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Kröger S, Watkins B. Muscle spindle function in healthy and diseased muscle. Skelet Muscle 2021; 11:3. [PMID: 33407830 PMCID: PMC7788844 DOI: 10.1186/s13395-020-00258-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 12/20/2020] [Indexed: 12/16/2022] Open
Abstract
Almost every muscle contains muscle spindles. These delicate sensory receptors inform the central nervous system (CNS) about changes in the length of individual muscles and the speed of stretching. With this information, the CNS computes the position and movement of our extremities in space, which is a requirement for motor control, for maintaining posture and for a stable gait. Many neuromuscular diseases affect muscle spindle function contributing, among others, to an unstable gait, frequent falls and ataxic behavior in the affected patients. Nevertheless, muscle spindles are usually ignored during examination and analysis of muscle function and when designing therapeutic strategies for neuromuscular diseases. This review summarizes the development and function of muscle spindles and the changes observed under pathological conditions, in particular in the various forms of muscular dystrophies.
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Affiliation(s)
- Stephan Kröger
- Department of Physiological Genomics, Biomedical Center, Ludwig-Maximilians-University Munich, Großhaderner Str. 9, 82152, Planegg-Martinsried, Germany.
| | - Bridgette Watkins
- Department of Physiological Genomics, Biomedical Center, Ludwig-Maximilians-University Munich, Großhaderner Str. 9, 82152, Planegg-Martinsried, Germany
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2
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A Role for Sensory end Organ-Derived Signals in Regulating Muscle Spindle Proprioceptor Phenotype. J Neurosci 2019; 39:4252-4267. [PMID: 30926747 DOI: 10.1523/jneurosci.2671-18.2019] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 02/21/2019] [Accepted: 03/21/2019] [Indexed: 01/09/2023] Open
Abstract
Proprioceptive feedback from Group Ia/II muscle spindle afferents and Group Ib Golgi tendon afferents is critical for the normal execution of most motor tasks, yet how these distinct proprioceptor subtypes emerge during development remains poorly understood. Using molecular genetic approaches in mice of either sex, we identified 24 transcripts that have not previously been associated with a proprioceptor identity. Combinatorial expression analyses of these markers reveal at least three molecularly distinct proprioceptor subtypes. In addition, we find that 12 of these transcripts are expressed well after proprioceptors innervate their respective sensory receptors, and expression of three of these markers, including the heart development molecule Heg1, is significantly reduced in mice that lack muscle spindles. These data reveal Heg1 as a putative marker for proprioceptive muscle spindle afferents. Moreover, they suggest that the phenotypic specialization of functionally distinct proprioceptor subtypes depends, in part, on extrinsic sensory receptor organ-derived signals.SIGNIFICANCE STATEMENT Sensory feedback from muscle spindle (MS) and Golgi tendon organ (GTO) sensory end organs is critical for normal motor control, but how distinct MS and GTO afferent sensory neurons emerge during development remains poorly understood. Using (bulk) transcriptome analysis of genetically identified proprioceptors, this work reveals molecular markers for distinct proprioceptor subsets, including some that appear selectively expressed in MS afferents. Detailed analysis of the expression of these transcripts provides evidence that MS/GTO afferent subtype phenotypes may, at least in part, emerge through extrinsic, sensory end organ-derived signals.
