1
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Hoagland A, Schultz R, Cai Z, Newman ZL, Isacoff EY. Behavioral resilience via dynamic circuit firing homeostasis. Proc Natl Acad Sci U S A 2025; 122:e2421386122. [PMID: 40299703 PMCID: PMC12067288 DOI: 10.1073/pnas.2421386122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2024] [Accepted: 03/22/2025] [Indexed: 05/01/2025] Open
Abstract
Homeostatic regulation ensures stable neural circuit output under changing conditions. We find that in Drosophila larvae, either presynaptic weakening due to perturbation of transmitter release or postsynaptic weakening due to perturbation of glutamate receptors at synapses between motor neuron (MN) and muscle has little impact on locomotion, suggesting a nonsynaptic compensatory mechanism. In vivo imaging shows that five different forms of synaptic weakening increase the duration of activity bouts in type I MNs. Strikingly, this compensation is input selective: occurring only in the tonic type Ib MN, not the phasic type Is MN that innervates the same muscle. Moreover, an inhibitory class of central pre-MNs that innervates the tonic-but not phasic-input decreases in activity. The adjustment in activity occurs remarkably quickly: within minutes of synapse perturbation. We propose that MN firing is dynamically regulated by two coordinated mechanisms: a cell-autonomous adjustment of MN excitability and a circuit adjustment of inhibitory central drive. The input selectivity of this process suggests homeostatic adjustment to maintain tonic drive but hold constant the phasic drive that organizes locomotory wave patterns.
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Affiliation(s)
- Adam Hoagland
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA94720
| | - Ryan Schultz
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA94720
| | - Zerong Cai
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA94720
| | - Zachary L. Newman
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA94720
| | - Ehud Y. Isacoff
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA94720
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA94720
- Department of Neuroscience, University of California Berkeley, Berkeley, CA94720
- Weill Neurohub, University of California Berkeley, Berkeley, CA94720
- Molecular Biophysics and Integrated BioImaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA94720
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2
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Wang T, Frank CA. Using Electrophysiology to Study Homeostatic Plasticity at the Drosophila Neuromuscular Junction. Cold Spring Harb Protoc 2025; 2025:pdb.top108393. [PMID: 38688539 PMCID: PMC11522024 DOI: 10.1101/pdb.top108393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2024]
Abstract
The Drosophila melanogaster neuromuscular junction (NMJ) is a superb system for studying synapse function. Beyond that, the NMJ is also great for studying forms of synaptic plasticity. Over the last 25 years, Drosophila NMJ neuroscientists have pioneered understanding of a form of plasticity called homeostatic synaptic plasticity, which imparts functional stability on synaptic connections. The reason is straightforward: The NMJ has a robust capacity for stability. Moreover, many strategies that the NMJ uses to maintain appropriate levels of function are mirrored at other metazoan synapses. Here, we introduce core approaches that neurophysiologists use to study homeostatic synaptic plasticity at the peripheral Drosophila NMJ. We focus on methods to study a specific form of homeostatic plasticity termed presynaptic homeostatic potentiation (PHP), which is the most well-characterized one. Other forms such as presynaptic homeostatic depression and developmental forms of homeostasis are briefly discussed. Finally, we share lists of several dozen factors and conditions known to influence the execution of PHP.
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Affiliation(s)
- Tingting Wang
- Department of Pharmacology and Physiology, Georgetown University Medical Center, Washington, D.C. 20007, USA
| | - C Andrew Frank
- Department of Anatomy and Cell Biology, Iowa Neuroscience Institute, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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3
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Chien C, He K, Perry S, Tchitchkan E, Han Y, Li X, Dickman D. Distinct input-specific mechanisms enable presynaptic homeostatic plasticity. SCIENCE ADVANCES 2025; 11:eadr0262. [PMID: 39951523 PMCID: PMC11827636 DOI: 10.1126/sciadv.adr0262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2024] [Accepted: 01/15/2025] [Indexed: 02/16/2025]
Abstract
Synapses are endowed with the flexibility to change through experience, but must be sufficiently stable to last a lifetime. This tension is illustrated at the Drosophila neuromuscular junction (NMJ), where two motor inputs that differ in structural and functional properties coinnervate most muscles to coordinate locomotion. To stabilize NMJ activity, motor neurons augment neurotransmitter release following diminished postsynaptic glutamate receptor functionality, termed presynaptic homeostatic potentiation (PHP). How these distinct inputs contribute to PHP plasticity remains enigmatic. We have used a botulinum neurotoxin to selectively silence each input and resolve their roles in PHP, demonstrating that PHP is input specific: Chronic (genetic) PHP selectively targets the tonic MN-Ib, where active zone remodeling enhances Ca2+ influx to promote increased glutamate release. In contrast, acute (pharmacological) PHP selectively increases vesicle pools to potentiate phasic MN-Is. Thus, distinct homeostatic modulations in active zone nanoarchitecture, vesicle pools, and Ca2+ influx collaborate to enable input-specific PHP expression.
