Publications by authors named "Joel C Glover"

67 Publications

Transcriptome analysis reveals disparate expression of inflammation-related miRNAs and their gene targets in iPSC-astrocytes from people with schizophrenia.

Brain Behav Immun 2021 05 9;94:235-244. Epub 2021 Feb 9.

NORMENT, Institute of Clinical Medicine, University of Oslo, and Division of Mental Health and Addiction, Oslo University Hospital, Oslo, Norway; Department of Medical Genetics, Oslo University Hospital, Oslo, Norway. Electronic address:

Despite the high heritability of schizophrenia (SCZ), details of its pathophysiology and etiology are still unknown. Recent findings suggest that aberrant inflammatory regulation and microRNAs (miRNAs) are involved. Here we performed a comparative analysis of the global miRNome of human induced pluripotent stem cell (iPSC)-astrocytes, derived from SCZ patients and healthy controls (CTRLs), at baseline and following inflammatory modulation using IL-1β. We identified four differentially expressed miRNAs (miR-337-3p, miR-127-5p, miR-206, miR-1185-1-3p) in SCZ astrocytes that exhibited significantly lower baseline expression relative to CTRLs. Group-specific differential expression (DE) analyses exploring possible distinctions in the modulatory capacity of IL-1β on miRNA expression in SCZ versus CTRL astroglia revealed trends toward altered miRNA expressions. In addition, we analyzed peripheral blood samples from a large cohort of SCZ patients (n = 484) and CTRLs (n = 496) screening for the expression of specific gene targets of the four DE miRNAs that were identified in our baseline astrocyte setup. Three of these genes, LAMTOR4, IL23R, and ERBB3, had a significantly lower expression in the blood of SCZ patients compared to CTRLs after multiple testing correction. We also found nominally significant differences for ERBB2 and IRAK1, which similarly displayed lower expressions in SCZ versus CTRL. Furthermore, we found matching patterns between the expressions of identified miRNAs and their target genes when comparing our in vitro and in vivo results. The current results further our understanding of the pathobiological basis of SCZ.
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http://dx.doi.org/10.1016/j.bbi.2021.01.037DOI Listing
May 2021

N-acetylcysteine amide ameliorates mitochondrial dysfunction and reduces oxidative stress in hiPSC-derived dopaminergic neurons with POLG mutation.

Exp Neurol 2021 Mar 29;337:113536. Epub 2020 Nov 29.

Neuro-SysMed, Center of Excellence for Clinical Research in Neurological Diseases, Department of Neurology, Haukeland University Hospital, Jonas Lies vei 87, P. O. Box 7804, 5021 Bergen, Norway; Department of Clinical Medicine (K1), University of Bergen, Jonas Lies vei 87, P. O. Box 7804, 5021 Bergen, Norway. Electronic address:

The inability to reliably replicate mitochondrial DNA (mtDNA) by mitochondrial DNA polymerase gamma (POLG) leads to a subset of common mitochondrial diseases associated with neuronal death and depletion of neuronal mtDNA. Defining disease mechanisms in neurons remains difficult due to the limited access to human tissue. Using human induced pluripotent stem cells (hiPSCs), we generated functional dopaminergic (DA) neurons showing positive expression of dopaminergic markers TH and DAT, mature neuronal marker MAP2 and functional synaptic markers synaptophysin and PSD-95. These DA neurons were electrophysiologically characterized, and exhibited inward Na + currents, overshooting action potentials and spontaneous postsynaptic currents (sPSCs). POLG patient-specific DA neurons (POLG-DA neurons) manifested a phenotype that replicated the molecular and biochemical changes found in patient post-mortem brain samples namely loss of complex I and depletion of mtDNA. Compared to disease-free hiPSC-derived DA neurons, POLG-DA neurons exhibited loss of mitochondrial membrane potential, loss of complex I and loss of mtDNA and TFAM expression. POLG driven mitochondrial dysfunction also led to neuronal ROS overproduction and increased cellular senescence. This deficit was selectively rescued by treatment with N-acetylcysteine amide (NACA). In conclusion, our study illustrates the promise of hiPSC technology for assessing pathogenetic mechanisms associated with POLG disease, and that NACA can be a promising potential therapy for mitochondrial diseases such as those caused by POLG mutation.
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http://dx.doi.org/10.1016/j.expneurol.2020.113536DOI Listing
March 2021

A versatile toolbox for semi-automatic cell-by-cell object-based colocalization analysis.

Sci Rep 2020 11 4;10(1):19027. Epub 2020 Nov 4.

Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, University of Oslo, Blindern, 1105, Oslo, Norway.

Differential fluorescence labeling and multi-fluorescence imaging followed by colocalization analysis is commonly used to investigate cellular heterogeneity in situ. This is particularly important when investigating the biology of tissues with diverse cell types. Object-based colocalization analysis (OBCA) tools can employ automatic approaches, which are sensitive to errors in cell segmentation, or manual approaches, which can be impractical and tedious. Here, we present a novel set of tools for OBCA using a semi-automatic approach, consisting of two ImageJ plugins, a Microsoft Excel macro, and a MATLAB script. One ImageJ plugin enables customizable processing of multichannel 3D images for enhanced visualization of features relevant to OBCA, and another enables semi-automatic colocalization quantification. The Excel macro and the MATLAB script enable data organization and 3D visualization of object data across image series. The tools are well suited for experiments involving complex and large image data sets, and can be used in combination or as individual components, allowing flexible, efficient and accurate OBCA. Here we demonstrate their utility in immunohistochemical analyses of the developing central nervous system, which is characterized by complexity in the number and distribution of cell types, and by high cell packing densities, which can both create challenging situations for OBCA.
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http://dx.doi.org/10.1038/s41598-020-75835-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7643144PMC
November 2020

Oikopleura.

Authors:
Joel C Glover

Curr Biol 2020 10;30(20):R1243-R1245

Sars International Center for Marine Molecular Biology, University of Bergen, Thormøhlens gate 15, Bergen, Norway; Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, University of Oslo, PB 1105 Blindern, Oslo, Norway. Electronic address:

The appendicularian tunicate Oikopleura epitomizes the degree to which evolution can constrain both genome and cellular composition, while at the same time unleashing fantastic specializations.
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http://dx.doi.org/10.1016/j.cub.2020.07.075DOI Listing
October 2020

Author Correction: Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits.

