Lysosomal and mitochondrial changes in lung alveolar epithelial cells upon Sendai virus infection. (A) Genetically labeled individual AT1 cells using Rtkn2^CreER in uninfected and 14 d after infection (dpi) with Sendai virus. As quantified for individual cells, AT1 cells of infected lungs in both AT2-containing and AT2-less regions have fewer but larger lysosomes. Mitochondria are minimally affected. Three images per condition were analyzed, with one to two AT1 cells per image as a result of sparse cell labeling and patchiness of the infection. Cells #1 and #2 are shown in this panel and Fig. S4, respectively. The organelle numbers are normalized by cell volume based on EGFP-α-Tubulin since mature AT1 cells are too large to be completely captured within even a thick section. *, P < 0.05; **, P < 0.001; ns, not significant (ordinary ANOVA with Tukey test; data are mean and standard deviation). Scale: 10 μm. (B) Genetically labeled AT2 cells using Sftpc^CreER in lungs 14 d after Sendai virus infection outside AT2-less regions. Compared with AT2 cells, a lineage-labeled AT1 cell (red mask) has characteristic numerous small lysosomes, supporting reorganization of subcellular structures as AT2 cells differentiate into AT1 cells. AT2 cells are outlined with dashes; AT1 cell organelles are marked by arrowheads. Scale: 10 μm. See also Video 7.