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Affiliation(s)
- Chun Chien
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
- USC Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA
| | - Kaikai He
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
- USC Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA
| | - Sarah Perry
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
| | - Elizabeth Tchitchkan
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
| | - Yifu Han
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
- USC Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA
| | - Xiling Li
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
- USC Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA
| | - Dion Dickman
- Department of Neurobiology, University of Southern California, Los Angeles, CA, USA
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4
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Medeiros AT, Gratz SJ, Delgado A, Ritt JT, O'Connor-Giles KM. Ca 2+ channel and active zone protein abundance intersects with input-specific synapse organization to shape functional synaptic diversity. eLife 2024; 12:RP88412. [PMID: 39291956 PMCID: PMC11410372 DOI: 10.7554/elife.88412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/19/2024] Open
Abstract
Synaptic heterogeneity is a hallmark of nervous systems that enables complex and adaptable communication in neural circuits. To understand circuit function, it is thus critical to determine the factors that contribute to the functional diversity of synapses. We investigated the contributions of voltage-gated calcium channel (VGCC) abundance, spatial organization, and subunit composition to synapse diversity among and between synapses formed by two closely related Drosophila glutamatergic motor neurons with distinct neurotransmitter release probabilities (Pr). Surprisingly, VGCC levels are highly predictive of heterogeneous Pr among individual synapses of either low- or high-Pr inputs, but not between inputs. We find that the same number of VGCCs are more densely organized at high-Pr synapses, consistent with tighter VGCC-synaptic vesicle coupling. We generated endogenously tagged lines to investigate VGCC subunits in vivo and found that the α2δ-3 subunit Straightjacket along with the CAST/ELKS active zone (AZ) protein Bruchpilot, both key regulators of VGCCs, are less abundant at high-Pr inputs, yet positively correlate with Pr among synapses formed by either input. Consistently, both Straightjacket and Bruchpilot levels are dynamically increased across AZs of both inputs when neurotransmitter release is potentiated to maintain stable communication following glutamate receptor inhibition. Together, these findings suggest a model in which VGCC and AZ protein abundance intersects with input-specific spatial and molecular organization to shape the functional diversity of synapses.
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Affiliation(s)
- Audrey T Medeiros
- Neuroscience Graduate Training Program, Brown University, Providence, United States
| | - Scott J Gratz
- Department of Neuroscience, Brown University, Providence, United States
| | - Ambar Delgado
- Department of Neuroscience, Brown University, Providence, United States
| | - Jason T Ritt
- Department of Neuroscience, Brown University, Providence, United States
- Carney Institute for Brain Science, Brown University, Providence, United States
| | - Kate M O'Connor-Giles
- Neuroscience Graduate Training Program, Brown University, Providence, United States
- Department of Neuroscience, Brown University, Providence, United States
- Carney Institute for Brain Science, Brown University, Providence, United States
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5
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Chien C, He K, Perry S, Tchitchkan E, Han Y, Li X, Dickman D. Distinct input-specific mechanisms enable presynaptic homeostatic plasticity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.09.10.612361. [PMID: 39314403 PMCID: PMC11419068 DOI: 10.1101/2024.09.10.612361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 09/25/2024]
Abstract
Synapses are endowed with the flexibility to change through experience, but must be sufficiently stable to last a lifetime. This tension is illustrated at the Drosophila neuromuscular junction (NMJ), where two motor inputs that differ in structural and functional properties co-innervate most muscles to coordinate locomotion. To stabilize NMJ activity, motor neurons augment neurotransmitter release following diminished postsynaptic glutamate receptor functionality, termed presynaptic homeostatic potentiation (PHP). How these distinct inputs contribute to PHP plasticity remains enigmatic. We have used a botulinum neurotoxin to selectively silence each input and resolve their roles in PHP, demonstrating that PHP is input-specific: Chronic (genetic) PHP selectively targets the tonic MN-Ib, where active zone remodeling enhances Ca2+ influx to promote increased glutamate release. In contrast, acute (pharmacological) PHP selectively increases vesicle pools to potentiate phasic MN-Is. Thus, distinct homeostatic modulations in active zone nanoarchitecture, vesicle pools, and Ca2+ influx collaborate to enable input-specific PHP expression.
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Affiliation(s)
- Chun Chien
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
- USC Neuroscience Graduate Program
| | - Kaikai He
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
- USC Neuroscience Graduate Program
| | - Sarah Perry
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
| | - Elizabeth Tchitchkan
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
| | - Yifu Han
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
- USC Neuroscience Graduate Program
| | - Xiling Li
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
- USC Neuroscience Graduate Program
| | - Dion Dickman
- University of Southern California, Department of Neurobiology, Los Angeles, CA USA
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6
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Medeiros AT, Gratz S, Delgado A, Ritt J, O’Connor-Giles KM. Ca 2+ channel and active zone protein abundance intersects with input-specific synapse organization to shape functional synaptic diversity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.04.02.535290. [PMID: 37034654 PMCID: PMC10081318 DOI: 10.1101/2023.04.02.535290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
Abstract
Synaptic heterogeneity is a hallmark of nervous systems that enables complex and adaptable communication in neural circuits. To understand circuit function, it is thus critical to determine the factors that contribute to the functional diversity of synapses. We investigated the contributions of voltage-gated calcium channel (VGCC) abundance, spatial organization, and subunit composition to synapse diversity among and between synapses formed by two closely related Drosophila glutamatergic motor neurons with distinct neurotransmitter release probabilities (Pr). Surprisingly, VGCC levels are highly predictive of heterogeneous Pr among individual synapses of either low- or high-Pr inputs, but not between inputs. We find that the same number of VGCCs are more densely organized at high-Pr synapses, consistent with tighter VGCC-synaptic vesicle coupling. We generated endogenously tagged lines to investigate VGCC subunits in vivo and found that the α2δ-3 subunit Straightjacket along with the CAST/ELKS active zone (AZ) protein Bruchpilot, both key regulators of VGCCs, are less abundant at high-Pr inputs, yet positively correlate with Pr among synapses formed by either input. Consistently, both Straightjacket and Bruchpilot levels are dynamically increased across AZs of both inputs when neurotransmitter release is potentiated to maintain stable communication following glutamate receptor inhibition. Together, these findings suggest a model in which VGCC and AZ protein abundance intersects with input-specific spatial and molecular organization to shape the functional diversity of synapses.