Sci Rep 2020 Aug 6;10(1):13531. Epub 2020 Aug 6.

Université catholique de Louvain, Institute of Neuroscience, Laboratory of Neural Differentiation, Brussels, Belgium.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41598-020-70339-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7414022PMC
August 2020

Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits.

Sci Rep 2020 01 22;10(1):996. Epub 2020 Jan 22.

Université catholique de Louvain, Institute of Neuroscience, Laboratory of Neural Differentiation, Brussels, Belgium.

In the developing spinal cord, Onecut transcription factors control the diversification of motor neurons into distinct neuronal subsets by ensuring the maintenance of Isl1 expression during differentiation. However, other genes downstream of the Onecut proteins and involved in motor neuron diversification have remained unidentified. In the present study, we generated conditional mutant embryos carrying specific inactivation of Onecut genes in the developing motor neurons, performed RNA-sequencing to identify factors downstream of Onecut proteins in this neuron population, and employed additional transgenic mouse models to assess the role of one specific Onecut-downstream target, the transcription factor Nkx6.2. Nkx6.2 expression was up-regulated in Onecut-deficient motor neurons, but strongly downregulated in Onecut-deficient V2a interneurons, indicating an opposite regulation of Nkx6.2 by Onecut factors in distinct spinal neuron populations. Nkx6.2-null embryos, neonates and adult mice exhibited alterations of locomotor pattern and spinal locomotor network activity, likely resulting from defective survival of a subset of limb-innervating motor neurons and abnormal migration of V2a interneurons. Taken together, our results indicate that Nkx6.2 regulates the development of spinal neuronal populations and the formation of the spinal locomotor circuits downstream of the Onecut transcription factors.
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http://dx.doi.org/10.1038/s41598-020-57945-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6976625PMC
January 2020

In vivo Cell Tracking Using Non-invasive Imaging of Iron Oxide-Based Particles with Particular Relevance for Stem Cell-Based Treatments of Neurological and Cardiac Disease.

Mol Imaging Biol 2020 12;22(6):1469-1488

Department of Medicine and Surgery, University of Parma, Parma, Italy.

Stem cell-based therapeutics is a rapidly developing field associated with a number of clinical challenges. One such challenge lies in the implementation of methods to track stem cells and stem cell-derived cells in experimental animal models and in the living patient. Here, we provide an overview of cell tracking in the context of cardiac and neurological disease, focusing on the use of iron oxide-based particles (IOPs) visualized in vivo using magnetic resonance imaging (MRI). We discuss the types of IOPs available for such tracking, their advantages and limitations, approaches for labeling cells with IOPs, biological interactions and effects of IOPs at the molecular and cellular levels, and MRI-based and associated approaches for in vivo and histological visualization. We conclude with reviews of the literature on IOP-based cell tracking in cardiac and neurological disease, covering both preclinical and clinical studies.
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http://dx.doi.org/10.1007/s11307-019-01440-4DOI Listing
December 2020

Loss of Tiparp Results in Aberrant Layering of the Cerebral Cortex.

eNeuro 2019 Nov/Dec;6(6). Epub 2019 Nov 27.

Institute of Basic Medical Sciences, University of Oslo, Oslo 0372, Norway

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP) is an enzyme that adds a single ADP-ribose moiety to itself or other proteins. Tiparp is highly expressed in the brain; however, its function in this organ is unknown. Here, we used mice to determine Tiparp's role in the development of the prefrontal cortex. Loss of Tiparp resulted in an aberrant organization of the mouse cortex, where the upper layers presented increased cell density in the knock-out mice compared with wild type. Tiparp loss predominantly affected the correct distribution and number of GABAergic neurons. Furthermore, neural progenitor cell proliferation was significantly reduced. Neural stem cells (NSCs) derived from mice showed a slower rate of migration. Cytoskeletal components, such as α-tubulin are key regulators of neuronal differentiation and cortical development. α-tubulin mono-ADP ribosylation (MAR) levels were reduced in cells, suggesting that Tiparp plays a role in the MAR of α-tubulin. Despite the mild phenotype presented by mice, our findings reveal an important function for Tiparp and MAR in the correct development of the cortex. Unravelling Tiparp's role in the cortex, could pave the way to a better understanding of a wide spectrum of neurological diseases which are known to have increased expression of .
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http://dx.doi.org/10.1523/ENEURO.0239-19.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6883171PMC
June 2020

Gap junction-dependent coordination of intercellular calcium signalling in the developing appendicularian tunicate Oikopleura dioica.

Dev Biol 2019 06 21;450(1):9-22. Epub 2019 Mar 21.

Sars International Centre for Marine Molecular Biology, University of Bergen, Norway; Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway. Electronic address:

We characterized spontaneous Ca2+ signals in Oikopleura dioica embryos from pre-fertilization to gastrula stages following injection of GCaMP6 mRNA into unfertilized eggs. The unfertilized egg exhibited regular, transient elevations in intracellular Ca2+ concentration with an average duration of 4-6 s and an average frequency of about 1 every 2.5 min. Fertilization was accompanied by a longer Ca2+ transient that lasted several minutes. Thereafter, regular Ca2+ transients were reinstated that spread within seconds among blastomeres and gradually increased in duration (by about 50%) and decreased in frequency (by about 20%) by gastrulation. Peak amplitudes also exhibited a dynamic, with a transitory drop occurring at about the 4-cell stage and a subsequent rise. Each peak was preceded by about 15 s by a smaller and shorter Ca2+ increase (about 5% of the main peak amplitude, average duration 3 s), which we term the "minipeak". By gastrulation, Ca2+ transients exhibited a stereotyped initiation site on either side of the 32-64-cell embryo, likely in the nascent muscle precursor cells, and spread thereafter symmetrically in a stereotyped spatial pattern that engaged blastomeres giving rise to all the major tissue lineages. The rapid spread of the transients relative to the intertransient interval created a coordinated wave that, on a coarse time scale, could be considered an approximate synchronization. Treatment with the divalent cations Ni2+ or Cd2+ gradually diminished peak amplitudes, had only moderate effects on wave frequency, but markedly disrupted wave synchronization and normal development. The T-type Ca2+ channel blocker mibefradil similarly disrupted normal development, and eliminated the minipeaks, but did not affect wave synchronization. To assess the role of gap junctions in calcium wave spread and coordination, we first characterized the expression of two Oikopleura connexins, Od-CxA and Od-CxB, both of which are expressed during pre-gastrulation and gastrula stages, and then co-injected double-stranded inhibitory RNAs together with CGaMP6 to suppress connexin expression. Connexin mRNA knockdown led to a gradual increase in Ca2+ transient peak width, a decrease of interpeak interval and a marked disruption of wave synchronization. As seen with divalent cations and mibefradil, this desynchronization was accompanied by a disruption of normal development.
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http://dx.doi.org/10.1016/j.ydbio.2019.03.006DOI Listing
June 2019

Molecular Profiling Defines Evolutionarily Conserved Transcription Factor Signatures of Major Vestibulospinal Neuron Groups.

eNeuro 2019 Jan-Feb;6(1). Epub 2019 Feb 27.

