunit mypt1 increase myosin phosphorylation causing a displacement between motoneuron cell bodies and their axons. Thus, we demonstrate that spinal motoneurons fine-tune their position during axonogenesis and we identify the myosin II regulatory network as a key regulator.
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Seredick S, Hutchinson SA, Van Ryswyk L, Talbot JC, Eisen JS. Lhx3 and Lhx4 suppress Kolmer-Agduhr interneuron characteristics within zebrafish axial motoneurons. Development 2014; 141:3900-9. [PMID: 25231761 DOI: 10.1242/dev.105718] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A central problem in development is how fates of closely related cells are segregated. Lineally related motoneurons (MNs) and interneurons (INs) express many genes in common yet acquire distinct fates. For example, in mouse and chick Lhx3 plays a pivotal role in the development of both cell classes. Here, we utilize the ability to recognize individual zebrafish neurons to examine the roles of Lhx3 and its paralog Lhx4 in the development of MNs and ventral INs. We show that Lhx3 and Lhx4 are expressed by post-mitotic axial MNs derived from the MN progenitor (pMN) domain, p2 domain progenitors and by several types of INs derived from pMN and p2 domains. In the absence of Lhx3 and Lhx4, early-developing primary MNs (PMNs) adopt a hybrid fate, with morphological and molecular features of both PMNs and pMN-derived Kolmer-Agduhr' (KA') INs. In addition, we show that Lhx3 and Lhx4 distinguish the fates of two pMN-derived INs. Finally, we demonstrate that Lhx3 and Lhx4 are necessary for the formation of late-developing V2a and V2b INs. In conjunction with our previous work, these data reveal that distinct transcription factor families are deployed in post-mitotic MNs to unequivocally assign MN fate and suppress the development of alternative pMN-derived IN fates.
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Affiliation(s)
- Steve Seredick
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA
| | - Sarah A Hutchinson
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA
| | - Liesl Van Ryswyk
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA
| | - Jared C Talbot
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA
| | - Judith S Eisen
- Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA
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Carlisle TC, Ribera AB. Connexin 35b expression in the spinal cord of Danio rerio embryos and larvae. J Comp Neurol 2014; 522:861-75. [PMID: 23939687 DOI: 10.1002/cne.23449] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 07/10/2013] [Accepted: 08/02/2013] [Indexed: 11/11/2022]
Abstract
Electrical synapses are expressed prominently in the developing and mature nervous systems. Unlike chemical synapses, little is known about the developmental role of electrical synapses, reflecting the limitations imposed by the lack of selective pharmacological blockers. At a molecular level, the building blocks of electrical synapses are connexin proteins. In this study, we report the expression pattern for neuronally expressed connexin 35b (cx35b), the zebrafish orthologue of mammalian connexin (Cx) 36. We find that cx35b is expressed at the time of neural induction, indicating a possible early role in neural progenitor cells. Additionally, cx35b localizes to the ventral spinal cord during embryonic and early larval stages. We detect cx35b mRNA in secondary motor neurons (SMNs) and interneurons. We identified the premotor circumferential descending (CiD) interneuron as one interneuron subtype expressing cx35b. In addition, cx35b is present in other ventral interneurons of unknown subtype(s). This early expression of cx35b in SMNs and CiDs suggests a possible role in motor network function during embryonic and larval stages.
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Affiliation(s)
- Tara C Carlisle
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, 80045; Neuroscience Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado, 80045; Colorado Clinical and Translational Sciences Institute, University of Colorado Anschutz Medical Campus, Aurora, Colorado, 80045; Medical Scientist Training Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado, 80045
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7
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The role of inab in axon morphology of an identified zebrafish motoneuron. PLoS One 2014; 9:e88631. [PMID: 24533123 PMCID: PMC3922942 DOI: 10.1371/journal.pone.0088631] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 01/15/2014] [Indexed: 12/15/2022] Open
Abstract
The ability of an animal to move and to interact with its environment requires that motoneurons correctly innervate specific muscles. Although many genes that regulate motoneuron development have been identified, our understanding of motor axon branching remains incomplete. We used transcriptional expression profiling to identify potential candidate genes involved in development of zebrafish identified motoneurons. Here we focus on inab, an intermediate filament encoding gene dynamically expressed in a subset of motoneurons as well as in an identified interneuron. We show that inab is necessary for proper axon morphology of a specific motoneuron subtype.