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Affiliation(s)
- A. T. Medeiros
- Neuroscience Graduate Training Program, Brown University, Providence, RI
| | - S.J. Gratz
- Department of Neuroscience, Brown University, Providence, RI
| | - A. Delgado
- Department of Neuroscience, Brown University, Providence, RI
| | - J.T. Ritt
- Department of Neuroscience, Brown University, Providence, RI
- Carney Institute for Brain Science, Brown University, Providence, RI
| | - Kate M. O’Connor-Giles
- Neuroscience Graduate Training Program, Brown University, Providence, RI
- Department of Neuroscience, Brown University, Providence, RI
- Carney Institute for Brain Science, Brown University, Providence, RI
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7
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Crane AB, Jetti SK, Littleton JT. A stochastic RNA editing process targets a limited number of sites in individual Drosophila glutamatergic motoneurons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.17.594696. [PMID: 38798345 PMCID: PMC11118563 DOI: 10.1101/2024.05.17.594696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
RNA editing is a post-transcriptional source of protein diversity and occurs across the animal kingdom. Given the complete profile of mRNA targets and their editing rate in individual cells is unclear, we analyzed single cell RNA transcriptomes from Drosophila larval tonic and phasic glutamatergic motoneuron subtypes to determine the most highly edited targets and identify cell-type specific editing. From ∼15,000 genes encoded in the genome, 316 high confidence A-to-I canonical RNA edit sites were identified, with 102 causing missense amino acid changes in proteins regulating membrane excitability, synaptic transmission, and cellular function. Some sites showed 100% editing in single neurons as observed with mRNAs encoding mammalian AMPA receptors. However, most sites were edited at lower levels and generated variable expression of edited and unedited mRNAs within individual neurons. Together, these data provide insights into how the RNA editing landscape alters protein function to modulate the properties of two well-characterized neuronal populations in Drosophila .
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8
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Jetti SK, Crane AB, Akbergenova Y, Aponte-Santiago NA, Cunningham KL, Whittaker CA, Littleton JT. Molecular logic of synaptic diversity between Drosophila tonic and phasic motoneurons. Neuron 2023; 111:3554-3569.e7. [PMID: 37611584 DOI: 10.1016/j.neuron.2023.07.019] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 05/22/2023] [Accepted: 07/28/2023] [Indexed: 08/25/2023]
Abstract
Although neuronal subtypes display unique synaptic organization and function, the underlying transcriptional differences that establish these features are poorly understood. To identify molecular pathways that contribute to synaptic diversity, single-neuron Patch-seq RNA profiling was performed on Drosophila tonic and phasic glutamatergic motoneurons. Tonic motoneurons form weaker facilitating synapses onto single muscles, while phasic motoneurons form stronger depressing synapses onto multiple muscles. Super-resolution microscopy and in vivo imaging demonstrated that synaptic active zones in phasic motoneurons are more compact and display enhanced Ca2+ influx compared with their tonic counterparts. Genetic analysis identified unique synaptic properties that mapped onto gene expression differences for several cellular pathways, including distinct signaling ligands, post-translational modifications, and intracellular Ca2+ buffers. These findings provide insights into how unique transcriptomes drive functional and morphological differences between neuronal subtypes.
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Affiliation(s)
- Suresh K Jetti
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Andrés B Crane
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Nicole A Aponte-Santiago
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Karen L Cunningham
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Charles A Whittaker
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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9
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He K, Han Y, Li X, Hernandez RX, Riboul DV, Feghhi T, Justs KA, Mahneva O, Perry S, Macleod GT, Dickman D. Physiologic and Nanoscale Distinctions Define Glutamatergic Synapses in Tonic vs Phasic Neurons. J Neurosci 2023; 43:4598-4611. [PMID: 37221096 PMCID: PMC10286941 DOI: 10.1523/jneurosci.0046-23.2023] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 05/05/2023] [Accepted: 05/11/2023] [Indexed: 05/25/2023] Open
Abstract
Neurons exhibit a striking degree of functional diversity, each one tuned to the needs of the circuitry in which it is embedded. A fundamental functional dichotomy occurs in activity patterns, with some neurons firing at a relatively constant "tonic" rate, while others fire in bursts, a "phasic" pattern. Synapses formed by tonic versus phasic neurons are also functionally differentiated, yet the bases of their distinctive properties remain enigmatic. A major challenge toward illuminating the synaptic differences between tonic and phasic neurons is the difficulty in isolating their physiological properties. At the Drosophila neuromuscular junction, most muscle fibers are coinnervated by two motor neurons: the tonic "MN-Ib" and phasic "MN-Is." Here, we used selective expression of a newly developed botulinum neurotoxin transgene to silence tonic or phasic motor neurons in Drosophila larvae of either sex. This approach highlighted major differences in their neurotransmitter release properties, including probability, short-term plasticity, and vesicle pools. Furthermore, Ca2+ imaging demonstrated ∼2-fold greater Ca2+ influx at phasic neuron release sites relative to tonic, along with an enhanced synaptic vesicle coupling. Finally, confocal and super-resolution imaging revealed that phasic neuron release sites are organized in a more compact arrangement, with enhanced stoichiometry of voltage-gated Ca2+ channels relative to other active zone scaffolds. These data suggest that distinctions in active zone nano-architecture and Ca2+ influx collaborate to differentially tune glutamate release at tonic versus phasic synaptic subtypes.SIGNIFICANCE STATEMENT "Tonic" and "phasic" neuronal subtypes, based on differential firing properties, are common across many nervous systems. Using a recently developed approach to selectively silence transmission from one of these two neurons, we reveal specialized synaptic functional and structural properties that distinguish these specialized neurons. This study provides important insights into how input-specific synaptic diversity is achieved, which could have implications for neurologic disorders that involve changes in synaptic function.