Department of Molecular Medicine, University of Oslo, Oslo 0372, Norway.

Vestibulospinal neurons are organized into discrete groups projecting from brainstem to spinal cord, enabling vertebrates to maintain proper balance and posture. The two largest groups are the lateral vestibulospinal tract (LVST) group and the contralateral medial vestibulospinal tract (cMVST) group, with different projection lateralities and functional roles. In search of a molecular basis for these differences, we performed RNA sequencing on LVST and cMVST neurons from mouse and chicken embryos followed by immunohistofluorescence validation. Focusing on transcription factor (TF)-encoding genes, we identified TF signatures that uniquely distinguish the LVST from the cMVST group and further parse different rhombomere-derived portions comprising the cMVST group. Immunohistofluorescence assessment of the CNS from spinal cord to cortex demonstrated that these TF signatures are restricted to the respective vestibulospinal groups and some neurons in their immediate vicinity. Collectively, these results link the combinatorial expression of TFs to developmental and functional subdivisions within the vestibulospinal system.
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http://dx.doi.org/10.1523/ENEURO.0475-18.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6426439PMC
April 2019

Locomotor central pattern generator excitability states and serotonin sensitivity after spontaneous recovery from a neonatal lumbar spinal cord injury.

Brain Res 2019 04 4;1708:10-19. Epub 2018 Dec 4.

Norwegian Center for Stem Cell Research, Oslo University Hospital, Norway. Electronic address:

The spinal locomotor central pattern generator (CPG) in neonatal mice exhibits diverse output patterns, ranging from sub-rhythmic to multi-rhythmic to fictive locomotion, depending on its general level of excitation and neuromodulatory status. We have recently reported that the locomotor CPG in neonatal mice rapidly recovers the ability to produce neurochemically induced fictive locomotion following an upper lumbar spinal cord compression injury. Here we address the question of recovery of multi-rhythmic activity and the serotonin-sensitivity of the CPG. In isolated spinal cords from control and 3 days post-injury mice, application of dopamine and NMDA elicited multi-rhythmic activity with slow and fast components. The slow component comprised 10-20 s episodes of activity that were synchronous in ipsilateral or all lumbar ventral roots, and the fast components involved bursts within these episodes that displayed coordinated patterns of alternation between ipsilateral roots. Rhythm strength was the same in control and injured spinal cords. However, power spectral analysis of signal within episodes showed a reduced peak frequency after recovery. In control spinal cords, serotonin triggered fictive locomotion only when applied at high concentration (30 µM, constant NMDA). By contrast, in about 50% of injured preparations fictive locomotion was evoked by 2-3 times lower serotonin concentrations (10-15 µM). This increased serotonin sensitivity was correlated with post-injury changes in the expression of specific serotonin receptor transcripts, but not of dopamine receptor transcripts.
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http://dx.doi.org/10.1016/j.brainres.2018.12.001DOI Listing
April 2019

Acid-sensing ion channels emerged over 600 Mya and are conserved throughout the deuterostomes.

Proc Natl Acad Sci U S A 2018 08 30;115(33):8430-8435. Epub 2018 Jul 30.

Department of Drug Design and Pharmacology, Center for Biopharmaceuticals, University of Copenhagen, 2100 Copenhagen, Denmark.

Acid-sensing ion channels (ASICs) are proton-gated ion channels broadly expressed in the vertebrate nervous system, converting decreased extracellular pH into excitatory sodium current. ASICs were previously thought to be a vertebrate-specific branch of the DEG/ENaC family, a broadly conserved but functionally diverse family of channels. Here, we provide phylogenetic and experimental evidence that ASICs are conserved throughout deuterostome animals, showing that ASICs evolved over 600 million years ago. We also provide evidence of ASIC expression in the central nervous system of the tunicate, Furthermore, by comparing broadly related ASICs, we identify key molecular determinants of proton sensitivity and establish that proton sensitivity of the ASIC4 isoform was lost in the mammalian lineage. Taken together, these results suggest that contributions of ASICs to neuronal function may also be conserved broadly in numerous animal phyla.
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http://dx.doi.org/10.1073/pnas.1806614115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6099870PMC
August 2018

Advances in stem cell therapy for amyotrophic lateral sclerosis.

Expert Opin Biol Ther 2018 08;18(8):865-881

b Department of Biotechnology and Biosciences , University Milano Bicocca , Milano , Italy.

Introduction: Amyotrophic Lateral Sclerosis (ALS) is a progressive, incurable neurodegenerative disease that targets motoneurons. Cell-based therapies have generated widespread interest as a potential therapeutic approach but no conclusive results have yet been reported either from pre-clinical or clinical studies.

Areas Covered: This is an integrated review of pre-clinical and clinical studies focused on the development of cell-based therapies for ALS. We analyze the biology of stem cell treatments and results obtained from pre-clinical models of ALS and examine the methods and the results obtained to date from clinical trials. We discuss scientific, clinical, and ethical issues and propose some directions for future studies.

Expert Opinion: While data from individual studies are encouraging, stem-cell-based therapies do not yet represent a satisfactory, reliable clinical option. The field will critically benefit from the introduction of well-designed, randomized and reproducible, powered clinical trials. Comparative studies addressing key issues such as the nature, properties, and number of donor cells, the delivery mode and the selection of proper patient populations that may benefit the most from cell-based therapies are now of the essence. Multidisciplinary networks of experts should be established to empower effective translation of research into the clinic.
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http://dx.doi.org/10.1080/14712598.2018.1503248DOI Listing
August 2018

Dystonia-deafness syndrome caused by ACTB p.Arg183Trp heterozygosity shows striatal dopaminergic dysfunction and response to pallidal stimulation.

