Hemidesmosomes regulate epidermal differentiation during embryogenesis.

In skin epidermis, integrins mediate adhesion of basal keratinocytes to the underlying basement membrane. While high expression of integrins has been correlated with stemness, there is limited direct evidence that integrins mediate keratinocyte retention within the basal layer. Here, we generate mosaic, epidermal-specific loss of integrin-β4 (encoded by Itgb4) or its ligand, laminin-α3β3ɣ2 (Lama3), using an in utero lentiviral-mediated approach. Although mutations in these genes cause postnatal skin blistering in mice and humans, we observe no evidence of epidermal-dermal separation embryonically. Despite no obvious alterations to apicobasal polarity, Itgb4-deficient basal cells show mild defects in oriented cell divisions, with increased oblique divisions and altered telophase correction. However, differentiation via cellular delamination-where basal keratinocytes lose adhesion to the underlying basement membrane and transit into the suprabasal layer-is elevated upon Itgb4 and Lama3 loss. Notably, hyperactive Notch signaling both decreases integrin-β4 expression and increases delamination. These findings conclusively demonstrate a causal role for hemidesmosomes in regulating epidermal differentiation through both mitotic and non-mitotic mechanisms and shed additional light on the programs regulating delamination.