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Kathe C, Moon LDF. RNA sequencing dataset describing transcriptional changes in cervical dorsal root ganglia after bilateral pyramidotomy and forelimb intramuscular gene therapy with an adeno-associated viral vector encoding human neurotrophin-3. Data Brief 2018; 21:377-385. [PMID: 30364576 PMCID: PMC6197729 DOI: 10.1016/j.dib.2018.09.099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 09/26/2018] [Accepted: 09/29/2018] [Indexed: 10/31/2022] Open
Abstract
Unilateral or bilateral corticospinal tract injury in the medullary pyramids in adult rats causes anatomical and physiological changes in proprioceptive neurons projecting to the cervical spinal cord accompanied by hyperreflexia and abnormal behavioural movements including spasms. In a previous publication, we showed that "Intramuscular Neurotrophin-3 normalizes low threshold spinal reflexes, reduces spasms and improves mobility after bilateral corticospinal tract injury in rats" (Kathe et al., 2016) [1]. We hypothesize that neurotrophin-3 induces these changes by modifying gene expression in affected cervical dorsal root ganglia (DRG). Therefore in this data article, we analyzed the transcriptomes of cervical DRGs obtained during that previous study from naïve rats and from rats after bilateral pyramidotomy (bPYX) with unilateral intramuscular injections of either AAV1-CMV-NT3 or AAV1-CMV-EGFP applied 24 h after injury (Kathe et al., 2016) [1]. A bioinformatic analysis enabled us to identify genes that are likely to be expressed in TrkC+ neurons after injury and which were regulated by neurotrophin-3 in the direction expected from other datasets involving knockout or overexpression of neurotrophin-3. This dataset will help us and others identify genes in sensory neurons whose expression levels are regulated by neurotrophin-3 treatment. This may help identify novel therapeutic targets to improve sensation and movement after neurological injury. Data has been deposited in the Gene Expression Omnibus (GSE82197), http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?token=avgpicgcjhknzyv&acc=GSE82197.
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Affiliation(s)
- Claudia Kathe
- Neurorestoration Group, Wolfson Centre for Age Related Diseases, King׳s College, London, UK.,Center for Neuroprosthetics, Brain Mind Institute, Campus Biotech, École Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Lawrence D F Moon
- Neurorestoration Group, Wolfson Centre for Age Related Diseases, King׳s College, London, UK
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4
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5
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Li C, Wang S, Chen Y, Zhang X. Somatosensory Neuron Typing with High-Coverage Single-Cell RNA Sequencing and Functional Analysis. Neurosci Bull 2017; 34:200-207. [PMID: 28612318 PMCID: PMC5799126 DOI: 10.1007/s12264-017-0147-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 05/04/2017] [Indexed: 12/27/2022] Open
Abstract
Different physical and chemical stimuli are detected by the peripheral sensory receptors of dorsal root ganglion (DRG) neurons, and the generated inputs are transmitted via afferent fibers into the central nervous system. The gene expression profiles of DRG neurons contribute to the generation, transmission, and regulation of various somatosensory signals. Recently, the single-cell transcriptomes, cell types, and functional annotations of somatosensory neurons have been studied. In this review, we introduce our classification of DRG neurons based on single-cell RNA-sequencing and functional analyses, and discuss the technical approaches. Moreover, studies on the molecular and cellular mechanisms underlying somatic sensations are discussed.
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Affiliation(s)
- Changlin Li
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Center for Excellence in Brain Science, Chinese Academy of Sciences, Shanghai, 200031, China
| | - Sashuang Wang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Center for Excellence in Brain Science, Chinese Academy of Sciences, Shanghai, 200031, China.,School of Life Science and Technology, ShanghaiTec University, Shanghai, 200031, China
| | - Yan Chen
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Center for Excellence in Brain Science, Chinese Academy of Sciences, Shanghai, 200031, China
| | - Xu Zhang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Center for Excellence in Brain Science, Chinese Academy of Sciences, Shanghai, 200031, China. .,School of Life Science and Technology, ShanghaiTec University, Shanghai, 200031, China.