J Neurodev Disord 2018 05 22;10(1):17. Epub 2018 May 22.

Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

Background: Dystonia-deafness syndrome is a well-known clinical entity, with sensorineural deafness typically manifesting earlier than dystonia. ACTB p.Arg183Trp heterozygosity has been reported in six patients to cause combined infant-onset deafness and dystonia manifesting in adolescence or young adulthood. Three of these have received beneficial pallidal stimulation. Brain imaging to assess striatal function has not been reported previously, however. Nor has a comprehensive hypothesis been presented for how the pleiotropic manifestations of this specific beta-actin gene mutation originate developmentally.

Case Presentation: A 19-year-old girl with congenital mild dysmorphic facial features, cochlear implants for infant-onset deafness, and mild cognitive and emotional disability, presented with an adolescent-onset, severe generalized dystonia. Brain MRI and multiple single gene sequencing were inconclusive. Due to life-threatening dystonia, we implanted a neurostimulation device, targeting the postero-ventral internal pallidum bilaterally. The Burke-Fahn-Marsden Dystonia Rating Scale motor/disability scores improved from 87/25 to 21/13 at 2.5 months postoperatively, 26/14 at 3 years, and 30/14 at 4 years. Subsequent whole exome sequencing identified heterozygosity for the ACTB p.Arg183Trp variant. Brain imaging included I-ioflupane single photon emission computed tomography (Dopamine Transporter-SPECT), SPECT with I-epidepride (binds to dopamine type 2-receptors) and Fluoro-Deoxy-Glucose (FDG)-PET. Both Epidepride-SPECT and FDG-PET showed reduced tracer uptake in the striatum bilaterally, particularly in the putamen. DaT-SPECT was slightly abnormal.

Conclusions: In this patient with dystonia-deafness syndrome caused by ACTB p.Arg183Trp heterozygosity, unprecedented brain imaging findings strongly indicate striatal neuronal/dopaminergic dysfunction as the underlying cause of the dystonia. Pallidal stimulation provided a substantial improvement of the severe generalized dystonia, which is largely sustained at 4-year follow-up, and we advise this treatment to be considered in such patients. We hypothesize that the pleiotropic manifestations of the dystonia-deafness syndrome caused by this mutation derive from diverse developmental functions of beta-actin in neural crest migration and proliferation (facial dysmorphogenesis), hair cell stereocilia function (infant-onset deafness), and altered synaptic activity patterns associated with pubertal changes in striatal function (adolescent-onset dystonia). The temporal differences in developmental onset are likely due to varying degrees of susceptibility and of compensatory upregulation of other actin variants in the affected structures.
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http://dx.doi.org/10.1186/s11689-018-9235-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5964724PMC
May 2018

Wilhelm His' lasting insights into hindbrain and cranial ganglia development and evolution.

Dev Biol 2018 12 12;444 Suppl 1:S14-S24. Epub 2018 Feb 12.

Department of Biology, University of Iowa, Iowa, IA 52242, USA. Electronic address:

Wilhelm His (1831-1904) provided lasting insights into the development of the central and peripheral nervous system using innovative technologies such as the microtome, which he invented. 150 years after his resurrection of the classical germ layer theory of Wolff, von Baer and Remak, his description of the developmental origin of cranial and spinal ganglia from a distinct cell population, now known as the neural crest, has stood the test of time and more recently sparked tremendous advances regarding the molecular development of these important cells. In addition to his 1868 treatise on 'Zwischenstrang' (now neural crest), his work on the development of the human hindbrain published in 1890 provided novel ideas that more than 100 years later form the basis for penetrating molecular investigations of the regionalization of the hindbrain neural tube and of the migration and differentiation of its constituent neuron populations. In the first part of this review we briefly summarize the major discoveries of Wilhelm His and his impact on the field of embryology. In the second part we relate His' observations to current knowledge about the molecular underpinnings of hindbrain development and evolution. We conclude with the proposition, present already in rudimentary form in the writings of His, that a primordial spinal cord-like organization has been molecularly supplemented to generate hindbrain 'neomorphs' such as the cerebellum and the auditory and vestibular nuclei and their associated afferents and sensory organs.
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http://dx.doi.org/10.1016/j.ydbio.2018.02.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6087689PMC
December 2018

Rapid recovery and altered neurochemical dependence of locomotor central pattern generation following lumbar neonatal spinal cord injury.

J Physiol 2018 01 3;596(2):281-303. Epub 2017 Dec 3.

Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, University of Oslo, Oslo, Norway.

Key Points: Spinal compression injury targeted to the neonatal upper lumbar spinal cord, the region of highest hindlimb locomotor rhythmogenicity, leads to an initial paralysis of the hindlimbs. Behavioural recovery is evident within a few days and approaches normal function within about 3 weeks. Fictive locomotion in the isolated injured spinal cord cannot be elicited by a neurochemical cocktail containing NMDA, dopamine and serotonin 1 day post-injury, but can 3 days post-injury as readily as in the uninjured spinal cord. Low frequency coordinated rhythmic activity can be elicited in the isolated uninjured spinal cord by NMDA + dopamine (without serotonin), but not in the isolated injured spinal cord. In both the injured and uninjured spinal cord, eliciting bona fide fictive locomotion requires the additional presence of serotonin.

Abstract: Following incomplete compression injury in the thoracic spinal cord of neonatal mice 1 day after birth (P1), we previously reported that virtually normal hindlimb locomotor function is recovered within about 3 weeks despite substantial permanent thoracic tissue loss. Here, we asked whether similar recovery occurs following lumbar injury that impacts more directly on the locomotor central pattern generator (CPG). As in thoracic injuries, lumbar injuries caused about 90% neuronal loss at the injury site and increased serotonergic innervation below the injury. Motor recovery was slower after lumbar than thoracic injury, but virtually normal function was attained by P25 in both cases. Locomotor CPG status was tested by eliciting fictive locomotion in isolated spinal cords using a widely used neurochemical cocktail (NMDA, dopamine, serotonin). No fictive locomotion could be elicited 1 day post-injury, but could within 3 days post-injury as readily as in age-matched uninjured control spinal cords. Burst patterning and coordination were largely similar in injured and control spinal cords but there were differences. Notably, in both groups there were two main locomotor frequencies, but injured spinal cords exhibited a shift towards the higher frequency. Injury also altered the neurochemical dependence of locomotor CPG output, such that injured spinal cords, unlike control spinal cords, were incapable of generating low frequency rhythmic coordinated activity in the presence of NMDA and dopamine alone. Thus, the neonatal spinal cord also exhibits remarkable functional recovery after lumbar injuries, but the neurochemical sensitivity of locomotor circuitry is modified in the process.
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http://dx.doi.org/10.1113/JP274484DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5767688PMC
January 2018

Sensing External and Self-Motion with Hair Cells: A Comparison of the Lateral Line and Vestibular Systems from a Developmental and Evolutionary Perspective.

