Figure 7. Transfer of prion between infected astrocytes.

(a) PrP^Sc aggregates (red) are easily detected in green CTG-acceptor astrocytes after 24-co-culture with unlabeled 22L-astrocytes (co-culture). Shown for comparison are representative images of uninfected astrocytes (control) and astrocytes that have been cultured for 24 h in the presence of 24 h 22L-astrocyte conditioned medium (conditioned medium). GFAP is shown in blue. Scale bars: 10 μm. (b) Quantification of the percentage of astrocytes containing transferred PrP^Sc after 24 h co-culturing versus those grown in the presence of conditioned medium. **p = 0.0017 (c) Left: Z projections of 22L-infected astrocytes forming numerous PrP^Sc-containing intercellular connections, including TNTs (Insets). Right: Snapshots of orthogonal views (xyz cuts through the image) showing a slice through the TNT: PrP^Sc aggregates colocalize with endolysosomal vesicles within TNTs (white arrows), including lysosomes (Lamp1), early endosomes (EEA1) and endocytic recycling compartments (Vamp3). Images for Vamp3 and EEA1 have had their orientation rotated 90° and inverted for presentation purposes. Organelle markers: green, PrP^Sc: red, and the plasma membrane marker WGA: blue. Scale bars: 5 μm.