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Regulated Dynamic Trafficking of Neurexins Inside and Outside of Synaptic Terminals.
J Neurosci 2015; 35(40):13629-47JN

Abstract

Synapses depend on trafficking of key membrane proteins by lateral diffusion from surface populations and by exocytosis from intracellular pools. The cell adhesion molecule neurexin (Nrxn) plays essential roles in synapses, but the dynamics and regulation of its trafficking are unknown. Here, we performed single-particle tracking and live imaging of transfected, epitope-tagged Nrxn variants in cultured rat and mouse wild-type or knock-out neurons. We observed that structurally larger αNrxn molecules are more mobile in the plasma membrane than smaller βNrxns because αNrxns displayed higher diffusion coefficients in extrasynaptic regions and excitatory or inhibitory terminals. We found that well characterized interactions with extracellular binding partners regulate the surface mobility of Nrxns. Binding to neurexophilin-1 (Nxph1) reduced the surface diffusion of αNrxns when both molecules were coexpressed. Conversely, impeding other interactions by insertion of splice sequence #4 or removal of extracellular Ca(2+) augmented the mobility of αNrxns and βNrxns. We also determined that fast axonal transport delivers Nrxns to the neuronal surface because Nrxns comigrate as cargo on synaptic vesicle protein transport vesicles (STVs). Unlike surface mobility, intracellular transport of βNrxn(+) STVs was faster than that of αNrxns, but both depended on the microtubule motor protein KIF1A and neuronal activity regulated the velocity. Large spontaneous fusion of Nrxn(+) STVs occurred simultaneously with synaptophysin on axonal membranes mostly outside of active presynaptic terminals. Surface Nrxns enriched at synaptic terminals where αNrxns and Nxph1/αNrxns recruited GABAAR subunits. Therefore, our results identify regulated dynamic trafficking as an important property of Nrxns that corroborates their function at synapses.

SIGNIFICANCE STATEMENT

Synapses mediate most functions in our brains and depend on the precise and timely delivery of key molecules throughout life. Neurexins (Nrxns) are essential synaptic cell adhesion molecules that are involved in synaptic transmission and differentiation of synaptic contacts. In addition, Nrxns have been linked to neuropsychiatric diseases such as autism. Because little is known about the dynamic aspects of trafficking of neurexins to synapses, we investigated this important question using single-molecule tracking and time-lapse imaging. We identify distinct differences between major Nrxn variants both in surface mobility and during intracellular transport. Because their dynamic behavior is highly regulated, for example, by different binding activities, these processes have immediate consequences for the function of Nrxns at synapses.

Authors+Show Affiliations

Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany.Molecular Physiology Group, Leibniz-Institute of Neurobiology, 39118 Magdeburg, Germany.Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany, Molecular Physiology Group, Leibniz-Institute of Neurobiology, 39118 Magdeburg, Germany.Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany.Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany.Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany, Molecular Physiology Group, Leibniz-Institute of Neurobiology, 39118 Magdeburg, Germany.Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany.Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany, Cluster of Excellence EXC 1003, Cells in Motion, 48149 Münster, Germany, and Markus.Missler@uni-muenster.de Martin.Heine@ifn-magdeburg.de.Molecular Physiology Group, Leibniz-Institute of Neurobiology, 39118 Magdeburg, Germany, Center for Behavioral Brain Sciences, 39118 Magdeburg, Germany Markus.Missler@uni-muenster.de Martin.Heine@ifn-magdeburg.de.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

