Abstract
At mammalian glutamatergic synapses, most basic elements of synaptic transmission have been shown to be modulated by specific transsynaptic adhesion complexes. However, although crucial for synapse homeostasis, a physiological regulation of synaptic vesicle endocytosis by adhesion molecules has not been firmly established. The homophilic adhesion protein N-cadherin is localized at the peri-active zone, where the highly temperature-dependent endocytosis of vesicles occurs. Here, we demonstrate an important modulatory role of N-cadherin in endocytosis at near physiological temperature by synaptophysin-pHluorin imaging. Different modes of endocytosis including bulk endocytosis were dependent on N-cadherin expression and function. N-cadherin modulation might be mediated by actin filaments because actin polymerization ameliorated the knockout-induced endocytosis defect. Using super-resolution imaging, we found strong recruitment of N-cadherin to glutamatergic synapses upon massive vesicle release, which might in turn enhance vesicle endocytosis. This provides a novel, adhesion protein-mediated mechanism for efficient coupling of exo- and endocytosis.
Highlights
A variety of transsynaptic adhesion protein complexes have been molecularly characterized at mammalian CNS synapses, and are thought to have important specific roles in synapse formation, synapse function, and synaptic plasticity (Scheiffele et al, 2000; Schreiner et al, 2017; Südhof, 2018)
We investigated the functional roles of the synaptic adhesion molecule N-cadherin in both synaptic vesicle exoand endocytosis in cultured mouse cortical neurons
Synaptic vesicle endocytosis was quantified by two measures (Figure 1B): (i) by the amount of fluorescence decay at 90 s after the end of stimulation, and (ii) by the monoexponential decay time constant of the SypHy signal
Summary
A variety of transsynaptic adhesion protein complexes have been molecularly characterized at mammalian CNS synapses, and are thought to have important specific roles in synapse formation, synapse function, and synaptic plasticity (Scheiffele et al, 2000; Schreiner et al, 2017; Südhof, 2018). The mammalian N-cadherin transsynaptic adhesion complex at glutamatergic synapses is based on pre- and postsynaptic transmembrane N-cadherin proteins containing five extracellular cadherin domains (Takeichi, 2007; Benson and Huntley, 2012), which are interacting in cis and trans configurations (Brasch et al, 2012; Friedman et al, 2015). Previous studies of N-cadherin functions at the synapse using standard knockout approaches had been difficult, because constitutive N-cadherin knockout mice are lethal at early embryonic stages (Radice et al, 1997), and conditional N-cadherin knockout mice showed strongly impaired neuronal migration during cortex development leading to largely disorganized cortical structures (Kostetskii et al, 2005; Kadowaki et al, 2007)
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