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6
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Kathe C, Hutson TH, McMahon SB, Moon LDF. Intramuscular Neurotrophin-3 normalizes low threshold spinal reflexes, reduces spasms and improves mobility after bilateral corticospinal tract injury in rats. eLife 2016; 5. [PMID: 27759565 PMCID: PMC5070949 DOI: 10.7554/elife.18146] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 09/22/2016] [Indexed: 12/12/2022] Open
Abstract
Brain and spinal injury reduce mobility and often impair sensorimotor processing in the spinal cord leading to spasticity. Here, we establish that complete transection of corticospinal pathways in the pyramids impairs locomotion and leads to increased spasms and excessive mono- and polysynaptic low threshold spinal reflexes in rats. Treatment of affected forelimb muscles with an adeno-associated viral vector (AAV) encoding human Neurotrophin-3 at a clinically-feasible time-point after injury reduced spasticity. Neurotrophin-3 normalized the short latency Hoffmann reflex to a treated hand muscle as well as low threshold polysynaptic spinal reflexes involving afferents from other treated muscles. Neurotrophin-3 also enhanced locomotor recovery. Furthermore, the balance of inhibitory and excitatory boutons in the spinal cord and the level of an ion co-transporter in motor neuron membranes required for normal reflexes were normalized. Our findings pave the way for Neurotrophin-3 as a therapy that treats the underlying causes of spasticity and not only its symptoms. DOI:http://dx.doi.org/10.7554/eLife.18146.001 Injuries to the brain and spinal cord cause disability in millions of people worldwide. Physical rehabilitation can restore some muscle control and improve mobility in affected individuals. However, no current treatments provide long-term relief from the unwanted muscle contractions and spasms that affect as many as 78% of people with a spinal cord injury. These spasms can seriously hamper a person’s ability to carry out day-to-day tasks and get around independently. A few treatments can help in the short term but have side effects; indeed while Botox injections are used to paralyse the muscle, these also reduce the chances of useful improvements. As such, better therapies for muscle spasms are needed; especially ones that reduce spasms in the arms. Rats with injuries to the spinal cord between their middle to lower back typically develop spasms in their legs or tail, and rat models have helped scientists begin to understand why these involuntary movements occur. Now, Kathe et al. report that cutting one specific pathway that connects the brain to the spinal cord in anesthetised rats leads to the development of spasms in the forelimbs as well. Several months after the surgery, the rats had spontaneous muscle contractions in their forelimbs and walked abnormally. Further experiments showed that some other neural pathways in the rats became incorrectly wired and hyperactive and that this resulted in the abnormal movements. Next, Kathe et al. asked whether using gene therapy to deliver a protein that is required for neural circuits to form between muscles and the spinal cord (called neurotrophin-3) would stop the involuntary movements in the forelimbs. Delivering the gene therapy directly into the forelimb muscles of the disabled rats a day after their injury increased the levels of neurotrophin-3 in these muscles. Rats that received this treatment had fewer spasms and walked better than those that did not. Further experiments confirmed that this was because the rats’ previously hyperactive and abnormally wired neural circuits became more normal after the treatment. Together these results suggest that neurotrophin-3 might be a useful treatment for muscle spasms in people with spinal injury. There have already been preliminary studies in people showing that treatment with neurotrophin-3 is safe and well tolerated. Future studies are needed to confirm that it could be useful in humans. DOI:http://dx.doi.org/10.7554/eLife.18146.002
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Affiliation(s)
- Claudia Kathe
- Neurorestoration Department, Wolfson Centre for Age-Related Diseases, King's College London, University of London, London, United Kingdom
| | - Thomas Haynes Hutson
- Division of Brain Sciences, Department of Medicine, Imperial College London, London, United Kingdom
| | - Stephen Brendan McMahon
- Neurorestoration Department, Wolfson Centre for Age-Related Diseases, King's College London, University of London, London, United Kingdom
| | - Lawrence David Falcon Moon
- Neurorestoration Department, Wolfson Centre for Age-Related Diseases, King's College London, University of London, London, United Kingdom
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7
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Duricki DA, Hutson TH, Kathe C, Soleman S, Gonzalez-Carter D, Petruska JC, Shine HD, Chen Q, Wood TC, Bernanos M, Cash D, Williams SCR, Gage FH, Moon LDF. Delayed intramuscular human neurotrophin-3 improves recovery in adult and elderly rats after stroke. Brain 2015; 139:259-75. [PMID: 26614754 PMCID: PMC4785394 DOI: 10.1093/brain/awv341] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 09/29/2015] [Indexed: 12/11/2022] Open
Abstract
There is an urgent need for a therapy that reverses disability after stroke when initiated in a time frame suitable for the majority of new victims. We show here that intramuscular delivery of neurotrophin-3 (NT3, encoded by NTF3) can induce sensorimotor recovery when treatment is initiated 24 h after stroke. Specifically, in two randomized, blinded preclinical trials, we show improved sensory and locomotor function in adult (6 months) and elderly (18 months) rats treated 24 h following cortical ischaemic stroke with human NT3 delivered using a clinically approved serotype of adeno-associated viral vector (AAV1). Importantly, AAV1-hNT3 was given in a clinically-feasible timeframe using a straightforward, targeted route (injections into disabled forelimb muscles). Magnetic resonance imaging and histology showed that recovery was not due to neuroprotection, as expected given the delayed treatment. Rather, treatment caused corticospinal axons from the less affected hemisphere to sprout in the spinal cord. This treatment is the first gene therapy that reverses disability after stroke when administered intramuscularly in an elderly body. Importantly, phase I and II clinical trials by others show that repeated, peripherally administered high doses of recombinant NT3 are safe and well tolerated in humans with other conditions. This paves the way for NT3 as a therapy for stroke.