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Affiliation(s)
- Kaikai He
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
- USC Neuroscience Graduate Program, Los Angeles, California 90089
| | - Yifu Han
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
- USC Neuroscience Graduate Program, Los Angeles, California 90089
| | - Xiling Li
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
- USC Neuroscience Graduate Program, Los Angeles, California 90089
| | - Roberto X Hernandez
- Integrative Biology and Neuroscience Graduate Program, Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
- International Max Planck Research School for Brain and Behavior, Jupiter, Florida 33458
| | - Danielle V Riboul
- Integrative Biology Graduate Program, Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
| | - Touhid Feghhi
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431
| | - Karlis A Justs
- Integrative Biology and Neuroscience Graduate Program, Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
| | - Olena Mahneva
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida 33458
| | - Sarah Perry
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
| | - Gregory T Macleod
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida 33458
- Institute for Human Health and Disease Intervention, Florida Atlantic University, Jupiter, Florida 33458
| | - Dion Dickman
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
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10
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Jetti SK, Crane AB, Akbergenova Y, Aponte-Santiago NA, Cunningham KL, Whittaker CA, Littleton JT. Molecular Logic of Synaptic Diversity Between Drosophila Tonic and Phasic Motoneurons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.17.524447. [PMID: 36711745 PMCID: PMC9882338 DOI: 10.1101/2023.01.17.524447] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Although neuronal subtypes display unique synaptic organization and function, the underlying transcriptional differences that establish these features is poorly understood. To identify molecular pathways that contribute to synaptic diversity, single neuron PatchSeq RNA profiling was performed on Drosophila tonic and phasic glutamatergic motoneurons. Tonic motoneurons form weaker facilitating synapses onto single muscles, while phasic motoneurons form stronger depressing synapses onto multiple muscles. Super-resolution microscopy and in vivo imaging demonstrated synaptic active zones in phasic motoneurons are more compact and display enhanced Ca 2+ influx compared to their tonic counterparts. Genetic analysis identified unique synaptic properties that mapped onto gene expression differences for several cellular pathways, including distinct signaling ligands, post-translational modifications and intracellular Ca 2+ buffers. These findings provide insights into how unique transcriptomes drive functional and morphological differences between neuronal subtypes.
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Affiliation(s)
- Suresh K Jetti
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
| | - Andrés B Crane
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
| | - Nicole A Aponte-Santiago
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
| | - Karen L Cunningham
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
| | - Charles A Whittaker
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
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11
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KASAI H. Unraveling the mysteries of dendritic spine dynamics: Five key principles shaping memory and cognition. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2023; 99:254-305. [PMID: 37821392 PMCID: PMC10749395 DOI: 10.2183/pjab.99.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/13/2023] [Accepted: 07/11/2023] [Indexed: 10/13/2023]
Abstract
Recent research extends our understanding of brain processes beyond just action potentials and chemical transmissions within neural circuits, emphasizing the mechanical forces generated by excitatory synapses on dendritic spines to modulate presynaptic function. From in vivo and in vitro studies, we outline five central principles of synaptic mechanics in brain function: P1: Stability - Underpinning the integral relationship between the structure and function of the spine synapses. P2: Extrinsic dynamics - Highlighting synapse-selective structural plasticity which plays a crucial role in Hebbian associative learning, distinct from pathway-selective long-term potentiation (LTP) and depression (LTD). P3: Neuromodulation - Analyzing the role of G-protein-coupled receptors, particularly dopamine receptors, in time-sensitive modulation of associative learning frameworks such as Pavlovian classical conditioning and Thorndike's reinforcement learning (RL). P4: Instability - Addressing the intrinsic dynamics crucial to memory management during continual learning, spotlighting their role in "spine dysgenesis" associated with mental disorders. P5: Mechanics - Exploring how synaptic mechanics influence both sides of synapses to establish structural traces of short- and long-term memory, thereby aiding the integration of mental functions. We also delve into the historical background and foresee impending challenges.
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Affiliation(s)
- Haruo KASAI
- International Research Center for Neurointelligence (WPI-IRCN), UTIAS, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
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12
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Orr BO, Fetter RD, Davis GW. Activation and expansion of presynaptic signaling foci drives presynaptic homeostatic plasticity. Neuron 2022; 110:3743-3759.e6. [PMID: 36087584 PMCID: PMC9671843 DOI: 10.1016/j.neuron.2022.08.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 06/07/2022] [Accepted: 08/11/2022] [Indexed: 12/15/2022]
Abstract
Presynaptic homeostatic plasticity (PHP) adaptively regulates synaptic transmission in health and disease. Despite identification of numerous genes that are essential for PHP, we lack a dynamic framework to explain how PHP is initiated, potentiated, and limited to achieve precise control of vesicle fusion. Here, utilizing both mice and Drosophila, we demonstrate that PHP progresses through the assembly and physical expansion of presynaptic signaling foci where activated integrins biochemically converge with trans-synaptic Semaphorin2b/PlexinB signaling. Each component of the identified signaling complexes, including alpha/beta-integrin, Semaphorin2b, PlexinB, talin, and focal adhesion kinase (FAK), and their biochemical interactions, are essential for PHP. Complex integrity requires the Sema2b ligand and complex expansion includes a ∼2.5-fold expansion of active-zone associated puncta composed of the actin-binding protein talin. Finally, complex pre-expansion is sufficient to accelerate the rate and extent of PHP. A working model is proposed incorporating signal convergence with dynamic molecular assemblies that instruct PHP.
