Isoforms of ΔNp63 and the migration of ocular limbal cells in human corneal regeneration

The p63 gene generates transactivating and N-terminally truncated transcripts (DeltaNp63) initiated by different promoters. Alternative splicing gives rise to three different C termini, designated alpha, beta, and gamma. In the ocular epithelium, the corneal stem cells, which are segregated in the basal layer of the limbus, contain the alpha isoform but not beta or gamma. Holoclones derived from the limbus are rich in alpha, meroclones contain little, and paraclones contain none. In normal resting corneal epithelium, p63 of all isoforms is absent. Upon corneal wounding, cells originating from the limbus and containing alpha migrate progressively through the epithelium of the peripheral and central cornea. In the absence of an attached limbus, no alpha isoform appears in the corneal epithelium. When migrating cells containing the alpha isoform appear in the wounded corneal epithelium, they are confined to the basal layer, but the suprabasal cells, not only of the cornea but of the limbus as well, contain mRNA encoding beta and gamma. These data support the concept that the alpha isoform of p63 is necessary for the maintenance of the proliferative potential of limbal stem cells and their ability to migrate over the cornea. The beta and gamma isoforms, being suprabasal and virtually absent from the resting limbus, are not stem cell markers but are likely to play a role in epithelial differentiation specifically during the process of corneal regeneration.