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Morimura R, Nozawa K, Tanaka H, Ohshima T. Phosphorylation of Dpsyl2 (CRMP2) and Dpsyl3 (CRMP4) is required for positioning of caudal primary motor neurons in the zebrafish spinal cord. Dev Neurobiol 2013; 73:911-20. [DOI: 10.1002/dneu.22117] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 07/23/2013] [Accepted: 07/28/2013] [Indexed: 11/11/2022]
Affiliation(s)
- Rii Morimura
- Department of Life Science and Medical Bioscience; Waseda University; 2-2 Wakamatsu-cho, Shinjuku-ku Tokyo 162-8480 Japan
| | - Keisuke Nozawa
- Department of Life Science and Medical Bioscience; Waseda University; 2-2 Wakamatsu-cho, Shinjuku-ku Tokyo 162-8480 Japan
| | - Hideomi Tanaka
- Department of Life Science and Medical Bioscience; Waseda University; 2-2 Wakamatsu-cho, Shinjuku-ku Tokyo 162-8480 Japan
- Laboratory for Developmental Gene Regulation; RIKEN Brain Science Institute (BSI); 2-1 Hirosawa, Wako Saitama 351-0198 Japan
| | - Toshio Ohshima
- Department of Life Science and Medical Bioscience; Waseda University; 2-2 Wakamatsu-cho, Shinjuku-ku Tokyo 162-8480 Japan
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Seredick SD, Van Ryswyk L, Hutchinson SA, Eisen JS. Zebrafish Mnx proteins specify one motoneuron subtype and suppress acquisition of interneuron characteristics. Neural Dev 2012; 7:35. [PMID: 23122226 PMCID: PMC3570319 DOI: 10.1186/1749-8104-7-35] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Accepted: 10/16/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Precise matching between motoneuron subtypes and the muscles they innervate is a prerequisite for normal behavior. Motoneuron subtype identity is specified by the combination of transcription factors expressed by the cell during its differentiation. Here we investigate the roles of Mnx family transcription factors in specifying the subtypes of individually identified zebrafish primary motoneurons. RESULTS Zebrafish has three Mnx family members. We show that each of them has a distinct and temporally dynamic expression pattern in each primary motoneuron subtype. We also show that two Mnx family members are expressed in identified VeLD interneurons derived from the same progenitor domain that generates primary motoneurons. Surprisingly, we found that Mnx proteins appear unnecessary for differentiation of VeLD interneurons or the CaP motoneuron subtype. Mnx proteins are, however, required for differentiation of the MiP motoneuron subtype. We previously showed that MiPs require two temporally-distinct phases of Islet1 expression for normal development. Here we show that in the absence of Mnx proteins, the later phase of Islet1 expression is initiated but not sustained, and MiPs become hybrids that co-express morphological and molecular features of motoneurons and V2a interneurons. Unexpectedly, these hybrid MiPs often extend CaP-like axons, and some MiPs appear to be entirely transformed to a CaP morphology. CONCLUSIONS Our results suggest that Mnx proteins promote MiP subtype identity by suppressing both interneuron development and CaP axon pathfinding. This is, to our knowledge, the first report of transcription factors that act to distinguish CaP and MiP subtype identities. Our results also suggest that MiP motoneurons are more similar to V2 interneurons than are CaP motoneurons.
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Affiliation(s)
- Steve D Seredick
- Institute of Neuroscience, University of Oregon, Eugene, OR, USA
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Umeda K, Shoji W, Sakai S, Muto A, Kawakami K, Ishizuka T, Yawo H. Targeted expression of a chimeric channelrhodopsin in zebrafish under regulation of Gal4-UAS system. Neurosci Res 2012; 75:69-75. [PMID: 23044184 DOI: 10.1016/j.neures.2012.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Revised: 08/09/2012] [Accepted: 08/20/2012] [Indexed: 10/27/2022]
Abstract
Channelrhodopsin (ChR)-wide receiver (ChRWR), one of the chimeric molecule of ChR1 and ChR2, has several advantages over ChR2 such as improved expression in the plasma membrane and enhanced photocurrent with small desensitization. Here we generated transgenic zebrafish (Danio rerio) expressing ChRWR as a conjugate of EGFP under the regulation of UAS promoter (UAS:ChRWR-EGFP). When crossed with a Gal4 line, SAGFF36B, ChRWR-EGFP was selectively expressed in primary mechanosensory Rohon-Beard (RB) neurons. The direct photoactivation of RB neurons was sufficient to trigger the escape behavior. The UAS:ChRWR-EGFP line could facilitate a variety of investigations of neural networks and behaviors of zebrafish in vivo.