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Affiliation(s)
- Denise A Duricki
- 1 Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, 16-18 Newcomen Street, London SE1 1UL, UK 2 Centre for Integrative Biology, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
| | - Thomas H Hutson
- 1 Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, 16-18 Newcomen Street, London SE1 1UL, UK 3 Division of Brain Sciences, Department of Medicine, Hammersmith Campus, Imperial College London, London, UK
| | - Claudia Kathe
- 1 Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, 16-18 Newcomen Street, London SE1 1UL, UK
| | - Sara Soleman
- 1 Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, 16-18 Newcomen Street, London SE1 1UL, UK 4 John Van Geest Centre for Brain Repair University of Cambridge, The E.D. Adrian Building, Forvie Site, Robinson Way Cambridge, CB2 0PY, UK
| | - Daniel Gonzalez-Carter
- 1 Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, 16-18 Newcomen Street, London SE1 1UL, UK 3 Division of Brain Sciences, Department of Medicine, Hammersmith Campus, Imperial College London, London, UK
| | - Jeffrey C Petruska
- 5 Department of Anatomical Sciences and Neurobiology, University of Louisville; Kentucky Spinal Cord Injury Research Center, Department of Neurological Surgery, Louisville, Kentucky, USA
| | - H David Shine
- 6 Center for Cell and Gene Therapy, Department of Neuroscience, Alkek Bldg N1130.01, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - Qin Chen
- 6 Center for Cell and Gene Therapy, Department of Neuroscience, Alkek Bldg N1130.01, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - Tobias C Wood
- 7 Neuroimaging Research Group, King's College London, PO42 De Crespigny Park, London, SE5 8AF, UK
| | - Michel Bernanos
- 7 Neuroimaging Research Group, King's College London, PO42 De Crespigny Park, London, SE5 8AF, UK
| | - Diana Cash
- 7 Neuroimaging Research Group, King's College London, PO42 De Crespigny Park, London, SE5 8AF, UK
| | - Steven C R Williams
- 7 Neuroimaging Research Group, King's College London, PO42 De Crespigny Park, London, SE5 8AF, UK
| | - Fred H Gage
- 8 The Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, La Jolla, CA 92037, USA
| | - Lawrence D F Moon
- 1 Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, 16-18 Newcomen Street, London SE1 1UL, UK 2 Centre for Integrative Biology, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
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8
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Chiu IM, Barrett LB, Williams EK, Strochlic DE, Lee S, Weyer AD, Lou S, Bryman GS, Roberson DP, Ghasemlou N, Piccoli C, Ahat E, Wang V, Cobos EJ, Stucky CL, Ma Q, Liberles SD, Woolf CJ. Transcriptional profiling at whole population and single cell levels reveals somatosensory neuron molecular diversity. eLife 2014; 3. [PMID: 25525749 PMCID: PMC4383053 DOI: 10.7554/elife.04660] [Citation(s) in RCA: 165] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 12/18/2014] [Indexed: 12/17/2022] Open
Abstract
The somatosensory nervous system is critical for the organism's ability to respond to
mechanical, thermal, and nociceptive stimuli. Somatosensory neurons are functionally
and anatomically diverse but their molecular profiles are not well-defined. Here, we
used transcriptional profiling to analyze the detailed molecular signatures of dorsal
root ganglion (DRG) sensory neurons. We used two mouse reporter lines and surface IB4
labeling to purify three major non-overlapping classes of neurons: 1)
IB4+SNS-Cre/TdTomato+, 2)
IB4−SNS-Cre/TdTomato+, and 3)
Parv-Cre/TdTomato+ cells, encompassing the majority of
nociceptive, pruriceptive, and proprioceptive neurons. These neurons displayed
distinct expression patterns of ion channels, transcription factors, and GPCRs.