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Affiliation(s)
- Brian O Orr
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158 USA
| | - Richard D Fetter
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158 USA
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158 USA.
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13
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Han Y, Chien C, Goel P, He K, Pinales C, Buser C, Dickman D. Botulinum neurotoxin accurately separates tonic vs. phasic transmission and reveals heterosynaptic plasticity rules in Drosophila. eLife 2022; 11:e77924. [PMID: 35993544 PMCID: PMC9439677 DOI: 10.7554/elife.77924] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 08/20/2022] [Indexed: 11/13/2022] Open
Abstract
In developing and mature nervous systems, diverse neuronal subtypes innervate common targets to establish, maintain, and modify neural circuit function. A major challenge towards understanding the structural and functional architecture of neural circuits is to separate these inputs and determine their intrinsic and heterosynaptic relationships. The Drosophila larval neuromuscular junction is a powerful model system to study these questions, where two glutamatergic motor neurons, the strong phasic-like Is and weak tonic-like Ib, co-innervate individual muscle targets to coordinate locomotor behavior. However, complete neurotransmission from each input has never been electrophysiologically separated. We have employed a botulinum neurotoxin, BoNT-C, that eliminates both spontaneous and evoked neurotransmission without perturbing synaptic growth or structure, enabling the first approach that accurately isolates input-specific neurotransmission. Selective expression of BoNT-C in Is or Ib motor neurons disambiguates the functional properties of each input. Importantly, the blended values of Is+Ib neurotransmission can be fully recapitulated by isolated physiology from each input. Finally, selective silencing by BoNT-C does not induce heterosynaptic structural or functional plasticity at the convergent input. Thus, BoNT-C establishes the first approach to accurately separate neurotransmission between tonic vs. phasic neurons and defines heterosynaptic plasticity rules in a powerful model glutamatergic circuit.
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Affiliation(s)
- Yifu Han
- Department of Neurobiology, University of Southern CaliforniaLos AngelesUnited States
| | - Chun Chien
- Department of Neurobiology, University of Southern CaliforniaLos AngelesUnited States
| | - Pragya Goel
- Department of Neurobiology, University of Southern CaliforniaLos AngelesUnited States
| | - Kaikai He
- Department of Neurobiology, University of Southern CaliforniaLos AngelesUnited States
| | | | | | - Dion Dickman
- Department of Neurobiology, University of Southern CaliforniaLos AngelesUnited States
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14
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Wenner PA, Pekala D. Homeostatic Regulation of Motoneuron Properties in Development. ADVANCES IN NEUROBIOLOGY 2022; 28:87-107. [PMID: 36066822 DOI: 10.1007/978-3-031-07167-6_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Homeostatic plasticity represents a set of compensatory mechanisms that are engaged following a perturbation to some feature of neuronal or network function. Homeostatic mechanisms are most robustly expressed during development, a period that is replete with various perturbations such as increased cell size and the addition/removal of synaptic connections. In this review we look at numerous studies that have advanced our understanding of homeostatic plasticity by taking advantage of the accessibility of developing motoneurons. We discuss the homeostatic regulation of embryonic movements in the living chick embryo and describe the spinal compensatory mechanisms that act to recover these movements (homeostatic intrinsic plasticity) or stabilize synaptic strength (synaptic scaling). We describe the expression and triggering mechanisms of these forms of homeostatic plasticity and thereby gain an understanding of their roles in the motor system. We then illustrate how these findings can be extended to studies of developing motoneurons in other systems including the rodents, zebrafish, and fly. Furthermore, studies in developing drosophila have been critical in identifying some of the molecular signaling cascades and expression mechanisms that underlie homeostatic intrinsic membrane excitability. This powerful model organism has also been used to study a presynaptic form of homeostatic plasticity where increases or decreases in synaptic transmission are associated with compensatory changes in probability of release at the neuromuscular junction. Further, we describe studies that demonstrate homeostatic adjustments of ion channel expression following perturbations to other kinds of ion channels. Finally, we discuss work in xenopus that shows a homeostatic regulation of neurotransmitter phenotype in developing motoneurons following activity perturbations. Together, this work illustrates the importance of developing motoneurons in elucidating the mechanisms and roles of homeostatic plasticity.
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Affiliation(s)
- Peter A Wenner
- Department of Cell Biology, Whitehead Biomedical Research Building, Emory University School of Medicine, Atlanta, GA, USA.
| | - Dobromila Pekala
- Department of Cell Biology, Whitehead Biomedical Research Building, Emory University School of Medicine, Atlanta, GA, USA
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15
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Sauvola CW, Akbergenova Y, Cunningham KL, Aponte-Santiago NA, Littleton JT. The decoy SNARE Tomosyn sets tonic versus phasic release properties and is required for homeostatic synaptic plasticity. eLife 2021; 10:e72841. [PMID: 34713802 PMCID: PMC8612732 DOI: 10.7554/elife.72841] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 10/27/2021] [Indexed: 12/14/2022] Open
Abstract
Synaptic vesicle (SV) release probability (Pr) is a key presynaptic determinant of synaptic strength established by cell-intrinsic properties and further refined by plasticity. To characterize mechanisms that generate Pr heterogeneity between distinct neuronal populations, we examined glutamatergic tonic (Ib) and phasic (Is) motoneurons in Drosophila with stereotyped differences in Pr and synaptic plasticity. We found the decoy soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) Tomosyn is differentially expressed between these motoneuron subclasses and contributes to intrinsic differences in their synaptic output. Tomosyn expression enables tonic release in Ib motoneurons by reducing SNARE complex formation and suppressing Pr to generate decreased levels of SV fusion and enhanced resistance to synaptic fatigue. In contrast, phasic release dominates when Tomosyn expression is low, enabling high intrinsic Pr at Is terminals at the expense of sustained release and robust presynaptic potentiation. In addition, loss of Tomosyn disrupts the ability of tonic synapses to undergo presynaptic homeostatic potentiation.