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Affiliation(s)
- Keiko Umeda
- Department of Developmental Biology & Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Japan
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Chondrolectin mediates growth cone interactions of motor axons with an intermediate target. J Neurosci 2012; 32:4426-39. [PMID: 22457492 DOI: 10.1523/jneurosci.5179-11.2012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The C-type lectin chondrolectin (chodl) represents one of the major gene products dysregulated in spinal muscular atrophy models in mice. However, to date, no function has been determined for the gene. We have identified chodl and other novel genes potentially involved in motor axon differentiation, by expression profiling of transgenically labeled motor neurons in embryonic zebrafish. To enrich the profile for genes involved in differentiation of peripheral motor axons, we inhibited the function of LIM-HDs (LIM homeodomain factors) by overexpression of a dominant-negative cofactor, thereby rendering labeled axons unable to grow out of the spinal cord. Importantly, labeled cells still exhibited axon growth and most cells retained markers of motor neuron identity. Functional tests of chodl, by overexpression and knockdown, confirm crucial functions of this gene for motor axon growth in vivo. Indeed, knockdown of chodl induces arrest or stalling of motor axon growth at the horizontal myoseptum, an intermediate target and navigational choice point, and reduced muscle innervation at later developmental stages. This phenotype is rescued by chodl overexpression, suggesting that correct expression levels of chodl are important for interactions of growth cones of motor axons with the horizontal myoseptum. Combined, these results identify upstream regulators and downstream functions of chodl during motor axon growth.
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Crossing the border: molecular control of motor axon exit. Int J Mol Sci 2011; 12:8539-61. [PMID: 22272090 PMCID: PMC3257087 DOI: 10.3390/ijms12128539] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Revised: 11/05/2011] [Accepted: 11/08/2011] [Indexed: 11/23/2022] Open
Abstract
Living organisms heavily rely on the function of motor circuits for their survival and for adapting to ever-changing environments. Unique among central nervous system (CNS) neurons, motor neurons (MNs) project their axons out of the CNS. Once in the periphery, motor axons navigate along highly stereotyped trajectories, often at considerable distances from their cell bodies, to innervate appropriate muscle targets. A key decision made by pathfinding motor axons is whether to exit the CNS through dorsal or ventral motor exit points (MEPs). In contrast to the major advances made in understanding the mechanisms that regulate the specification of MN subtypes and the innervation of limb muscles, remarkably little is known about how MN axons project out of the CNS. Nevertheless, a limited number of studies, mainly in Drosophila, have identified transcription factors, and in some cases candidate downstream effector molecules, that are required for motor axons to exit the spinal cord. Notably, specialized neural crest cell derivatives, referred to as Boundary Cap (BC) cells, pre-figure and demarcate MEPs in vertebrates. Surprisingly, however, BC cells are not required for MN axon exit, but rather restrict MN cell bodies from ectopically migrating along their axons out of the CNS. Here, we describe the small set of studies that have addressed motor axon exit in Drosophila and vertebrates, and discuss our fragmentary knowledge of the mechanisms, which guide motor axons out of the CNS.
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Hale LA, Fowler DK, Eisen JS. Netrin signaling breaks the equivalence between two identified zebrafish motoneurons revealing a new role of intermediate targets. PLoS One 2011; 6:e25841. [PMID: 22003409 PMCID: PMC3189217 DOI: 10.1371/journal.pone.0025841] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 09/12/2011] [Indexed: 12/11/2022] Open
Abstract
Background We previously showed that equivalence between two identified zebrafish motoneurons is broken by interactions with identified muscle fibers that act as an intermediate target for the axons of these motoneurons. Here we investigate the molecular basis of the signaling interaction between the intermediate target and the motoneurons. Principal Findings We provide evidence that Netrin 1a is an intermediate target-derived signal that causes two equivalent motoneurons to adopt distinct fates. We show that although these two motoneurons express the same Netrin receptors, their axons respond differently to Netrin 1a encountered at the intermediate target. Furthermore, we demonstrate that when Netrin 1a is knocked down, more distal intermediate targets that express other Netrins can also function to break equivalence between these motoneurons. Significance Our results suggest a new role for intermediate targets in breaking neuronal equivalence. The data we present reveal that signals encountered during axon pathfinding can cause equivalent neurons to adopt distinct fates. Such signals may be key in diversifying a neuronal population and leading to correct circuit formation.