Brain Behav Evol 2017 9;90(2):98-116. Epub 2017 Oct 9.

Ludwig-Maximilians-Universität München, Department Biology II, Division of Neurobiology, Martinsried-Planegg, Germany.

Detection of motion is a feature essential to any living animal. In vertebrates, mechanosensory hair cells organized into the lateral line and vestibular systems are used to detect external water or head/body motion, respectively. While the neuronal components to detect these physical attributes are similar between the two sensory systems, the organizational pattern of the receptors in the periphery and the distribution of hindbrain afferent and efferent projections are adapted to the specific functions of the respective system. Here we provide a concise review comparing the functional organization of the vestibular and lateral line systems from the development of the organs to the wiring from the periphery and the first processing stages. The goal of this review is to highlight the similarities and differences to demonstrate how evolution caused a common neuronal substrate to adapt to different functions, one for the detection of external water stimuli and the generation of sensory maps and the other for the detection of self-motion and the generation of motor commands for immediate behavioral reactions.
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http://dx.doi.org/10.1159/000456646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5653922PMC
May 2018

Gaskell revisited: new insights into spinal autonomics necessitate a revised motor neuron nomenclature.

Cell Tissue Res 2017 11 31;370(2):195-209. Epub 2017 Aug 31.

Department of Molecular Medicine, University of Oslo, Oslo, Norway.

Several concepts developed in the nineteenth century have formed the basis of much of our neuroanatomical teaching today. Not all of these were based on solid evidence nor have withstood the test of time. Recent evidence on the evolution and development of the autonomic nervous system, combined with molecular insights into the development and diversification of motor neurons, challenges some of the ideas held for over 100 years about the organization of autonomic motor outflow. This review provides an overview of the original ideas and quality of supporting data and contrasts this with a more accurate and in depth insight provided by studies using modern techniques. Several lines of data demonstrate that branchial motor neurons are a distinct motor neuron population within the vertebrate brainstem, from which parasympathetic visceral motor neurons of the brainstem evolved. The lack of an autonomic nervous system in jawless vertebrates implies that spinal visceral motor neurons evolved out of spinal somatic motor neurons. Consistent with the evolutionary origin of brainstem parasympathetic motor neurons out of branchial motor neurons and spinal sympathetic motor neurons out of spinal motor neurons is the recent revision of the organization of the autonomic nervous system into a cranial parasympathetic and a spinal sympathetic division (e.g., there is no sacral parasympathetic division). We propose a new nomenclature that takes all of these new insights into account and avoids the conceptual misunderstandings and incorrect interpretation of limited and technically inferior data inherent in the old nomenclature.
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http://dx.doi.org/10.1007/s00441-017-2676-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5641259PMC
November 2017

Cellular reactions and compensatory tissue re-organization during spontaneous recovery after spinal cord injury in neonatal mice.

Dev Neurobiol 2017 09 17;77(8):928-946. Epub 2017 Feb 17.

Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, University of Oslo.

Following incomplete spinal cord injuries, neonatal mammals display a remarkable degree of behavioral recovery. Previously, we have demonstrated in neonatal mice a wholesale re-establishment and reorganization of synaptic connections from some descending axon tracts (Boulland et al.: PLoS One 8 (2013)). To assess the potential cellular mechanisms contributing to this recovery, we have here characterized a variety of cellular sequelae following thoracic compression injuries, focusing particularly on cell loss and proliferation, inflammation and reactive gliosis, and the dynamics of specific types of synaptic terminals. Early during the period of recovery, regressive events dominated. Tissue loss near the injury was severe, with about 80% loss of neurons and a similar loss of axons that later make up the white matter. There was no sign of neurogenesis, no substantial astroglial or microglial proliferation, no change in the ratio of M1 and M2 microglia and no appreciable generation of the terminal complement peptide C5a. One day after injury the number of synaptic terminals on lumbar motoneurons had dropped by a factor of 2, but normalized by 6 days. The ratio of VGLUT1/2+ to VGAT+ terminals remained similar in injured and uninjured spinal cords during this period. By 24 days after injury, when functional recovery is nearly complete, the density of 5-HT+ fibers below the injury site had increased by a factor of 2.5. Altogether this study shows that cellular reactions are diverse and dynamic. Pronounced recovery of both excitatory and inhibitory terminals and an increase in serotonergic innervation below the injury, coupled with a general lack of inflammation and reactive gliosis, are likely to contribute to the recovery. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 928-946, 2017.
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http://dx.doi.org/10.1002/dneu.22479DOI Listing
September 2017

A Neonatal Mouse Spinal Cord Compression Injury Model.

J Vis Exp 2016 Mar 27(109):e53498. Epub 2016 Mar 27.

