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Regulation of synaptic vesicle docking by different classes of macromolecules in active zone material.

Szule JA, Harlow ML, Jung JH, De-Miguel FF, Marshall RM, McMahan UJ - PLoS ONE (2012)

Bottom Line: The docking of synaptic vesicles at active zones on the presynaptic plasma membrane of axon terminals is essential for their fusion with the membrane and exocytosis of their neurotransmitter to mediate synaptic impulse transmission.We conclude that vesicle movement toward and maintenance at docking sites on the presynaptic membrane are directed by an orderly succession of stable interactions between the vesicles and distinct classes of AZM macromolecules positioned at different distances from the membrane.Establishing the number, arrangement and sequence of association of AZM macromolecules involved in vesicle docking provides an anatomical basis for testing and extending concepts of docking mechanisms provided by biochemistry.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Stanford University School of Medicine, Stanford, California, United States of America.

ABSTRACT
The docking of synaptic vesicles at active zones on the presynaptic plasma membrane of axon terminals is essential for their fusion with the membrane and exocytosis of their neurotransmitter to mediate synaptic impulse transmission. Dense networks of macromolecules, called active zone material, (AZM) are attached to the presynaptic membrane next to docked vesicles. Electron tomography has shown that some AZM macromolecules are connected to docked vesicles, leading to the suggestion that AZM is somehow involved in the docking process. We used electron tomography on the simply arranged active zones at frog neuromuscular junctions to characterize the connections of AZM to docked synaptic vesicles and to search for the establishment of such connections during vesicle docking. We show that each docked vesicle is connected to 10-15 AZM macromolecules, which fall into four classes based on several criteria including their position relative to the presynaptic membrane. In activated axon terminals fixed during replacement of docked vesicles by previously undocked vesicles, undocked vesicles near vacated docking sites on the presynaptic membrane have connections to the same classes of AZM macromolecules that are connected to docked vesicles in resting terminals. The number of classes and the total number of macromolecules to which the undocked vesicles are connected are inversely proportional to the vesicles' distance from the presynaptic membrane. We conclude that vesicle movement toward and maintenance at docking sites on the presynaptic membrane are directed by an orderly succession of stable interactions between the vesicles and distinct classes of AZM macromolecules positioned at different distances from the membrane. Establishing the number, arrangement and sequence of association of AZM macromolecules involved in vesicle docking provides an anatomical basis for testing and extending concepts of docking mechanisms provided by biochemistry.

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Angle of approach of main body AZM macromolecules to docked vesicles.The docked vesicles shown at the arrows in Figure 4 together with selected members of their associated AZM macromolecules were projected and traced onto a two dimensional plane. Lines drawn parallel to the ribs (yellow gold; A), spars (red; B) and booms (purple; C) approach a vesicle at different angles relative to perpendicular lines drawn to the plane of the beam (brown gold). Measurements of such angles from many docked vesicles reveal that the average angle of approach is significantly different for each class of AZM macromolecule, as detailed in the text and as shown here for single macromolecules from each class: A, 5°; B, 17°; and C, 27°.
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pone-0033333-g005: Angle of approach of main body AZM macromolecules to docked vesicles.The docked vesicles shown at the arrows in Figure 4 together with selected members of their associated AZM macromolecules were projected and traced onto a two dimensional plane. Lines drawn parallel to the ribs (yellow gold; A), spars (red; B) and booms (purple; C) approach a vesicle at different angles relative to perpendicular lines drawn to the plane of the beam (brown gold). Measurements of such angles from many docked vesicles reveal that the average angle of approach is significantly different for each class of AZM macromolecule, as detailed in the text and as shown here for single macromolecules from each class: A, 5°; B, 17°; and C, 27°.

Mentions: Surface models were generated from 1.0 nm thick serial virtual slices through a reconstructed active zone sectioned near its horizontal plane. The slice series was in the same plane. A) The ribs (yellow gold) and beams (brown gold) of the superficial layer of the AZM extend throughout the length of the active zone except at the gap, where the superficial layer was not included in the tissue section. Multiple ribs connect to each docked vesicle except at the upper right, where the vesicle(s) was too close to the edge of the section to be clearly discerned in the reconstruction. Ribs in some regions are not distinguishable from their neighbors because of the model’s angle of rotation. B) The intermediate layer shown together with the superficial layer. Steps (gray) are centered between opposing pairs of docked vesicles (as in solid box) along straight stretches of the active zone. The positioning of the steps is less regular where there is an angular change in the active zone’s long axis (dashed boxes). Typically, each docked vesicle is connected to spars (red) arising from two steps. C) The deep layer is shown together with the superficial and intermediate layers. Masts (dark green) overlay steps (compare with B). Multiple booms (purple) extend from each mast to connect to docked vesicles. D,E,F) Near transverse views of the surface models shown in A,B, and C from the regions in those panels marked d, e and f respectively. Arrows in A indicate the vesicles and associated AZM macromolecules used in Figure 5 to demonstrate our method for measuring the angle of approach of different classes of AZM macromolecules to docked vesicles. Topmasts were not included in the tissue section.