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Affiliation(s)
- Laura A. Hale
- Institute of Neuroscience, University of Oregon, Eugene, Oregon, United States of America
| | - Daniel K. Fowler
- Institute of Neuroscience, University of Oregon, Eugene, Oregon, United States of America
| | - Judith S. Eisen
- Institute of Neuroscience, University of Oregon, Eugene, Oregon, United States of America
- * E-mail:
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Genetic visualization with an improved GCaMP calcium indicator reveals spatiotemporal activation of the spinal motor neurons in zebrafish. Proc Natl Acad Sci U S A 2011; 108:5425-30. [PMID: 21383146 DOI: 10.1073/pnas.1000887108] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Animal behaviors are generated by well-coordinated activation of neural circuits. In zebrafish, embryos start to show spontaneous muscle contractions at 17 to 19 h postfertilization. To visualize how motor circuits in the spinal cord are activated during this behavior, we developed GCaMP-HS (GCaMP-hyper sensitive), an improved version of the genetically encoded calcium indicator GCaMP, and created transgenic zebrafish carrying the GCaMP-HS gene downstream of the Gal4-recognition sequence, UAS (upstream activation sequence). Then we performed a gene-trap screen and identified the SAIGFF213A transgenic fish that expressed Gal4FF, a modified version of Gal4, in a subset of spinal neurons including the caudal primary (CaP) motor neurons. We conducted calcium imaging using the SAIGFF213A; UAS:GCaMP-HS double transgenic embryos during the spontaneous contractions. We demonstrated periodic and synchronized activation of a set of ipsilateral motor neurons located on the right and left trunk in accordance with actual muscle movements. The synchronized activation of contralateral motor neurons occurred alternately with a regular interval. Furthermore, a detailed analysis revealed rostral-to-caudal propagation of activation of the ipsilateral motor neuron, which is similar to but much slower than the rostrocaudal delay observed during swimming in later stages. Our study thus demonstrated coordinated activities of the motor neurons during the first behavior in a vertebrate. We propose the GCaMP technology combined with the Gal4FF-UAS system is a powerful tool to study functional neural circuits in zebrafish.
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Abstract
For more than a decade, the zebrafish has proven to be an excellent model organism to investigate the mechanisms of neurogenesis during development. The often cited advantages, namely external development, genetic, and optical accessibility, have permitted direct examination and experimental manipulations of neurogenesis during development. Recent studies have begun to investigate adult neurogenesis, taking advantage of its widespread occurrence in the mature zebrafish brain to investigate the mechanisms underlying neural stem cell maintenance and recruitment. Here we provide a comprehensive overview of the tools and techniques available to study neurogenesis in zebrafish both during development and in adulthood. As useful resources, we provide tables of available molecular markers, transgenic, and mutant lines. We further provide optimized protocols for studying neurogenesis in the adult zebrafish brain, including in situ hybridization, immunohistochemistry, in vivo lipofection and electroporation methods to deliver expression constructs, administration of bromodeoxyuridine (BrdU), and finally slice cultures. These currently available tools have put zebrafish on par with other model organisms used to investigate neurogenesis.