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Affiliation(s)
- Chad W Sauvola
- Department of Brain and Cognitive Sciences, The Picower Institute of Learning and Memory, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Yulia Akbergenova
- Department of Brain and Cognitive Sciences, The Picower Institute of Learning and Memory, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Karen L Cunningham
- Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
| | | | - J Troy Littleton
- Department of Brain and Cognitive Sciences, The Picower Institute of Learning and Memory, Massachusetts Institute of TechnologyCambridgeUnited States
- Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
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16
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Mrestani A, Pauli M, Kollmannsberger P, Repp F, Kittel RJ, Eilers J, Doose S, Sauer M, Sirén AL, Heckmann M, Paul MM. Active zone compaction correlates with presynaptic homeostatic potentiation. Cell Rep 2021; 37:109770. [PMID: 34610300 DOI: 10.1016/j.celrep.2021.109770] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 05/14/2021] [Accepted: 09/07/2021] [Indexed: 12/30/2022] Open
Abstract
Neurotransmitter release is stabilized by homeostatic plasticity. Presynaptic homeostatic potentiation (PHP) operates on timescales ranging from minute- to life-long adaptations and likely involves reorganization of presynaptic active zones (AZs). At Drosophila melanogaster neuromuscular junctions, earlier work ascribed AZ enlargement by incorporating more Bruchpilot (Brp) scaffold protein a role in PHP. We use localization microscopy (direct stochastic optical reconstruction microscopy [dSTORM]) and hierarchical density-based spatial clustering of applications with noise (HDBSCAN) to study AZ plasticity during PHP at the synaptic mesoscale. We find compaction of individual AZs in acute philanthotoxin-induced and chronic genetically induced PHP but unchanged copy numbers of AZ proteins. Compaction even occurs at the level of Brp subclusters, which move toward AZ centers, and in Rab3 interacting molecule (RIM)-binding protein (RBP) subclusters. Furthermore, correlative confocal and dSTORM imaging reveals how AZ compaction in PHP translates into apparent increases in AZ area and Brp protein content, as implied earlier.
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Affiliation(s)
- Achmed Mrestani
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Neurology, Leipzig University Medical Center, 04103 Leipzig, Germany
| | - Martin Pauli
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Neurosurgery, University Hospital of Würzburg, 97080 Würzburg, Germany
| | - Philip Kollmannsberger
- Center for Computational and Theoretical Biology, Julius Maximilians University Würzburg, 97074 Würzburg, Germany
| | - Felix Repp
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Center for Computational and Theoretical Biology, Julius Maximilians University Würzburg, 97074 Würzburg, Germany; Department of Neurosurgery, University Hospital of Würzburg, 97080 Würzburg, Germany
| | - Robert J Kittel
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Institute of Biology, Department of Animal Physiology, Leipzig University, 04103 Leipzig, Germany; Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - Sören Doose
- Department of Biotechnology and Biophysics, Julius Maximilians University Würzburg, 97074 Würzburg, Germany
| | - Markus Sauer
- Department of Biotechnology and Biophysics, Julius Maximilians University Würzburg, 97074 Würzburg, Germany
| | - Anna-Leena Sirén
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Neurosurgery, University Hospital of Würzburg, 97080 Würzburg, Germany
| | - Manfred Heckmann
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany.
| | - Mila M Paul
- Institute for Physiology, Department of Neurophysiology, Julius Maximilians University Würzburg, 97070 Würzburg, Germany; Department of Orthopaedic Trauma, Hand, Plastic and Reconstructive Surgery, University Hospital of Würzburg, 97080 Würzburg, Germany.
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17
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Lim WK, Kaur P, Huang H, Jo RS, Ramamoorthy A, Ng LF, Suresh J, Maisha FI, Mathuru AS, Tolwinski NS. Optogenetic approaches for understanding homeostatic and degenerative processes in Drosophila. Cell Mol Life Sci 2021; 78:5865-5880. [PMID: 34232330 PMCID: PMC8260576 DOI: 10.1007/s00018-021-03836-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/22/2021] [Accepted: 04/08/2021] [Indexed: 12/18/2022]
Abstract
Many organs and tissues have an intrinsic ability to regenerate from a dedicated, tissue-specific stem cell pool. As organisms age, the process of self-regulation or homeostasis begins to slow down with fewer stem cells available for tissue repair. Tissues become more fragile and organs less efficient. This slowdown of homeostatic processes leads to the development of cellular and neurodegenerative diseases. In this review, we highlight the recent use and future potential of optogenetic approaches to study homeostasis. Optogenetics uses photosensitive molecules and genetic engineering to modulate cellular activity in vivo, allowing precise experiments with spatiotemporal control. We look at applications of this technology for understanding the mechanisms governing homeostasis and degeneration as applied to widely used model organisms, such as Drosophila melanogaster, where other common tools are less effective or unavailable.
