Caldendrin and myosin V regulate synaptic spine apparatus localization via ER stabilization in dendritic spines

AbstractExcitatory synapses of principal hippocampal neurons are frequently located on dendritic spines. The dynamic strengthening or weakening of individual inputs results in a great structural and molecular diversity of dendritic spines. Active spines with large Ca2+ transients are frequently invaded by a single protrusion from the endoplasmic reticulum (ER), which is dynamically transported into and out of spines by the actin-based motor myosin V. An increase in synaptic strength often correlates with stable anchoring of the ER, followed by the formation of the spine apparatus organelle. Here we show that synaptic ER stabilization depends on the interplay of two Ca2+-binding proteins: calmodulin serves as a light chain of myosin V and activates the motor function, whereas caldendrin acts as an inhibitor which transforms myosin into a stationary F-actin tether. Together, they provide a Ca2+-sensing module for fine-tuning myosin V activity and thereby regulate the formation of the spine apparatus in a subset of active dendritic spines.

Download Full-text

Characterization of neuronal synaptopodin reveals a myosin V-dependent mechanism of synaptopodin clustering at the post-synaptic sites

10.1101/526509 ◽

2019 ◽

Cited By ~ 3

Author(s):

Judit Gonzalez-Gallego ◽

Anja Konietzny ◽

Alberto Perez-Alvarez ◽

Julia Baer ◽

Urban Maier ◽

...

Keyword(s):

Dendritic Spines ◽

Pyramidal Neurons ◽

Super Resolution ◽

Myosin V ◽

Interaction Partners ◽

Spine Apparatus ◽

Tight Association ◽

Super Resolution Microscopy ◽

Dependent Mechanism

The spine apparatus (SA) is an endoplasmic reticulum-related organelle which is present in a subset of dendritic spines in cortical and pyramidal neurons. The synaptopodin protein localizes between the stacks of the spine apparatus and is essential for the formation of this unique organelle. Although several studies have demonstrated the significance of the SA and synaptopodin in calcium homeostasis and plasticity of dendritic spines, it is still unclear what factors contribute to its stability at the synapse and whether the SA is locally formed or it is actively delivered to the spines. In this study we show that synaptopodin clusters are stable at their locations. We found no evidence of active microtubule-based transport for synaptopodin. Instead new clusters were emerging in the spines, which we interpret as the SA being assembled on-site. Furthermore, using super-resolution microscopy we show a tight association of synaptopodin with actin filaments. We identify the actin-based motor proteins myosin V and VI as novel interaction partners of synaptopodin and demonstrate that myosin V is important for the formation and/or maintenance of the SA.

Download Full-text

Postsynaptic membrane and spine apparatus: Proximity in dendritic spines

Neuroscience Letters ◽

10.1016/0304-3940(79)90010-7 ◽

1979 ◽

Vol 11 (3) ◽

pp. 289-294 ◽

Cited By ~ 33

Author(s):

Sally B. Tarrant ◽

Aryeh Routtenberg

Keyword(s):

Dendritic Spines ◽

Postsynaptic Membrane ◽

Spine Apparatus

Download Full-text

Ultrastructural analysis of dendritic spine necks reveals a continuum of spine morphologies

10.1101/2021.02.18.431725 ◽

2021 ◽

Author(s):

Netanel Ofer ◽

Daniel R. Berger ◽

Narayanan Kasthuri ◽

Jeff W. Lichtman ◽

Rafael Yuste

Keyword(s):

Electron Microscopy ◽

Computer Vision ◽

Head And Neck ◽

Dendritic Spines ◽

Continuous Distribution ◽

Neck Length ◽

Neocortical Neurons ◽

Spine Apparatus ◽

Components Analysis ◽

Neck Diameter

AbstractDendritic spines are membranous protrusions, with a bulbous head connected to the dendrite by a thin neck, and receive essentially all excitatory inputs in most mammalian neurons. Spines have a wide variety of morphologies that likely have a significant effect on their biochemical and electrical properties. The question of whether spines belong to distinct morphological or functional subtypes or constitute a continuum is still open. To discern this, it is important to measure spine necks objectively. Recent advances in electron microscopy enable automatic reconstructions of 3D spines with nanometer precision. Analyzing ultrastructural reconstructions from mouse neocortical neurons with computer vision algorithms, we demonstrate that the vast majority of spines can be rigorously separated into head and neck components. Analysis of the head and neck morphologies reveals a continuous distribution of parameters. The spine neck diameter, but not the neck length, was correlated with the head volume. Spines with larger head volumes often had a spine apparatus and pairs of spines in a post-synaptic cell contacted by the same axon had similar head volumes. Our data are consistent with a lack of morphological categories of spines and indicate that the morphologies of the spine neck and head are independently regulated. These results have repercussions for our understanding of the function of dendritic spines in neuronal circuits.

