Stimulation-Induced Differential Redistributions of Clathrin and Clathrin-Coated Vesicles in Axons Compared to Soma/Dendrites

Abstract

Clathrin-mediated endocytosis plays an important role in the recycling of synaptic vesicle in presynaptic terminals, and in the recycling of transmitter receptors in neuronal soma/dendrites. The present study uses electron microscopy (EM) and immunogold EM to document the different categories of clathrin-coated vesicles (CCV) and pits (CCP) in axons compared to soma/dendrites, and the depolarization-induced redistribution of clathrin in these two polarized compartments of the neuron. The size of CCVs in presynaptic terminals (~40 nm; similar to the size of synaptic vesicles) is considerably smaller than the size of CCVs in soma/dendrites (~90 nm). Furthermore, neuronal stimulation induces an increase in the number of CCV/CCP in presynaptic terminals, but a decrease in soma/dendrites. Immunogold labeling of clathrin revealed that in presynaptic terminals under resting conditions, the majority of clathrin molecules are unassembled and concentrated outside of synaptic vesicle clusters. Upon depolarization with high K+, label for clathrin became scattered among de-clustered synaptic vesicles and moved closer to the presynaptic active zone. In contrast to axons, clathrin-labeled CCVs and CCPs were prominent in soma/dendrites under resting conditions, and became inconspicuous upon depolarization with high K+. Thus, EM examination suggests that the regulation and mechanism of clathrin-mediated endocytosis differ between axon and dendrite, and that clathrrin redistributes differently in these two neuronal compartments upon depolarization.

Clathrin packets move in slow axonal transport and deliver functional payloads to synapses

“…As shown in the representative images (Figure 5F), immuno-gold particles were mostly seen around-and not within-SV clusters, and some gold particles were associated with vesicular structures resembling endosomes and cisternae (asterisk in Figure 5F, subpanel 2). Coated vesicles are rarely seen at synapses, as reported by previous EM studies (Heuser and Reese, 1973;Kononenko et al, 2014;Petralia et al, 2003;Tao-Cheng, 2020). Taken together, the super- (F) Immuno-gold EM of clathrin ( silver enhancement of nanogold particles).…”