26446217

Citation

Neupert, Christian, et al. "Regulated Dynamic Trafficking of Neurexins Inside and Outside of Synaptic Terminals." The Journal of Neuroscience : the Official Journal of the Society for Neuroscience, vol. 35, no. 40, 2015, pp. 13629-47.
Neupert C, Schneider R, Klatt O, et al. Regulated Dynamic Trafficking of Neurexins Inside and Outside of Synaptic Terminals. J Neurosci. 2015;35(40):13629-47.
Neupert, C., Schneider, R., Klatt, O., Reissner, C., Repetto, D., Biermann, B., ... Heine, M. (2015). Regulated Dynamic Trafficking of Neurexins Inside and Outside of Synaptic Terminals. The Journal of Neuroscience : the Official Journal of the Society for Neuroscience, 35(40), pp. 13629-47. doi:10.1523/JNEUROSCI.4041-14.2015.
Neupert C, et al. Regulated Dynamic Trafficking of Neurexins Inside and Outside of Synaptic Terminals. J Neurosci. 2015 Oct 7;35(40):13629-47. PubMed PMID: 26446217.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Regulated Dynamic Trafficking of Neurexins Inside and Outside of Synaptic Terminals. AU - Neupert,Christian, AU - Schneider,Romy, AU - Klatt,Oliver, AU - Reissner,Carsten, AU - Repetto,Daniele, AU - Biermann,Barbara, AU - Niesmann,Katharina, AU - Missler,Markus, AU - Heine,Martin, PY - 2015/10/9/entrez PY - 2015/10/9/pubmed PY - 2016/1/14/medline KW - GABA(A) receptors KW - autism KW - imaging KW - neuroligin KW - quantum dots KW - synapse function SP - 13629 EP - 47 JF - The Journal of neuroscience : the official journal of the Society for Neuroscience JO - J. Neurosci. VL - 35 IS - 40 N2 - UNLABELLED: Synapses depend on trafficking of key membrane proteins by lateral diffusion from surface populations and by exocytosis from intracellular pools. The cell adhesion molecule neurexin (Nrxn) plays essential roles in synapses, but the dynamics and regulation of its trafficking are unknown. Here, we performed single-particle tracking and live imaging of transfected, epitope-tagged Nrxn variants in cultured rat and mouse wild-type or knock-out neurons. We observed that structurally larger αNrxn molecules are more mobile in the plasma membrane than smaller βNrxns because αNrxns displayed higher diffusion coefficients in extrasynaptic regions and excitatory or inhibitory terminals. We found that well characterized interactions with extracellular binding partners regulate the surface mobility of Nrxns. Binding to neurexophilin-1 (Nxph1) reduced the surface diffusion of αNrxns when both molecules were coexpressed. Conversely, impeding other interactions by insertion of splice sequence #4 or removal of extracellular Ca(2+) augmented the mobility of αNrxns and βNrxns. We also determined that fast axonal transport delivers Nrxns to the neuronal surface because Nrxns comigrate as cargo on synaptic vesicle protein transport vesicles (STVs). Unlike surface mobility, intracellular transport of βNrxn(+) STVs was faster than that of αNrxns, but both depended on the microtubule motor protein KIF1A and neuronal activity regulated the velocity. Large spontaneous fusion of Nrxn(+) STVs occurred simultaneously with synaptophysin on axonal membranes mostly outside of active presynaptic terminals. Surface Nrxns enriched at synaptic terminals where αNrxns and Nxph1/αNrxns recruited GABAAR subunits. Therefore, our results identify regulated dynamic trafficking as an important property of Nrxns that corroborates their function at synapses. SIGNIFICANCE STATEMENT: Synapses mediate most functions in our brains and depend on the precise and timely delivery of key molecules throughout life. Neurexins (Nrxns) are essential synaptic cell adhesion molecules that are involved in synaptic transmission and differentiation of synaptic contacts. In addition, Nrxns have been linked to neuropsychiatric diseases such as autism. Because little is known about the dynamic aspects of trafficking of neurexins to synapses, we investigated this important question using single-molecule tracking and time-lapse imaging. We identify distinct differences between major Nrxn variants both in surface mobility and during intracellular transport. Because their dynamic behavior is highly regulated, for example, by different binding activities, these processes have immediate consequences for the function of Nrxns at synapses. SN - 1529-2401 UR - https://www.unboundmedicine.com/medline/citation/26446217/Regulated_Dynamic_Trafficking_of_Neurexins_Inside_and_Outside_of_Synaptic_Terminals L2 - http://www.jneurosci.org/cgi/pmidlookup?view=long&pmid=26446217 DB - PRIME DP - Unbound Medicine ER -