Download Full-text

Dendritic spine geometry and spine apparatus organization govern the spatiotemporal dynamics of calcium

The Journal of General Physiology ◽

10.1085/jgp.201812261 ◽

2019 ◽

Vol 151 (8) ◽

pp. 1017-1034 ◽

Cited By ~ 15

Author(s):

Miriam Bell ◽

Tom Bartol ◽

Terrence Sejnowski ◽

Padmini Rangamani

Keyword(s):

Dendritic Spines ◽

Reaction Diffusion ◽

Three Dimensions ◽

Experimental Investigations ◽

Calcium Dynamics ◽

Surface Area Ratio ◽

Spine Head ◽

Reaction Diffusion Model ◽

Spine Apparatus ◽

Spine Function

Dendritic spines are small subcompartments that protrude from the dendrites of neurons and are important for signaling activity and synaptic communication. These subcompartments have been characterized to have different shapes. While it is known that these shapes are associated with spine function, the specific nature of these shape–function relationships is not well understood. In this work, we systematically investigated the relationship between the shape and size of both the spine head and spine apparatus, a specialized endoplasmic reticulum compartment within the spine head, in modulating rapid calcium dynamics using mathematical modeling. We developed a spatial multicompartment reaction–diffusion model of calcium dynamics in three dimensions with various flux sources, including N-methyl-D-aspartate receptors (NMDARs), voltage-sensitive calcium channels (VSCCs), and different ion pumps on the plasma membrane. Using this model, we make several important predictions. First, the volume to surface area ratio of the spine regulates calcium dynamics. Second, membrane fluxes impact calcium dynamics temporally and spatially in a nonlinear fashion. Finally, the spine apparatus can act as a physical buffer for calcium by acting as a sink and rescaling the calcium concentration. These predictions set the stage for future experimental investigations of calcium dynamics in dendritic spines.

Download Full-text

Effect of Associative Learning on Memory Spine Formation in Mouse Barrel Cortex

Neural Plasticity ◽

10.1155/2016/9828517 ◽

2016 ◽

Vol 2016 ◽

pp. 1-11 ◽

Cited By ~ 9

Author(s):

Malgorzata Jasinska ◽

Ewa Siucinska ◽

Ewa Jasek ◽

Jan A. Litwin ◽

Elzbieta Pyza ◽

...

Keyword(s):

Dendritic Spines ◽

Barrel Cortex ◽

Smooth Endoplasmic Reticulum ◽

Fear Learning ◽

Inhibitory Synapses ◽

Functional Representation ◽

Transmission Electron ◽

Spine Apparatus ◽

Permanent Memory ◽

Single Synapse

Associative fear learning, in which stimulation of whiskers is paired with mild electric shock to the tail, modifies the barrel cortex, the functional representation of sensory receptors involved in the conditioning, by inducing formation of new inhibitory synapses on single-synapse spines of the cognate barrel hollows and thus producing double-synapse spines. In the barrel cortex of conditioned, pseudoconditioned, and untreated mice, we analyzed the number and morphological features of dendritic spines at various maturation and stability levels: sER-free spines, spines containing smooth endoplasmic reticulum (sER), and spines containing spine apparatus. Using stereological analysis of serial sections examined by transmission electron microscopy, we found that the density of double-synapse spines containing spine apparatus was significantly increased in the conditioned mice. Learning also induced enhancement of the postsynaptic density area of inhibitory synapses as well as increase in the number of polyribosomes in such spines. In single-synapse spines, the effects of conditioning were less pronounced and included increase in the number of polyribosomes in sER-free spines. The results suggest that fear learning differentially affects single- and double-synapse spines in the barrel cortex: it promotes maturation and stabilization of double-synapse spines, which might possibly contribute to permanent memory formation, and upregulates protein synthesis in single-synapse spines.

Download Full-text

Morphological Variations in the Dendritic Spines of the Neocortex

Journal of Cell Science ◽

10.1242/jcs.5.2.509 ◽

1969 ◽

Vol 5 (2) ◽

pp. 509-529

Author(s):

E. G. JONES ◽

T. P. S. POWELL

Keyword(s):

