Vesicle Fusion & Synaptic Transmission
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Questions and Answers

Which of the following is the primary role of SNAP-25 in vesicle fusion?

  • Zippering v- and t-SNAREs together to bring the vesicle and membrane into close proximity. (correct)
  • Serving as the vesicular SNARE protein.
  • Initiating the v-SNARE and t-SNARE interaction.
  • Acting as the calcium sensor to trigger fusion.

FRET (Förster Resonance Energy Transfer) is effective for measuring distances greater than 10nm between molecules.

False (B)

What is the function of the active zone (AZ) in neuronal signaling?

The active zone serves as a platform for rapid synaptic vesicle fusion following calcium influx.

In the SNARE complex, syntaxin is referred to as a ______ protein.

<p>target SNARE</p> Signup and view all the answers

Match the following SNARE proteins with their roles in vesicle fusion:

<p>Synaptobrevin = v-SNARE (vesicular SNARE protein) Syntaxin = t-SNARE (target SNARE protein) SNAP-25 = Zipper between v- and t-SNARE</p> Signup and view all the answers

What is the significance of using liposomes in FRET experiments designed to study vesicle fusion?

<p>Liposomes mimic the cellular membrane environment, allowing for the reconstitution of vesicle fusion in vitro. (D)</p> Signup and view all the answers

Active zone formation requires the presence of a postsynaptic partner.

<p>False (B)</p> Signup and view all the answers

What is the effect of calcium influx on the speed of vesicle fusion, and why is it important?

<p>Calcium influx greatly accelerates vesicle fusion. This rapid fusion is crucial for fast neurotransmitter release and efficient synaptic transmission.</p> Signup and view all the answers

What does the fluorescence signal in FM destaining indicate about the dye molecule's environment?

<p>It has interacted with a charged (polar) solvent like water. (C)</p> Signup and view all the answers

Active-zone assembly requires a postsynaptic partner.

<p>False (B)</p> Signup and view all the answers

What is the role of the small GTPase Rab3 in synapse development?

<p>normal AZ distribution and pre/post matching</p> Signup and view all the answers

Partial axonal co-transport of active zone proteins and synaptic vesicles in presynaptic lysosome-related vesicles (PLVs) requires ______.

<p>Arl8</p> Signup and view all the answers

Match the following:

<p>Synapse Defective-1 = Synaptic vesicle targeting in Drosophila and mouse CNS Prl-1 Phosphatase = Specifies subcellular synapse location and axon branching Neurexin = Clusters glutamate- and GABA postsynaptic scaffolding proteins in dendrites Neuroligin = Clusters glutamate- and GABA-containing synaptic vesicles</p> Signup and view all the answers

What role do Neuroligin isoforms play at synapses?

<p>Determining the sign (excitatory or inhibitory) of a synapse. (C)</p> Signup and view all the answers

Microtubule (MT) polarity and specific MT-associated proteins are involved in targeting synaptic components to synapses in axons or dendrites.

<p>True (A)</p> Signup and view all the answers

What is the primary function of synaptic cell adhesion molecules (CAMs)?

<p>Inducing pre- or postsynaptic formation. (D)</p> Signup and view all the answers

What is the primary role of non-synaptic clusters of postsynaptic scaffolding proteins in synapse formation?

<p>Serving as a foundation for presynaptic terminals to become active. (D)</p> Signup and view all the answers

Contact between pre- and postsynaptic neurons is sufficient to initiate and complete synapse formation without the need for scaffolding proteins.

<p>False (B)</p> Signup and view all the answers

What technique can be used to induce neurotransmitter release at individual synapses to study spinogenesis?

<p>2-Photon glutamate uncaging</p> Signup and view all the answers

The rapid induction of spinogenesis can be achieved through presynaptic activity, a process where ________ is essential.

<p>Neuroligin-1</p> Signup and view all the answers

What is the role of Munc13 in spinogenesis, specifically when induced by glutamate uncaging?

<p>Spine development induced by glutamate uncaging can occur normally even without Munc13 function. (D)</p> Signup and view all the answers

Inhibitory and excitatory synapses are characterized by the same pre- and postsynaptic proteins.