Highly parallel qRT-PCR analysis of 334 single neurons selected by membership of the
three populations demonstrated further diversity, with unbiased clustering analysis
identifying six distinct subgroups. These data significantly increase our knowledge
of the molecular identities of known DRG populations and uncover potentially novel
subsets, revealing the complexity and diversity of those neurons underlying
somatosensation. DOI:http://dx.doi.org/10.7554/eLife.04660.001 In the nervous system, a network of specialized neurons—known as the
somatosensory system—carries information about sensations including touch,
muscle position, temperature and pain. Distinct sets of somatosensory neurons are
thought to carry information about the different types of sensations. In young
animals, the precise switching on, or ‘expression’, of genes controls
the formation of the network of neurons. However, it is not known exactly which genes
are expressed in what types of neurons, where, or when. Here, Chiu et al. used a technique called flow cytometry using different fluorescent
markers to isolate a group of cells called Dorsal Root Ganglion (DRG) neurons in
mice. These neurons have long thread-like fibers that extend from the spinal cord to
the skin, muscles and joints all over the body. These fibers carry sensory
information to the spinal cord, where it can be relayed to the brain and processed.
The experiments compared three distinct types of DRG neuron and found that they
differed in their ability to send information to other cells. Chiu et al. analyzed the expression of all the genes in the three types of DRG
neurons. Each type of neuron had distinct groups of genes that were being expressed.
Also, several genes that are known to be important for sensation were expressed at
different levels in the different types of cells. Next, large numbers of single cells
were analyzed to find out the finer details about the three types of neuron. These
findings made it possible to further divide the DRG neurons into six distinct subsets
that matched previously known groups of somatosensory neurons, and also identified
new ones. Chiu et al.'s findings reveal the complexity and diversity of the neurons involved in
carrying information about sensations towards the brain. This is an important step in
classifying the nervous system, and uncovers many genes previously not linked to
sensation. The next challenges lie in understanding how the expression of these genes
in each type of neuron relates to their unique roles. DOI:http://dx.doi.org/10.7554/eLife.04660.002
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Affiliation(s)
- Isaac M Chiu
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Lee B Barrett
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Erika K Williams
- Department of Cell Biology, Harvard Medical School, Boston, United States
| | - David E Strochlic
- Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Seungkyu Lee
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Andy D Weyer
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, United States
| | - Shan Lou
- Dana-Farber Cancer Institute, Harvard Medical School, Boston, United States
| | - Gregory S Bryman
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - David P Roberson
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Nader Ghasemlou
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Cara Piccoli
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Ezgi Ahat
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Victor Wang
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Enrique J Cobos
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
| | - Cheryl L Stucky
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, United States
| | - Qiufu Ma
- Dana-Farber Cancer Institute, Harvard Medical School, Boston, United States
| | - Stephen D Liberles
- Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Clifford J Woolf
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, United States
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Niu J, Vysochan A, Luo W. Dual innervation of neonatal Merkel cells in mouse touch domes. PLoS One 2014; 9:e92027. [PMID: 24637732 PMCID: PMC3956869 DOI: 10.1371/journal.pone.0092027] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Accepted: 02/19/2014] [Indexed: 12/17/2022] Open
Abstract