Norwegian Center for Stem Cell Research, Oslo University Hospital; Laboratory of Neural Development and Optical Recording (NDEVOR), Department of Physiology, Institute of Basic Medical Sciences, University of Oslo;

Spinal cord injury (SCI) typically causes devastating neurological deficits, particularly through damage to fibers descending from the brain to the spinal cord. A major current area of research is focused on the mechanisms of adaptive plasticity that underlie spontaneous or induced functional recovery following SCI. Spontaneous functional recovery is reported to be greater early in life, raising interesting questions about how adaptive plasticity changes as the spinal cord develops. To facilitate investigation of this dynamic, we have developed a SCI model in the neonatal mouse. The model has relevance for pediatric SCI, which is too little studied. Because neural plasticity in the adult involves some of the same mechanisms as neural plasticity in early life(1), this model may potentially have some relevance also for adult SCI. Here we describe the entire procedure for generating a reproducible spinal cord compression (SCC) injury in the neonatal mouse as early as postnatal (P) day 1. SCC is achieved by performing a laminectomy at a given spinal level (here described at thoracic levels 9-11) and then using a modified Yasargil aneurysm mini-clip to rapidly compress and decompress the spinal cord. As previously described, the injured neonatal mice can be tested for behavioral deficits or sacrificed for ex vivo physiological analysis of synaptic connectivity using electrophysiological and high-throughput optical recording techniques(1). Earlier and ongoing studies using behavioral and physiological assessment have demonstrated a dramatic, acute impairment of hindlimb motility followed by a complete functional recovery within 2 weeks, and the first evidence of changes in functional circuitry at the level of identified descending synaptic connections(1).
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http://dx.doi.org/10.3791/53498DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4841318PMC
March 2016

Hampered Lung Maturation in Methimazole-Induced Hypothyroidism in Fetal Chicken: Morphological and Molecular Correlates to Human Fetal Development.

Neonatology 2016 13;110(2):83-92. Epub 2016 Apr 13.

Department of Pathology, Oslo University Hospital HF, Ullevx00E5;l, Oslo, Norway.

Background: Molecular understanding of lung development is crucial for developing therapies and diagnostic tools. Animal models with altered thyroid hormone signaling provide mechanistic insight into thyroid-dependent neonatal lung disease. Repression of Klf2 (Krüppel-like factor 2), a suggested T3 target gene, is associated with disrupted lung development in mice. Klf2 is proposed to be specifically involved in type I pneumocyte differentiation.

Objectives: To explore mechanisms of thyroid-dependent lung disease, we studied developing chicken fetuses with experimentally induced hypothyroidism.

Methods: Morphology and the expression of a panel of molecules linked to Klf2 were assessed using histology, immunohistochemistry, Western blot and qPCR.

Results: Methimazole injections at E14 hampered lung maturation. The effects of methimazole were evident in several tissue compartments, and impacted on both pneumocyte and vascular differentiation, suggesting cellular and molecular pleiotropy.

Conclusions: Concomitant expression changes in a panel of selected microRNAs regulated by Klf2 suggest importance in lung development. These microRNAs may thus represent potential clinical targets and diagnostic and prognostic tools in thyroid-dependent lung disease.
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http://dx.doi.org/10.1159/000444656DOI Listing
November 2017

Loss of Projections, Functional Compensation, and Residual Deficits in the Mammalian Vestibulospinal System of Hoxb1-Deficient Mice.

eNeuro 2015 Nov-Dec;2(6). Epub 2015 Dec 26.

Division of Physiology, Department of Molecular Medicine, University of Oslo, 0317 Oslo, Norway; Norwegian Center for Stem Cell Research, Oslo University Hospital, 0317 Oslo, Norway.

The genetic mechanisms underlying the developmental and functional specification of brainstem projection neurons are poorly understood. Here, we use transgenic mouse tools to investigate the role of the gene Hoxb1 in the developmental patterning of vestibular projection neurons, with particular focus on the lateral vestibulospinal tract (LVST). The LVST is the principal pathway that conveys vestibular information to limb-related spinal motor circuits and arose early during vertebrate evolution. We show that the segmental hindbrain expression domain uniquely defined by the rhombomere 4 (r4) Hoxb1 enhancer is the origin of essentially all LVST neurons, but also gives rise to subpopulations of contralateral medial vestibulospinal tract (cMVST) neurons, vestibulo-ocular neurons, and reticulospinal (RS) neurons. In newborn mice homozygous for a Hoxb1-null mutation, the r4-derived LVST and cMVST subpopulations fail to form and the r4-derived RS neurons are depleted. Several general motor skills appear unimpaired, but hindlimb vestibulospinal reflexes, which are mediated by the LVST, are greatly reduced. This functional deficit recovers, however, during the second postnatal week, indicating a substantial compensation for the missing LVST. Despite the compensatory plasticity in balance, adult Hoxb1-null mice exhibit other behavioral deficits that manifest particularly in proprioception and interlimb coordination during locomotor tasks. Our results provide a comprehensive account of the developmental role of Hoxb1 in patterning the vestibular system and evidence for a remarkable developmental plasticity in the descending control of reflex limb movements. They also suggest an involvement of the lateral vestibulospinal tract in proprioception and in ensuring limb alternation generated by locomotor circuitry.
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http://dx.doi.org/10.1523/ENEURO.0096-15.2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4697082PMC
September 2016

Early postnatal maturation in vestibulospinal pathways involved in neck and forelimb motor control.

Dev Neurobiol 2016 10 22;76(10):1061-77. Epub 2016 Jan 22.

Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

To assess the organization and functional development of vestibulospinal inputs to cervical motoneurons (MNs), we have used electrophysiology (ventral root and electromyographic [EMG] recording), calcium imaging, trans-synaptic rabies virus (RV) and conventional retrograde tracing and immunohistochemistry in the neonatal mouse. By stimulating the VIIIth nerve electrically while recording synaptically mediated calcium responses in MNs, we characterized the inputs from the three vestibulospinal tracts, the separate ipsilateral and contralateral medial vestibulospinal tracts (iMVST/cMVST) and the lateral vestibulospinal tract (LVST), to MNs in the medial and lateral motor columns (MMC and LMC) of cervical segments. We found that ipsilateral inputs from the iMVST and LVST were differentially distributed to the MMC and LMC in the different segments, and that all contralateral inputs to MMC and LMC MNs in each segment derive from the cMVST. Using trans-synaptic RV retrograde tracing as well as pharmacological manipulation of VIIIth nerve-elicited synaptic responses, we found that a substantial proportion of inputs to both neck and forelimb extensor MNs was mediated monosynaptically, but that polysynaptic inputs were also significant. By recording EMG responses evoked by natural stimulation of the vestibular apparatus, we found that vestibular-mediated motor output to the neck and forelimb musculature became more robust during the first 10 postnatal days, concurrently with a decrease in the latency of MN discharge evoked by VIIIth nerve electrical stimulation. Together, these results provide insight into the complexity of vestibulospinal connectivity in the cervical spinal cord and a cogent demonstration of the functional maturation that vestibulospinal connections undergo postnatally. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1061-1077, 2016.
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http://dx.doi.org/10.1002/dneu.22375DOI Listing
October 2016

Developmental Characterization of Tail Movements in the Appendicularian Urochordate Oikopleura dioica.