<p>False (B)</p> Signup and view all the answers

Match the following molecules/processes with their roles in synapse formation:

<p>PSD-95 = Recruited to synapses from cytoplasmic pools to build postsynaptic density Glutamate Uncaging = Induces neurotransmitter release to study spinogenesis Munc13 = Presynaptic protein cluster representing release sites Scaffolding proteins = Essential for synapse formation, not contact alone</p> Signup and view all the answers

What is the direct outcome of glutamate uncaging in mature synapses?

<p>Induction of spine growth and PSD-95 accumulation. (B)</p> Signup and view all the answers

Which of the following best describes the role of transsynaptic cell adhesion molecules?

<p>Play a significant role in both synapse formation and synaptic plasticity at mature synapses. (D)</p> Signup and view all the answers

The interaction between cell adhesion molecules dictates synaptic specificity, implying a 'CAM code'.

<p>True (A)</p> Signup and view all the answers

What is the function of Cbln1 in the context of synapse formation?

<p>Cbln1 mediates the interaction between postsynaptic GluRδ2 and presynaptic neurexins.</p> Signup and view all the answers

Using PALM, aligned 'nanoclusters' of presynaptic and postsynaptic molecules are revealed, forming what are known as ______.

<p>nanocolumns</p> Signup and view all the answers

What is the primary function of Photoactivated Localization Microscopy (PALM) in studying synapses?

<p>Estimating the number of PSD-95 molecules and increasing spatial resolution. (C)</p> Signup and view all the answers

Postsynaptic assembly always precedes presynaptic assembly during synaptogenesis.

<p>False (B)</p> Signup and view all the answers

Match the molecule/technique with its function in synapse formation and analysis:

<p>Cbln1 = Mediates interaction between GluRδ2 and neurexins PALM = Super-resolution microscopy for estimating molecule number Nanocolumns = Aligned pre- and postsynaptic molecule clusters Cell adhesion molecules = Determine synaptic specificity</p> Signup and view all the answers

What determines synaptic transmission strength?

<p>The degree of postsynaptic voltage or current change in response to action potential stimulation. (A)</p> Signup and view all the answers

What is the primary outcome of synapse elimination during maturation?

<p>Monosynaptic innervation, where each target is innervated by only one synapse. (A)</p> Signup and view all the answers

Long-term potentiation (LTP) can be induced equally at any climbing fiber input, regardless of its initial size.

<p>False (B)</p> Signup and view all the answers

What type of signaling is involved in the elimination of weaker synapses by the 'winner synapse' after LTP induction?

<p>postsynaptic Ca2+/Arc signaling</p> Signup and view all the answers

During the development of climbing fiber-cerebellar Purkinje synapses, all synapses but ______ are eliminated.

<p>one</p> Signup and view all the answers

Which of the following is required for activity-dependent synapse elimination of cerebellar climbing fiber-Purkinje cell synapses?

<p>PQ-type Ca2+ channels and Arc (C)</p> Signup and view all the answers

Input segregation at the neuromuscular junction (NMJ) occurs after terminal withdrawal of synaptic inputs.

<p>False (B)</p> Signup and view all the answers

Match the process with its description:

<p>Maturation = Synapse elimination leading to monosynaptic innervation Competition = Elimination of all but one synapse during development LTP = Strengthening of the 'winner synapse'</p> Signup and view all the answers

Synchronous activation of climbing fiber (CF) and Purkinje cell (PC) is commonly used to induce:

<p>Long-term potentiation (LTP) (A)</p> Signup and view all the answers

Flashcards

Synaptic Modules

Specialized structures where neurotransmitter release occurs.

Active Zone

The area on the presynaptic neuron where vesicles fuse to release neurotransmitters.

SNAREs

A protein complex responsible for vesicle fusion.

Synaptobrevin

v-SNARE, found on vesicles; interacts with t-SNAREs on the target membrane.

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Syntaxin

t-SNARE, found on the target membrane; interacts with v-SNAREs.

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SNAP-25

SNARE protein that 'zips' v- and t-SNAREs together, bringing membranes into close proximity for fusion.

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FRET

A technique to measure distances between molecules using energy transfer.

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Postsynaptic Density (PSD)

Protein scaffold at the postsynaptic membrane, important for receptor localization and signaling.

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Self-assembly of active zones

Active zones can assemble independently of postsynaptic partners.

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FM Dye Destaining

Fluorescence occurs when FM dyes encounter charged (polar) membranes.

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PLV Co-transport

Some active zone proteins and synaptic vesicles travel together via PLVs, requiring Arl8.