Merkel cell-neurite complexes are specialized mechanosensory end organs that mediate discriminative touch sensation. It is well established that type I slowly adapting (SAI) mechanoreceptors, which express neural filament heavy chain (NFH), innervate Merkel cells. It was previously shown that neurotrophic factor NT3 and its receptor TrkC play crucial roles in controlling touch dome Merkel cell innervation of NFH+ fibers. In addition, nerve fibers expressing another neurotrophic tyrosine receptor kinase (NTRK), Ret, innervate touch dome Merkel cells as well. However, the relationship between afferents responsive to NT3/TrkC signaling and those expressing Ret is unclear. It is also controversial if these Ret+ fibers belong to the early or late Ret+ DRG neurons, which are defined based on the co-expression and developmental dependence of TrkA. To address these questions, we genetically traced Ret+ and TrkC+ fibers and analyzed their developmental dependence on TrkA. We found that Merkel cells in neonatal mouse touch domes receive innervation of two types of fibers: one group is Ret+, while the other subset expresses TrkC and NFH. In addition, Ret+ fibers depend on TrkA for their survival and normal innervation whereas NFH+ Merkel cell innervating fibers are almost unaltered in TrkA mutant mice, supporting that Ret+ and NFH+/TrkC+ afferents are two distinct groups. Ret signaling, on the other hand, plays a minor role for the innervation of neonatal touch domes. In contrast, Merkel cells in the glabrous skin are mainly contacted by NFH+/TrkC+ afferents. Taken together, our results suggest that neonatal Merkel cells around hair follicles receive dual innervation while Merkel cells in the glabrous skin are mainly innervated by only SAI mechanoreceptors. In addition, our results suggest that neonatal Ret+ Merkel cell innervating fibers most likely belong to the late but not early Ret+ DRG neurons.
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Affiliation(s)
- Jingwen Niu
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Anna Vysochan
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Wenqin Luo
- Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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10
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Neurotrophin signalling and transcription programmes interactions in the development of somatosensory neurons. Handb Exp Pharmacol 2014; 220:329-53. [PMID: 24668479 DOI: 10.1007/978-3-642-45106-5_13] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Somatosensory neurons of the dorsal root ganglia are generated from multipotent neural crest cells by a process of progressive specification and differentiation. Intrinsic transcription programmes active in somatosensory neuron progenitors and early post-mitotic neurons drive the cell-type expression of neurotrophin receptors. In turn, signalling by members of the neurotrophin family controls expression of transcription factors that regulate neuronal sub-type specification. This chapter explores the mechanisms by which this crosstalk between neurotrophin signalling and transcription programmes generates the diverse functional sub-types of somatosensory neurons found in the mature animal.
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de Nooij JC, Doobar S, Jessell TM. Etv1 inactivation reveals proprioceptor subclasses that reflect the level of NT3 expression in muscle targets. Neuron 2013; 77:1055-68. [PMID: 23522042 DOI: 10.1016/j.neuron.2013.01.015] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/02/2013] [Indexed: 01/12/2023]
Abstract
The organization of spinal reflex circuits relies on the specification of distinct classes of proprioceptive sensory neurons (pSN), but the factors that drive such diversity remain unclear. We report here that pSNs supplying distinct skeletal muscles differ in their dependence on the ETS transcription factor Etv1 for their survival and differentiation. The status of Etv1-dependence is linked to the location of proprioceptor muscle targets: pSNs innervating hypaxial and axial muscles depend critically on Etv1 for survival, whereas those innervating certain limb muscles are resistant to Etv1 inactivation. The level of NT3 expression in individual muscles correlates with Etv1-dependence and the loss of pSNs triggered by Etv1 inactivation can be prevented by elevating the level of muscle-derived NT3-revealing a TrkC-activated Etv1-bypass pathway. Our findings support a model in which the specification of aspects of pSN subtype character is controlled by variation in the level of muscle NT3 expression and signaling.
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Affiliation(s)
- Joriene C de Nooij
- Department of Neuroscience, Howard Hughes Medical Institute, Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA
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