Single cell RNA analysis uncovers the cell differentiation trajectories and functionalization for air breathing of frog lung

The evolution and development of vertebrate lungs have received extensive concerns for the significance in terrestrial adaptation. Amphibians possess the most primitive lungs among tetrapods, underscoring the evolutionary importance of lungs in bridging the transition from aquatic to terrestrial life. However, the intricate process of cell differentiation during amphibian lung development is still lacking. Using single cell RNA-seq, we identified 21 cell types in the developing lung of a land-dwelling frog (Microhyla fissipes). We elucidated that single type of alveolar epithelial cells (AECs) existed in amphibian and the diversity of AECs may correspond to the capacity for terrestrial adaptation in tetrapods. Based on pseudotime trajectories analysis, we revealed previously unrecognized developmental-specific transition cell states of epithelial and endothelial cells supporting the rapid morphogenesis of lung during metamorphic climax. We illustrated the cellular and molecular processes during lung functionalization. These findings uncover the cell differentiation trajectories and functionalization for air breathing of frog lungs and highlight the evolutionary peculiarity of the primitive lungs. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=180 SRC="FIGDIR/small/549571v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@d3188aorg.highwire.dtl.DTLVardef@f049feorg.highwire.dtl.DTLVardef@189f98borg.highwire.dtl.DTLVardef@15e3857_HPS_FORMAT_FIGEXP M_FIG C_FIG