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Synapse Defective-1

Required for normal synaptic vesicle targeting in the PNS, CNS, and mouse CNS

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Small GTPase Rab3

Required for normal active zone distribution and pre/post matching.

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Prl-1 Phosphatase

Prl-1 specifies synapse location and axon branching in the Drosophila CNS

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Neurexin in Non-Neuronal Cells

Expression induces accumulation of postsynaptic scaffolding proteins in dendrites

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Neuroligin Isoforms

Determine whether a synapse is excitatory or inhibitory

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Nonsynaptic Scaffold Clusters

Initial clusters of postsynaptic proteins before synapse formation. May involve co-transport of proteins.

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Sites Apposed to Nonsynaptic Clusters

These are often transformed into active presynaptic terminals.

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Glutamate Uncaging

A technique using light to trigger neurotransmitter release at a specific synapse. Used to induce spine growth.

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Spinogenesis

Spine formation, rapidly induced by presynaptic activity.

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Neuroligin-1 Role

Required for glutamate uncaging-induced spinogenesis.

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PSD-95 Accumulation

Accumulation of PSD-95 at mature synapses induced by glutamate uncaging, indicating synaptic strengthening.

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Spinogenesis without Release

Spine development can still occur without neurotransmitter release.

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Synapse-Specific Proteins

Excitatory and inhibitory synapses have distinct sets of proteins that define their function.

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Transsynaptic Molecules

Molecules that interact across the synaptic cleft, connecting pre- and postsynaptic neurons.

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CAM Interaction

Interaction between identical (homophilic) or different (heterophilic) cell adhesion molecules at the synapse.

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GluRδ2 Role

A postsynaptic protein that interacts with presynaptic neurexins, mediated by Cbln1.

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CAM Code

Specific roles played by cell adhesion molecules in forming connections; a 'code' that determines where synapses form.

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PALM Microscopy

A super-resolution microscopy technique using stochastic activation of fluorophores to increase spatial resolution.

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Nanocolumns

Using PALM, scientists discovered aligned clusters of pre- and postsynaptic molecules.

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Synaptogenesis Timing

Cell adhesion molecule interaction, then presynaptic assembly, then postsynaptic assembly.

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Synaptic Strength

The degree of postsynaptic voltage/current change caused by an action potential.

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Synapse Strength & Number

Synaptic strength depends on the number of synapses on a dendritic branch.

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Synapse Elimination

The process where multiple synapses on a neuron are reduced to a single synapse during development.

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Climbing Fiber Synapse

During development, all but one synapse are eliminated on Purkinje cells, ensuring single, strong input.

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Input Segregation Order

Input segregation at the NMJ precedes the withdrawal of axon terminals.

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Dominant Climbing Fiber

The 'largest' climbing fiber input onto a Purkinje cell becomes stronger over time.

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Long-Term Potentiation (LTP)

Strengthening of synapses that are synchronously activated, increasing the conductance of AMPA receptors.

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Winner Synapse

The strongest synapse undergoes LTP and suppresses weaker synapses through postsynaptic signaling.

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Synapse elimination requirements

Activity-dependent synapse elimination requires PQ-type Ca2+ channels and Arc protein

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Study Notes

Synaptic Modules

  • Synaptic transmission involves presynaptic and postsynaptic elements.
    • Presynaptic: Vesicle fusion and active zone
    • Postsynaptic: Postsynaptic density (PSD)

Presynaptic Assembly

Vesicle Fusion

  • SNAREs mediate vesicle fusion:
    • Synaptobrevin is a vesicular SNARE (v-SNARE).
    • Syntaxin is a target SNARE (t-SNARE).
    • SNAP-25 zippers v-SNARE and t-SNARE together.
    • The zipped complex facilitates vesicle-membrane fusion.
  • FRET (Förster/Fluorescence Resonance Energy Transfer) probes SNARE complex distances.
    • Energy transfer depends on fluorophore distance; effective under 6-8 nm.
    • Donor excitation transfers energy to the acceptor, dimming the donor.
  • Synaptic vesicle fusion energy decreases if vesicles fuse with liposomes.
  • Vesicle fusion can be reconstituted in vitro without active zone components or Ca2+.
  • SNARE-complex mediated fusion is slow (ca. 40').
    • Fast fusion requires Ca-influx.

