Differentiation of Embryonal Stem Cells into Keratinocytes: Comparison of Wild-Type and β1Integrin-Deficient Cells

Abstractβ1Integrins are known to regulate terminal differentiation and morphogenesis in the adult epidermis. We have investigated their role in the embryonic development of keratinocytes by comparing the differentiation of wild-type and β1-null mouse embryonal stem (ES) cells. By 12–15 days in culture, differentiation of embryonic or simple epithelial cells occurred in both ES cell populations, as detected by expression of keratins 8, 18, and 19. From 21 days, expression of keratins 10 and 14 and of the cornified envelope precursor involucrin indicated that some of the wild-type cells had differentiated into keratinocytes. In contrast, keratinocyte markers were not expressed in β1-null cultures. The β1-null cells failed to express the α2and α3integrin subunits on the cell surface, consistent with the association of these α subunits with β1. Furthermore, α6and β4expression was reduced in the β1-null cultures. Although β1-null ES cells failed to undergo differentiation into keratinocytesin vitro,they did form keratinocyte cysts expressing α6β4, keratins 1 and 14, and involucrin when allowed to form teratomas by subcutaneous injection in mice; furthermore, β1-null keratinocytes were found in the epidermis of a wild-type/β1-null chimeric mouse. As judged by immunofluorescence microscopy, extracellular matrix assembly was severely impaired in β1-null ES cell cultures, but not in the teratomas or chimeric mouse skin. We therefore speculate that the failure of β1-null cells to differentiate into keratinocytesin vitromay reflect an inability to assemble a basement membrane