Regulation of synaptic vesicle docking by different classes of macromolecules in active zone material.

Szule JA, Harlow ML, Jung JH, De-Miguel FF, Marshall RM, McMahan UJ - PLoS ONE (2012)

Angle of approach of main body AZM macromolecules to docked vesicles.The docked vesicles shown at the arrows in Figure 4 together with selected members of their associated AZM macromolecules were projected and traced onto a two dimensional plane. Lines drawn parallel to the ribs (yellow gold; A), spars (red; B) and booms (purple; C) approach a vesicle at different angles relative to perpendicular lines drawn to the plane of the beam (brown gold). Measurements of such angles from many docked vesicles reveal that the average angle of approach is significantly different for each class of AZM macromolecule, as detailed in the text and as shown here for single macromolecules from each class: A, 5°; B, 17°; and C, 27°.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3306385&req=5

pone-0033333-g005: Angle of approach of main body AZM macromolecules to docked vesicles.The docked vesicles shown at the arrows in Figure 4 together with selected members of their associated AZM macromolecules were projected and traced onto a two dimensional plane. Lines drawn parallel to the ribs (yellow gold; A), spars (red; B) and booms (purple; C) approach a vesicle at different angles relative to perpendicular lines drawn to the plane of the beam (brown gold). Measurements of such angles from many docked vesicles reveal that the average angle of approach is significantly different for each class of AZM macromolecule, as detailed in the text and as shown here for single macromolecules from each class: A, 5°; B, 17°; and C, 27°.
Mentions: Surface models were generated from 1.0 nm thick serial virtual slices through a reconstructed active zone sectioned near its horizontal plane. The slice series was in the same plane. A) The ribs (yellow gold) and beams (brown gold) of the superficial layer of the AZM extend throughout the length of the active zone except at the gap, where the superficial layer was not included in the tissue section. Multiple ribs connect to each docked vesicle except at the upper right, where the vesicle(s) was too close to the edge of the section to be clearly discerned in the reconstruction. Ribs in some regions are not distinguishable from their neighbors because of the model’s angle of rotation. B) The intermediate layer shown together with the superficial layer. Steps (gray) are centered between opposing pairs of docked vesicles (as in solid box) along straight stretches of the active zone. The positioning of the steps is less regular where there is an angular change in the active zone’s long axis (dashed boxes). Typically, each docked vesicle is connected to spars (red) arising from two steps. C) The deep layer is shown together with the superficial and intermediate layers. Masts (dark green) overlay steps (compare with B). Multiple booms (purple) extend from each mast to connect to docked vesicles. D,E,F) Near transverse views of the surface models shown in A,B, and C from the regions in those panels marked d, e and f respectively. Arrows in A indicate the vesicles and associated AZM macromolecules used in Figure 5 to demonstrate our method for measuring the angle of approach of different classes of AZM macromolecules to docked vesicles. Topmasts were not included in the tissue section.

Bottom Line: The docking of synaptic vesicles at active zones on the presynaptic plasma membrane of axon terminals is essential for their fusion with the membrane and exocytosis of their neurotransmitter to mediate synaptic impulse transmission.We conclude that vesicle movement toward and maintenance at docking sites on the presynaptic membrane are directed by an orderly succession of stable interactions between the vesicles and distinct classes of AZM macromolecules positioned at different distances from the membrane.Establishing the number, arrangement and sequence of association of AZM macromolecules involved in vesicle docking provides an anatomical basis for testing and extending concepts of docking mechanisms provided by biochemistry.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Stanford University School of Medicine, Stanford, California, United States of America.

ABSTRACT
The docking of synaptic vesicles at active zones on the presynaptic plasma membrane of axon terminals is essential for their fusion with the membrane and exocytosis of their neurotransmitter to mediate synaptic impulse transmission. Dense networks of macromolecules, called active zone material, (AZM) are attached to the presynaptic membrane next to docked vesicles. Electron tomography has shown that some AZM macromolecules are connected to docked vesicles, leading to the suggestion that AZM is somehow involved in the docking process. We used electron tomography on the simply arranged active zones at frog neuromuscular junctions to characterize the connections of AZM to docked synaptic vesicles and to search for the establishment of such connections during vesicle docking. We show that each docked vesicle is connected to 10-15 AZM macromolecules, which fall into four classes based on several criteria including their position relative to the presynaptic membrane. In activated axon terminals fixed during replacement of docked vesicles by previously undocked vesicles, undocked vesicles near vacated docking sites on the presynaptic membrane have connections to the same classes of AZM macromolecules that are connected to docked vesicles in resting terminals. The number of classes and the total number of macromolecules to which the undocked vesicles are connected are inversely proportional to the vesicles' distance from the presynaptic membrane. We conclude that vesicle movement toward and maintenance at docking sites on the presynaptic membrane are directed by an orderly succession of stable interactions between the vesicles and distinct classes of AZM macromolecules positioned at different distances from the membrane. Establishing the number, arrangement and sequence of association of AZM macromolecules involved in vesicle docking provides an anatomical basis for testing and extending concepts of docking mechanisms provided by biochemistry.

Show MeSH
Related in: MedlinePlus