Dendritic Spines ◽

Pyramidal Neurons ◽

Synaptic Contact ◽

Dendritic Tree ◽

Structural Variations ◽

Morphological Variations ◽

Spine Apparatus ◽

The Common ◽

Somatic Sensory Cortex ◽

Spherical Vesicles

The structural variations which occur in the dendritic spines of pyramidal neurons of the somatic sensory cortex of the cat are described, particular attention being paid to spines attached to different parts of the dendritic tree. Spines may be recognized particularly by the absence of neurotubules and the common presence of a spine apparatus, and they can be considered as pedunculated or sessile, depending upon the presence or absence of a narrow pedicle. Within these 2 categories spines may be rounded, cup-like or prismatic, can be large or small, and may show various degrees of inversion of the surface receiving a synaptic contact. While spines of every size and shape may be attached to dendrites of all diameters, there is a definite tendency for the largest spines to occur on the smallest dendrites and vice versa. Furthermore, the smallest dendrites possess the spines with the longest pedicles. Every dendritic spine receives 1 axon terminal containing spherical synaptic vesicles and ending in an asymmetrical synaptic contact. In addition, 10-20% of the spines receive a second terminal, which in some cases may contain spherical vesicles and terminate asymmetrically but in others contains small, flattened or pleomorphic vesicles and ends in a symmetrical contact. The additional terminal may end on the pedicle of the spine or on the parent dendrite near the attachment of the pedicle. In the latter site, asymmetrical synapses are commonly associated with an additional spine apparatus.

Download Full-text

Endoplasmic reticulum visits highly active spines and prevents runaway potentiation of synapses

Nature Communications ◽

10.1038/s41467-020-18889-5 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Alberto Perez-Alvarez ◽

Shuting Yin ◽

Christian Schulze ◽

John A. Hammer ◽

Wolfgang Wagner ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Dendritic Spines ◽

Low Frequency ◽

Pyramidal Cells ◽

Long Term Potentiation ◽

Dominant Negative ◽

Synaptic Activity ◽

Small Subset ◽

Myosin V

Abstract In hippocampal pyramidal cells, a small subset of dendritic spines contain endoplasmic reticulum (ER). In large spines, ER frequently forms a spine apparatus, while smaller spines contain just a single tubule of smooth ER. Here we show that the ER visits dendritic spines in a non-random manner, targeting spines during periods of high synaptic activity. When we blocked ER motility using a dominant negative approach against myosin V, spine synapses became stronger compared to controls. We were not able to further potentiate these maxed-out synapses, but long-term depression (LTD) was readily induced by low-frequency stimulation. We conclude that the brief ER visits to active spines have the important function of preventing runaway potentiation of individual spine synapses, keeping most of them at an intermediate strength level from which both long-term potentiation (LTP) and LTD are possible.

Download Full-text

Endoplasmic reticulum visits highly active spines and prevents runaway potentiation of synapses

10.1101/2020.07.30.228155 ◽

2020 ◽

Cited By ~ 1

Author(s):

Alberto Perez-Alvarez ◽

Shuting Yin ◽

Christian Schulze ◽

John A. Hammer ◽

Wolfgang Wagner ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Dendritic Spines ◽

Low Frequency ◽

Pyramidal Cells ◽

Dominant Negative ◽

Synaptic Activity ◽

Small Subset ◽

Myosin V ◽

Highly Active ◽

Frequency Stimulation

AbstractIn hippocampal pyramidal cells, a small subset of dendritic spines contain endoplasmic reticulum (ER). In large spines, ER frequently forms a spine apparatus, while smaller spines contain just a single tubule of smooth ER. Here we show that the ER visits dendritic spines in a non-random manner, targeting spines during periods of high synaptic activity. When we blocked ER motility using a dominant negative approach against myosin V, spine synapses became stronger compared to controls. We were not able to further potentiate these maxed-out synapses, but LTD was readily induced by low-frequency stimulation. We conclude that the brief ER visits to active spines have the important function of preventing runaway potentiation of individual spine synapses, keeping most of them at an intermediate strength level from which both LTP and LTD are possible.

Download Full-text

Properties and proximity proteomics of synaptopodin provide insight into the molecular organization of the spine apparatus of dendritic spines

10.1101/2021.12.30.474557 ◽

2021 ◽

Author(s):

Hanieh Falahati ◽

Yumei Wu ◽

Vanessa Feuerer ◽

Pietro De Camilli

Keyword(s):

Dendritic Spines ◽

Binding Protein ◽

Molecular Organization ◽

Actin Binding ◽

Small Subset ◽

Dense Matrix ◽

Actin Binding Protein ◽

Spine Apparatus ◽

Underlying Mechanisms

The spine apparatus is a specialization of the neuronal ER in dendritic spines consisting of stacks of interconnected cisterns separated by a dense matrix. Synaptopodin, a specific actin binding protein of the spine apparatus, is essential for its formation, but the underlying mechanisms remain unknown. We show that synaptopodin, when expressed in fibroblasts, forms actin-rich structures with connections to the ER, and that an ER-tethered synaptopodin assembles into liquid condensates. We also identified protein neighbors of synaptopodin in spines by in vivo proximity biotinylation. We validated a small subset of such proteins and showed that they co-assemble with synaptopodin in living cells. One of them is Pdlim7, an actin binding protein not previously identified in spines, and we show its precise colocalization with synaptopodin. We suggest that the matrix of the spine apparatus has the property of a liquid protein condensate generated by a multiplicity of low affinity interactions.

Download Full-text