Video 1.
Model for automatic cleansing of stratified squamous epithelia. Basal proliferative cells harboring an irreparable mutational burden (red nuclei; damaged nucleus), due to the induction of the mitotic checkpoints by the DDR, block mitosis (G2/M arrest). Basal cells are tightly packed within the tissue. When cells spend a long time in G2/M for DNA repair, they increase in size, lose adherence, and are pushed by more adherent proliferative neighbor cells about to divide, giving the typical mushroom appearance previously described (Régnier et al., 1986). Dividing cells do not have to be next to the mitosis-blocked cell to push a mitotically arrested cell upwards due to transmission of lateral forces. When a basal cell stratifies into the peribasal layer, it pushes other suprabasal cells above so that on the surface of the skin, a cell is detached (shedding). This automatic cell-autonomous mechanism might suffice in a steady-state epidermis or even upon UV light–induced DNA damage, to maintain the balance of the tissue.