Cell-type–specific ERV expression in primary cells. Cell-type–specific ERV expression in primary cells. (A) Cell types and associated information for each sample used in the ERV analysis. (B) Histogram of the amount of reads attributed to each of the 3,220 ERV loci sorted in order of highest to lowest expressed ERVs for each cell type. For cell types with multiple samples, the average number of reads per locus was plotted. (C) Sum of all ERV reads per sample compared across cell types. For cell types with multiple datasets, the average and SEM are graphed. (D) Heatmap of ERVs that are expressed across indicated cell types. The 500 most varying ERVs were used for the analysis to reduce noise. Two-dimensional t-SNE analysis (E) and PCA (F) of ERVs expressed by indicated cell types using the same set of 500 ERVs as in D. t-SNE analysis was performed using a perplexity of 30 and maximum iteration of 1,000. Maria Tokuyama et al. PNAS doi:10.1073/pnas.1814589115 ©2018 by National Academy of Sciences