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Affiliation(s)
- Wen Kin Lim
- Science Division, Yale-NUS College, Singapore, Singapore
| | - Prameet Kaur
- Science Division, Yale-NUS College, Singapore, Singapore
| | - Huanyan Huang
- Science Division, Yale-NUS College, Singapore, Singapore
| | | | | | - Li Fang Ng
- Science Division, Yale-NUS College, Singapore, Singapore
| | - Jahnavi Suresh
- Science Division, Yale-NUS College, Singapore, Singapore
| | | | - Ajay S Mathuru
- Science Division, Yale-NUS College, Singapore, Singapore
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18
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Goel P, Dickman D. Synaptic homeostats: latent plasticity revealed at the Drosophila neuromuscular junction. Cell Mol Life Sci 2021; 78:3159-3179. [PMID: 33449150 PMCID: PMC8044042 DOI: 10.1007/s00018-020-03732-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 11/19/2020] [Accepted: 12/04/2020] [Indexed: 12/11/2022]
Abstract
Homeostatic signaling systems are fundamental forms of biological regulation that maintain stable functionality in a changing environment. In the nervous system, synapses are crucial substrates for homeostatic modulation, serving to establish, maintain, and modify the balance of excitation and inhibition. Synapses must be sufficiently flexible to enable the plasticity required for learning and memory but also endowed with the stability to last a lifetime. In response to the processes of development, growth, remodeling, aging, and disease that challenge synapses, latent forms of adaptive plasticity become activated to maintain synaptic stability. In recent years, new insights into the homeostatic control of synaptic function have been achieved using the powerful Drosophila neuromuscular junction (NMJ). This review will focus on work over the past 10 years that has illuminated the cellular and molecular mechanisms of five homeostats that operate at the fly NMJ. These homeostats adapt to loss of postsynaptic neurotransmitter receptor functionality, glutamate imbalance, axonal injury, as well as aberrant synaptic growth and target innervation. These diverse homeostats work independently yet can be simultaneously expressed to balance neurotransmission. Growing evidence from this model glutamatergic synapse suggests these ancient homeostatic signaling systems emerged early in evolution and are fundamental forms of plasticity that also function to stabilize mammalian cholinergic NMJs and glutamatergic central synapses.
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Affiliation(s)
- Pragya Goel
- Department of Neurobiology, University of Southern California, Los Angeles, CA, 90089, USA
| | - Dion Dickman
- Department of Neurobiology, University of Southern California, Los Angeles, CA, 90089, USA.
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19
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Structural and Functional Synaptic Plasticity Induced by Convergent Synapse Loss in the Drosophila Neuromuscular Circuit. J Neurosci 2021; 41:1401-1417. [PMID: 33402422 DOI: 10.1523/jneurosci.1492-20.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 11/28/2020] [Accepted: 12/17/2020] [Indexed: 12/22/2022] Open
Abstract
Throughout the nervous system, the convergence of two or more presynaptic inputs on a target cell is commonly observed. The question we ask here is to what extent converging inputs influence each other's structural and functional synaptic plasticity. In complex circuits, isolating individual inputs is difficult because postsynaptic cells can receive thousands of inputs. An ideal model to address this question is the Drosophila larval neuromuscular junction (NMJ) where each postsynaptic muscle cell receives inputs from two glutamatergic types of motor neurons (MNs), known as 1b and 1s MNs. Notably, each muscle is unique and receives input from a different combination of 1b and 1s MNs; we surveyed multiple muscles for this reason. Here, we identified a cell-specific promoter that allows ablation of 1s MNs postinnervation and measured structural and functional responses of convergent 1b NMJs using microscopy and electrophysiology. For all muscles examined in both sexes, ablation of 1s MNs resulted in NMJ expansion and increased spontaneous neurotransmitter release at corresponding 1b NMJs. This demonstrates that 1b NMJs can compensate for the loss of convergent 1s MNs. However, only a subset of 1b NMJs showed compensatory evoked neurotransmission, suggesting target-specific plasticity. Silencing 1s MNs led to similar plasticity at 1b NMJs, suggesting that evoked neurotransmission from 1s MNs contributes to 1b synaptic plasticity. Finally, we genetically blocked 1s innervation in male larvae and robust 1b synaptic plasticity was eliminated, raising the possibility that 1s NMJ formation is required to set up a reference for subsequent synaptic perturbations.SIGNIFICANCE STATEMENT In complex neural circuits, multiple convergent inputs contribute to the activity of the target cell, but whether synaptic plasticity exists among these inputs has not been thoroughly explored. In this study, we examined synaptic plasticity in the structurally and functionally tractable Drosophila larval neuromuscular system. In this convergent circuit, each muscle is innervated by a unique pair of motor neurons. Removal of one neuron after innervation causes the adjacent neuron to increase neuromuscular junction outgrowth and functional output. However, this is not a general feature as each motor neuron differentially compensates. Further, robust compensation requires initial coinnervation by both neurons. Understanding how neurons respond to perturbations in adjacent neurons will provide insight into nervous system plasticity in both healthy and disease states.
