To examine the filamentous structure of poly(GA) proteins in mouse brain, immunoEM was performed as previously described52 (link). Thin sections were pretreated with sodium citrate buffer, pH 6 at 90–95 °C for 10 min before immunolabeling. Rabbit polyclonal antibody to poly(GA) (1:150 in PBS) was used as the primary antibody, and goat anti-rabbit IgG conjugated with 18 nm colloidal gold particles (1:20, Jackson ImmunoResearch Laboratories) was used as the secondary antibody. Thin sections stained with uranyl acetate and lead citrate were examined with a Philips 208S electron microscopy (FEI) fitted with a Gatan 831 Orius charge-coupled device (CCD) camera (Gatan). Digital images were processed with Adobe Photoshop CS5 software.