Brain Behav Evol 2015 2;86(3-4):191-209. Epub 2015 Nov 2.

Sars International Centre for Marine Molecular Biology, University of Oslo, Oslo, Norway.

Using high-speed video cinematography, we characterized kinematically the spontaneous tail movements made by the appendicularian urochordate Oikopleura dioica. Videos of young adult (1-day-old) animals discriminated 4 cardinal movement types: bending, nodding, swimming and filtering, each of which had a characteristic signature including cyclicity, event or cycle duration, cycle frequency, cycle frequency variation, laterality, tail muscle segment coordination and episode duration. Bending exhibited a more common, unilateral form (single bending) and a rarer, bilateral form (alternating bending). Videos of developing animals showed that bending and swimming appeared in rudimentary form starting just after hatching and exhibited developmental changes in movement excursion, duration and frequency, whereas nodding and filtering appeared in the fully mature form in young adults at the time of first house production. More complex behaviors were associated with inflating, entering and exiting the house. We also assessed the influence of descending inputs by separating the tail (which contains all muscles and most likely the neural circuits that generate most motor outputs) from the head. Isolated tails spontaneously generated either bending or swimming movements in abnormally protracted episodes. This together with other observations of interactions between bending and swimming behaviors indicates the presence of several types of descending inputs that regulate the activity of the pattern generating circuitry in the tail nervous system.
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http://dx.doi.org/10.1159/000439517DOI Listing
September 2016

Pontine reticulospinal projections in the neonatal mouse: Internal organization and axon trajectories.

J Comp Neurol 2016 Apr 10;524(6):1270-91. Epub 2015 Oct 10.

Laboratory of Neural Development and Optical Recording (NDEVOR), Department of Physiology, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, 0316, Oslo, Norway.

We recently characterized physiologically a pontine reticulospinal (pRS) projection in the neonatal mouse that mediates synaptic effects on spinal motoneurons via parallel uncrossed and crossed pathways (Sivertsen et al. [2014] J Neurophysiol 112:1628-1643). Here we characterize the origins, anatomical organization, and supraspinal axon trajectories of these pathways via retrograde tracing from the high cervical spinal cord. The two pathways derive from segregated populations of ipsilaterally and contralaterally projecting pRS neurons with characteristic locations within the pontine reticular formation (PRF). We obtained estimates of relative neuron numbers by counting from sections, digitally generated neuron position maps, and 3D reconstructions. Ipsilateral pRS neurons outnumber contralateral pRS neurons by threefold and are distributed about equally in rostral and caudal regions of the PRF, whereas contralateral pRS neurons are concentrated in the rostral PRF. Ipsilateral pRS neuron somata are on average larger than contralateral. No pRS neurons are positive in transgenic mice that report the expression of GAD, suggesting that they are predominantly excitatory. Putative GABAergic interneurons are interspersed among the pRS neurons, however. Ipsilateral and contralateral pRS axons have distinctly different trajectories within the brainstem. Their initial spinal funicular trajectories also differ, with ipsilateral and contralateral pRS axons more highly concentrated medially and laterally, respectively. The larger size and greater number of ipsilateral vs. contralateral pRS neurons is compatible with our previous finding that the uncrossed projection transmits more reliably to spinal motoneurons. The information about supraspinal and initial spinal pRS axon trajectories should facilitate future physiological assessment of synaptic connections between pRS neurons and spinal neurons.
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http://dx.doi.org/10.1002/cne.23904DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4851107PMC
April 2016

Targeting PBK/TOPK decreases growth and survival of glioma initiating cells in vitro and attenuates tumor growth in vivo.

Mol Cancer 2015 Jun 17;14:121. Epub 2015 Jun 17.

Vilhelm Magnus Laboratory for Neurosurgical Research, Department of Neurosurgery and Institute of Surgical Research, Oslo University Hospital, Oslo, Norway.

Background: Glioblastomas are invasive therapy resistant brain tumors with extremely poor prognosis. The Glioma initiating cell (GIC) population contributes to therapeutic resistance and tumor recurrence. Targeting GIC-associated gene candidates could significantly impact GBM tumorigenicity. Here, we investigate a protein kinase, PBK/TOPK as a candidate for regulating growth, survival and in vivo tumorigenicity of GICs.

Methods: PBK is highly upregulated in GICs and GBM tissues as shown by RNA and protein analyses. We knocked down PBK using shRNA vectors and inhibited the function of PBK protein with a pharmacological PBK inhibitor, HITOPK-032. We assessed viability, tumorsphere formation and apoptosis in three patient derived GIC cultures.

Results: Gene knockdown of PBK led to decreased viability and sphere formation and in one culture an increase in apoptosis. Treatment of cells with inhibitor HITOPK-032 (5 μM and 10 μM) almost completely abolished growth and elicited a large increase in apoptosis in all three cultures. HI-TOPK-032 treatment (5 mg/kg and 10 mg/kg bodyweight) in vivo resulted in diminished growth of experimentally induced subcutaneous GBM tumors in mice. We also carried out multi-culture assays of cell survival to investigate the relative effects on GICs compared with the normal neural stem cells (NSCs) and their differentiated counterparts. Normal NSCs seemed to withstand treatment slightly better than the GICs.

Conclusion: Our study of identification and functional validation of PBK suggests that this candidate can be a promising molecular target for GBM treatment.
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http://dx.doi.org/10.1186/s12943-015-0398-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470057PMC
June 2015

Segmental organization of vestibulospinal inputs to spinal interneurons mediating crossed activation of thoracolumbar motoneurons in the neonatal mouse.

