(f) Immunohistochemistry for IAP-gag visualized the presence of ERV proteins in the cortex of Emx1-Cre/Trim28-KO animals. The distribution of IAP-gag was heterogenous among Trim28-KO neurons, where it was either accumulated in a low (#) or high (°) number of aggregate-like structures in the cytoplasm, or as weak homogenous staining throughout the cytoplasm (#) or not present at all (*). Scale bars: low magnification 75μm, high magnification 5 μm. 