Fig. 1.

Cell-ubiquitous structures observed in neurons. (A) Low-magnification cryo-EM image of a dissociated neuronal culture (see Box 1) grown on EM grid (bar, 500 nm). (B) 3D segmentation of a bouton from a dissociated neuronal culture containing plasma membrane (yellow), mitochondrion (red), microtubules (green), SER (orange), synaptic vesicles (light blue), dense core vesicles (dark blue) and other membranous compartments (grey). (C) A tomographic slice through an axon in human brain organoid. It contains several microtubules. In one of them, intraluminal particles are particularly evident. ER with an extremely narrow portion is marked with blue arrowheads and microtubule lumenal density by a orange arrowhead (bar, 50 nm). (D) Tomographic slice of an ER-plasma membrane contact sites (black arrows) in cultured neurons (bar, 200 nm). Inset. Higher-magnification tomographic slice of the ER–plasma membrane contact in the labeled region. The intermediate density between the ER and the plasma membrane is indicated by red arrowheads (bar, 50 nm). (E) 3D rendering of the tomogram depicted in D. (F) 3D rendering of an inclusion body in a neuron transfected with polyQ-huntingtin. ER membranes (red), polyQ-huntingtin fibrils (cyan), ribosomes (green), vesicles (white), and mitochondria (gold) (bar, 400 nm). Inset. Magnified view of a tomographic slice corresponding to the area labeled with a white rectangle showing polyQ-huntigntin fibrils (red arrowheads) decorated with globular densities (green arrowhead) (bar, 30 nm). Images are reproduced with permission from (Schrod et al., 2018) (A, B), (Hoffmann et al., 2021) (C), (Fernández-Busnadiego et al., 2015) (D, E) and (Bäuerlein et al., 2017) (F).