J Neurosci 2015 May;35(21):8158-69

Laboratory of Neural Development and Optical Recording, Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway, Norwegian Center for Stem Cell Research, Oslo University Hospital, N-0372 Oslo, Norway,

Vestibulospinal pathways activate contralateral motoneurons (MNs) in the thoracolumbar spinal cord of the neonatal mouse exclusively via axons descending ipsilaterally from the vestibular nuclei via the lateral vestibulospinal tract (LVST; Kasumacic et al., 2010). Here we investigate how transmission from the LVST to contralateral MNs is mediated by descending commissural interneurons (dCINs) in different spinal segments. We test the polysynaptic nature of this crossed projection by assessing LVST-mediated ventral root (VR) response latencies, manipulating synaptic responses pharmacologically, and tracing the pathway transynaptically from hindlimb extensor muscles using rabies virus (RV). Longer response latencies in contralateral than ipsilateral VRs, near-complete abolition of LVST-mediated calcium responses in contralateral MNs by mephenesin, and the absence of transsynaptic RV labeling of contralateral LVST neurons within a monosynaptic time window all indicate an overwhelmingly polysynaptic pathway from the LVST to contralateral MNs. Optical recording of synaptically mediated calcium responses identifies LVST-responsive ipsilateral dCINs that exhibit segmental differences in proportion and dorsoventral distribution. In contrast to thoracic and lower lumbar segments, in which most dCINs are LVST responsive, upper lumbar segments stand out because they contain a much smaller and more ventrally restricted subpopulation of LVST-responsive dCINs. A large proportion of these upper lumbar LVST-responsive dCINs project to contralateral L5, which contains many of the hindlimb extensor MNs activated by the LVST. A selective channeling of LVST inputs through segmentally and dorsoventrally restricted subsets of dCINs provides a mechanism for targeting vestibulospinal signals differentially to contralateral trunk and hindlimb MNs in the mammalian spinal cord.
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http://dx.doi.org/10.1523/JNEUROSCI.5188-14.2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4444539PMC
May 2015

Modification of the larval swimming behavior in Oikopleura dioica, a chordate with a miniaturized central nervous system by dsRNA injection into fertilized eggs.

J Exp Zool B Mol Dev Evol 2015 Mar 11;324(2):114-27. Epub 2015 Feb 11.

Sars International Centre for Marine Molecular Biology, University of Bergen, Norway.

Using RNA interference, we have selectively perturbed neurotransmitter-related features of the larval swimming behavior of Oikopleura dioica, a tunicate with a central nervous system comprising about 130 neurons. We injected dsRNA into fertilized eggs to knockdown the expression of the genes, respectively, encoding ChAT (choline acetyltransferase) and GAD (glutamic acid decarboxylase), enzymes critical for the biosynthesis of acetylcholine and GABA. These two neurotransmitters have conserved roles during evolution, particularly within chordate motor systems, where they mediate respectively neuromuscular and central inhibitory signals. In Oikopleura, interference with ChAT expression prevented the normal bidirectional, propagating tail movement characteristic of swimming, permitting only repeated unilateral tail bends. Proper swimming was never observed, and the resting period between episodes of activity was lengthened. This phenotype is most likely caused by the reduction of transcription observed for both the targeted ChAT gene and the VAChT gene (Vesicular Acetylcholine Transporter), both genes being transcribed from the same operon. Interference with GAD expression led to an uncoordinated version of swimming with a spiral movement trajectory, but with episodes similar in duration and cycle frequency to those of normal swimming. Our results suggest locomotor functions for ChAT and GABA that are more subtle than previously proposed for tunicates and opens the way for a genetic dissection of Oikopleura neuronal circuits, which are likely to be among the most simplified in the chordate phylum.
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http://dx.doi.org/10.1002/jez.b.22607DOI Listing
March 2015

Sim1 is required for the migration and axonal projections of V3 interneurons in the developing mouse spinal cord.

Dev Neurobiol 2015 Sep 18;75(9):1003-17. Epub 2015 Feb 18.

Department of Medical Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2.

V3 spinal interneurons (INs) are a group of excitatory INs that play a crucial role in producing balanced and stable gaits in vertebrate animals. In the developing mouse spinal cord, V3 INs arise from the most ventral progenitor domain and form anatomically distinctive subpopulations in adult spinal cords. They are marked by the expression of transcription factor Sim1 postmitotically, but the function of Sim1 in V3 development remains unknown. Here, we used Sim1(Cre) ;tdTomato mice to trace the fate of V3 INs in a Sim1 mutant versus control genetic background during development. In Sim1 mutants, V3 INs are produced normally and maintain a similar position and organization as in wild types before E12.5. Further temporal analysis revealed that the V3 INs in the mutants failed to migrate properly to form V3 subgroups along the dorsoventral axis of the spinal cord. At birth, in the Sim1 mutant the number of V3 INs in the ventral subgroup was normal, but they were significantly reduced in the dorsal subgroup with a concomitant increase in the intermediate subgroup. Retrograde labeling at lumbar level revealed that loss of Sim1 led to a reduction in extension of contralateral axon projections both at E14.5 and P0 without affecting ipsilateral axon projections. These results demonstrate that Sim1 is essential for proper migration and the guidance of commissural axons of the spinal V3 INs.
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http://dx.doi.org/10.1002/dneu.22266DOI Listing
September 2015

Organization of pontine reticulospinal inputs to motoneurons controlling axial and limb muscles in the neonatal mouse.

J Neurophysiol 2014 Oct 18;112(7):1628-43. Epub 2014 Jun 18.

Department of Physiology, Emory University School of Medicine, Atlanta, Georgia

Using optical recording of synaptically mediated calcium transients and selective spinal lesions, we investigated the pattern of activation of spinal motoneurons (MNs) by the pontine reticulospinal projection in isolated brain stem-spinal cord preparations from the neonatal mouse. Stimulation sites throughout the region where the pontine reticulospinal neurons reside reliably activated MNs at cervical, thoracic, and lumbar levels. Activation was similar in MNs ipsi- and contralateral to the stimulation site, similar in medial and lateral motor columns that contain trunk and limb MNs, respectively, and similar in the L2 and L5 segments that predominantly contain flexor and extensor MNs, respectively. In nonlesioned preparations, responses in both ipsi- and contralateral MNs followed individual stimuli in stimulus trains nearly one-to-one (with few failures). After unilateral hemisection at C1 on the same side as the stimulation, responses had substantially smaller magnitudes and longer latencies and no longer followed individual stimuli. After unilateral hemisection at C1 on the side opposite to the stimulation, the responses were also smaller, but their latencies were not affected. Thus we distinguish two pontine reticulospinal pathways to spinal MNs, one uncrossed and the other crossed, of which the uncrossed pathway transmits more faithfully and appears to be more direct.
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http://dx.doi.org/10.1152/jn.00820.2013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4631545PMC
October 2014