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20
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Aponte-Santiago NA, Littleton JT. Synaptic Properties and Plasticity Mechanisms of Invertebrate Tonic and Phasic Neurons. Front Physiol 2020; 11:611982. [PMID: 33391026 PMCID: PMC7772194 DOI: 10.3389/fphys.2020.611982] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 11/24/2020] [Indexed: 12/15/2022] Open
Abstract
Defining neuronal cell types and their associated biophysical and synaptic diversity has become an important goal in neuroscience as a mechanism to create comprehensive brain cell atlases in the post-genomic age. Beyond broad classification such as neurotransmitter expression, interneuron vs. pyramidal, sensory or motor, the field is still in the early stages of understanding closely related cell types. In both vertebrate and invertebrate nervous systems, one well-described distinction related to firing characteristics and synaptic release properties are tonic and phasic neuronal subtypes. In vertebrates, these classes were defined based on sustained firing responses during stimulation (tonic) vs. transient responses that rapidly adapt (phasic). In crustaceans, the distinction expanded to include synaptic release properties, with tonic motoneurons displaying sustained firing and weaker synapses that undergo short-term facilitation to maintain muscle contraction and posture. In contrast, phasic motoneurons with stronger synapses showed rapid depression and were recruited for short bursts during fast locomotion. Tonic and phasic motoneurons with similarities to those in crustaceans have been characterized in Drosophila, allowing the genetic toolkit associated with this model to be used for dissecting the unique properties and plasticity mechanisms for these neuronal subtypes. This review outlines general properties of invertebrate tonic and phasic motoneurons and highlights recent advances that characterize distinct synaptic and plasticity pathways associated with two closely related glutamatergic neuronal cell types that drive invertebrate locomotion.
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Affiliation(s)
- Nicole A. Aponte-Santiago
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
- Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, San Francisco, CA, United States
| | - J. Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
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21
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Aponte-Santiago NA, Ormerod KG, Akbergenova Y, Littleton JT. Synaptic Plasticity Induced by Differential Manipulation of Tonic and Phasic Motoneurons in Drosophila. J Neurosci 2020; 40:6270-6288. [PMID: 32631939 PMCID: PMC7424871 DOI: 10.1523/jneurosci.0925-20.2020] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 06/22/2020] [Accepted: 06/28/2020] [Indexed: 12/12/2022] Open
Abstract
Structural and functional plasticity induced by neuronal competition is a common feature of developing nervous systems. However, the rules governing how postsynaptic cells differentiate between presynaptic inputs are unclear. In this study, we characterized synaptic interactions following manipulations of tonic Ib or phasic Is glutamatergic motoneurons that coinnervate postsynaptic muscles of male or female Drosophila melanogaster larvae. After identifying drivers for each neuronal subtype, we performed ablation or genetic manipulations to alter neuronal activity and examined the effects on synaptic innervation and function at neuromuscular junctions. Ablation of either Ib or Is resulted in decreased muscle response, with some functional compensation occurring in the Ib input when Is was missing. In contrast, the Is terminal failed to show functional or structural changes following loss of the coinnervating Ib input. Decreasing the activity of the Ib or Is neuron with tetanus toxin light chain resulted in structural changes in muscle innervation. Decreased Ib activity resulted in reduced active zone (AZ) number and decreased postsynaptic subsynaptic reticulum volume, with the emergence of filopodial-like protrusions from synaptic boutons of the Ib input. Decreased Is activity did not induce structural changes at its own synapses, but the coinnervating Ib motoneuron increased the number of synaptic boutons and AZs it formed. These findings indicate that tonic Ib and phasic Is motoneurons respond independently to changes in activity, with either functional or structural alterations in the Ib neuron occurring following ablation or reduced activity of the coinnervating Is input, respectively.SIGNIFICANCE STATEMENT Both invertebrate and vertebrate nervous systems display synaptic plasticity in response to behavioral experiences, indicating that underlying mechanisms emerged early in evolution. How specific neuronal classes innervating the same postsynaptic target display distinct types of plasticity is unclear. Here, we examined whether Drosophila tonic Ib and phasic Is motoneurons display competitive or cooperative interactions during innervation of the same muscle, or compensatory changes when the output of one motoneuron is altered. We established a system to differentially manipulate the motoneurons and examined the effects of cell type-specific changes to one of the inputs. Our findings indicate Ib and Is motoneurons respond differently to activity mismatch or loss of the coinnervating input, with the Ib subclass responding robustly compared with Is motoneurons.
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Affiliation(s)
- Nicole A Aponte-Santiago
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Kiel G Ormerod
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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Cunningham KL, Littleton JT. Synaptic Plasticity: Close Encounters of the Tonic and Phasic Kind. Curr Biol 2020; 29:R1196-R1198. [PMID: 31743679 DOI: 10.1016/j.cub.2019.09.033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Neuronal circuits have the capacity to maintain relatively constant activity in the face of perturbations that alter excitability or synaptic properties. A new study demonstrates that different classes of neurons co-innervating the same postsynaptic target express homeostatic plasticity with unique presynaptic features.
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Affiliation(s)
- Karen L Cunningham
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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23
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Lnenicka GA. Crayfish and Drosophila NMJs. Neurosci Lett 2020; 732:135110. [PMID: 32497734 DOI: 10.1016/j.neulet.2020.135110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 05/27/2020] [Accepted: 05/29/2020] [Indexed: 01/06/2023]
Abstract
Many synaptic studies have utilized the experimental advantages of the Arthropod NMJ and the most prominent preparations have been the crayfish and Drosophila larval NMJs. Early cellular studies in the crayfish established the framework for later molecular studies in Drosophila. The two neuromuscular systems are compared including the advantages presented by each preparation for cellular analysis. Beginning with the early work in the crayfish, research developments are followed in the areas of structure/function relationships, activity-dependent synaptic plasticity/development and synaptic homeostasis. A reoccurring theme in these studies is the regulation of active zone structure and function. Early studies in the crayfish focused on the role of active zone number/size and possible functional heterogeneity in regulating transmitter release. Recent studies in Drosophila have begun to characterize this heterogeneity using new approaches that combine imaging of transmitter release, Ca2+ influx and molecular composition for individual active zones.
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Affiliation(s)
- Gregory A Lnenicka
- Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, United States.
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