Active Zone Assembly

  • The active zone (AZ) facilitates rapid synaptic vesicle fusion upon Ca2+ influx.
    • The AZ membrane is decorated by cytomatrix proteins.
  • Presynaptic differentiation is induced by postsynaptic cell adhesion molecules like Neuroligin.
  • Active zone formation occurs after contact with polylysine-coated beads.
  • Active zone assembly doesn't require a postsynaptic partner (self-assembly).
  • Orphan synapses can undergo exocytosis.
  • Partial axonal co-transport of active zone proteins and synaptic vesicles requires Arl8.
  • Microtubule polarity and MT-associated proteins target synaptic components to synapses.
  • Synapse Defective-1 is essential for synaptic vesicle targeting in Drosophila and mouse CNS.
  • Rab3 GTPase is needed for AZ distribution; no transmission defect in rab3 mutants.

Post-Synaptic Density (PSD)

  • Neurexin expression in non-neuronal cells clusters glutamate- and GABA-postsynaptic scaffolding proteins in dendrites.
  • Neuroligin expression in non-neuronal cells clusters glutamate- and GABA-containing synaptic vesicles
  • Neuroligin isoforms determine synapse types.

Synaptic CAMs

  • Synaptic CAMs (cell adhesion molecules) induce pre- or postsynaptic formation.
  • Neuroligins, LRRTMS, SALMS, SliTrks induce presynaptic features.
  • Neurexins, Neur. pentraxin receptor, Teneurins, and PTPRS induce postsynaptic features.

PSD Assembly

  • Nonsynaptic clusters of postsynaptic scaffolding proteins co-transport postsynaptic proteins.
  • Contact, by itself, isn't enough to drive synapse formation; scaffolding proteins are needed.
  • Sites near nonsynaptic scaffold clusters can transform into presynaptic terminals
  • AMPARs and NMDARs are transported in different vesicles; PSD-95 and SAP-90 use cytoplasmic pools for synapse recruitment.

Glutamate Uncaging

  • Two-photon glutamate uncaging induces neurotransmitter release at individual synapses.
  • Spinogenesis is rapidly induced, driven by presynaptic activity.
  • Neuroligin-1 is essential for glutamate uncaging induced spinogenesis.
  • Munc13 clusters are likely presynaptic release sites.
  • Glutamate uncaging leads to spine growth and accumulation of the postsynaptic density protein PSD-95
  • Normal spine and uncaging-induced development occurs in Munc13-KO mice without neurotransmitter release.
  • Glutamate uncaging induces AMPAR recruitment in Munc13-KO mice.

Postsynaptic and Transsynaptic Molecules

  • Specific pre- and postsynaptic proteins characterize excitatory and inhibitory synapses.
  • GluRd2 interacts with presynaptic neurexins in the presence of "cerebellin 1 precursor protein" (Cbln1)
  • Cell adhesion molecules play specific roles in synapse formation "CAM code" is involved in determining synaptic specificity.
  • Transsynaptic cell adhesion molecules are involved in synapse formation and plasticity.
  • Cell adhesion molecules have links to autism.

Timing of Synaptogenesis

  • Cell adhesion molecule interaction leads to presynaptic assembly, and then postsynaptic assembly

Maturation and Competition

  • Synapse transmission strength depends on postsynaptic voltage/current change during action potential stimulation
  • Neurotransmitter release probability relies on the number of synapses on a dendritic branch.
  • Many synapses face elimination during maturation, leading to monosynaptic innervation.
  • Input segregation precedes terminal withdrawal from the NMJ.
  • Most synapses are eliminated during development of climbing fiber-cerebellar Purkinje synapses.

Plasticity and Competition

  • Synchronous activation of climbing fiber (CF) and Purkinje cell (PC) induces long-term potentiation (LTP).
  • LTP is induced at large inputs with increased AMPA-type glutamate receptor conductance.
  • The "winner synapse" undergoes LTP and eliminates other synapses through postsynaptic Ca2+/Arc signaling.
  • Transsynaptic signaling via cell adhesion molecules is key in synaptic development.
  • Maturation involves synapse elimination and is activity-dependent.

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Description

Examine SNARE proteins (SNAP-25, syntaxin), FRET's role in measuring distances in vesicle fusion, and active zones. Explore calcium influx effects, FM destaining, and Rab3's role in synapse development. Study axonal co-transport in neurons.

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