Figure 1. Representation of corneal epithelial cell renewal dependent on proliferative symmetric mitosis of stem cells and their progeny. Stem cells and their progeny proliferate by horizontal, symmetric mitosis; in contrast, asymmetric cell division occurs only in cells that start stratifying and expressing the terminal phenotype. In this case, basal cells that initiate the expression of the terminal phenotype divide with a vertically oriented mitotic spindle. One of the daughter cells remains at the epithelial basal cell layer maintaining its proliferative abilities, and the other leaves the basal layer and enters the suprabasal compartment, becoming bigger, losing proliferative abilities, and becoming terminally differentiated (pink cells). In this model, the basement membrane (BM) modulates the self-renewal and proliferative abilities of stem cells and their progeny based on the its composition and structure. Green=limbal BM. Orange=peripheral and central cornea BM. Yellow=conjunctival BM. Blue arrows=stratification of terminally differentiating cells.