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Affiliation(s)
- Prisca Chapouton
- Institute of Developmental Genetics, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
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Kucenas S, Wang WD, Knapik EW, Appel B. A selective glial barrier at motor axon exit points prevents oligodendrocyte migration from the spinal cord. J Neurosci 2009; 29:15187-94. [PMID: 19955371 PMCID: PMC2837368 DOI: 10.1523/jneurosci.4193-09.2009] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2009] [Revised: 10/09/2009] [Accepted: 10/19/2009] [Indexed: 11/21/2022] Open
Abstract
Nerve roots have specialized transition zones that permit axon extension but limit cell movement between the CNS and PNS. Boundary cap cells prevent motor neuron soma from following their axons into the periphery, thereby contributing to a selective barrier. Transition zones also restrict movement of glial cells. Consequently, axons that cross the CNS-PNS interface are insulated by central and peripheral myelin. The mechanisms that prevent the migratory progenitors of oligodendrocytes and Schwann cells, the myelinating cells of the CNS and PNS, respectively, from crossing transition zones are not known. Here, we show that interactions between myelinating glial cells prevent their movements across the interface. Using in vivo time-lapse imaging in zebrafish we found that, in the absence of Schwann cells, oligodendrocyte progenitors cross ventral root transition zones and myelinate motor axons. These studies reveal that distinct mechanisms regulate the movement of axons, neurons, and glial cells across the CNS-PNS interface.
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Affiliation(s)
- Sarah Kucenas
- Department of Biological Sciences
- Vanderbilt Program in Developmental Biology, and
| | - Wen-Der Wang
- Vanderbilt Program in Developmental Biology, and
- Division of Genetic Medicine, Vanderbilt University, Nashville, Tennessee, 37235, and
| | - Ela W. Knapik
- Vanderbilt Program in Developmental Biology, and
- Division of Genetic Medicine, Vanderbilt University, Nashville, Tennessee, 37235, and
| | - Bruce Appel
- Department of Biological Sciences
- Department of Pediatrics, University of Colorado Denver–Anschutz Medical Campus, Aurora, Colorado 80045
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Schmidt ER, Pasterkamp RJ, van den Berg LH. Axon guidance proteins: Novel therapeutic targets for ALS? Prog Neurobiol 2009; 88:286-301. [DOI: 10.1016/j.pneurobio.2009.05.004] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2008] [Revised: 04/06/2009] [Accepted: 05/27/2009] [Indexed: 12/12/2022]
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Hilario JD, Rodino-Klapac LR, Wang C, Beattie CE. Semaphorin 5A is a bifunctional axon guidance cue for axial motoneurons in vivo. Dev Biol 2008; 326:190-200. [PMID: 19059233 DOI: 10.1016/j.ydbio.2008.11.007] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Revised: 11/07/2008] [Accepted: 11/10/2008] [Indexed: 10/21/2022]
Abstract
Semaphorins are a large class of proteins that function throughout the nervous system to guide axons. It had previously been shown that Semaphorin 5A (Sema5A) was a bifunctional axon guidance cue for mammalian midbrain neurons. We found that zebrafish sema5A was expressed in myotomes during the period of motor axon outgrowth. To determine whether Sema5A functioned in motor axon guidance, we knocked down Sema5A, which resulted in two phenotypes: a delay in motor axon extension into the ventral myotome and aberrant branching of these motor axons. Both phenotypes were rescued by injection of full-length rat Sema5A mRNA. However, adding back RNA encoding the sema domain alone significantly rescued the branching phenotype in sema5A morphants. Conversely, adding back RNA encoding the thrombospondin repeat (TSR) domain alone into sema5A morphants exclusively rescued delay in ventral motor axon extension. Together, these data show that Sema5A is a bifunctional axon guidance cue for vertebrate motor axons in vivo. The TSR domain promotes growth of developing motor axons into the ventral myotome whereas the sema domain mediates repulsion and keeps these motor axons from branching into surrounding myotome regions.
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Affiliation(s)
- Jona D Hilario
- Center for Molecular Neurobiology and Department of Neuroscience, The Ohio State University, 190 Rightmire Hall, 1060 Carmack Rd, Columbus, OH 43210, USA
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Abstract
The heat shock promoter is useful for regulating transgene expression in small water-living organisms. In zebrafish embryos, downstream gene expression can be greatly induced throughout the body by raising the temperature from 28.5 degrees C to 38.0 degrees C. By manipulating the local temperature within an embryo, spatial control of transgene expression is also possible. One such way for inducing heat shock response in targeted cells is by using a laser microbeam under the microscope. In addition, random mosaic expression by transient gene expression and transplantation of the transgenic embryo into a wild type host can be considered a powerful tool for studying gene functions using this promoter. In this paper, we review the applications of the zebrafish heat shock protein promoter as a gene expression tool and for lineage labeling and transcription enhancer screening.
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Affiliation(s)
- Wataru Shoji
- Department of Cell Biology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
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