DIFFERENTIATION OF EMBRYONAL STEM-CELLS INTO KERATINOCYTES - COMPARISON OF WILD-TYPE AND BETA(1) INTEGRIN-DEFICIENT CELLS

beta(1) Integrins are known to regulate terminal differentiation and m orphogenesis in the adult epidermis. We have investigated their role i n the embryonic development of keratinocytes by comparing the differen tiation of wild-type and beta(1)-null mouse embryonal stem (ES) cells. By 12-15 days in culture, differentiation of embryonic or simple epit helial cells occurred in both ES cell populations, as detected by expr ession of keratins 8, 18, and 19. From 21 days, expression of keratins 10 and 14 and of the cornified envelope precursor involucrin indicate d that some of the wild-type cells had differentiated into keratinocyt es. In contrast, keratinocyte markers were not expressed in beta(1)-nu ll cultures. The beta(1)-null cells failed to express the alpha(2) and alpha(3) integrin subunits on the cell surface, consistent with the a ssociation of these alpha subunits with beta(1). Furthermore, alpha(6) and beta(4) expression was reduced in the beta(1)-null cultures. Alth ough beta(1)-null ES cells failed to undergo differentiation into kera tinocytes in vitro, they did form keratinocyte cysts expressing alpha( 6) beta(4), keratins 1 and 14, and involucrin when allowed to form ter atomas by subcutaneous injection in mice; furthermore, beta(1)-null ke ratinocytes were found in the epidermis oi a wild-type/beta(1)-null ch imeric mouse. As judged by immunofluorescence microscopy, extracellula r matrix assembly was severely impaired in beta(1)-null ES cell cultur es, but not in the teratomas or chimeric mouse skin. We therefore spec ulate that the failure of beta(1)-null cells to differentiate into ker atinocytes in vitro may reflect an inability to assemble a basement me mbrane. (C) 1996 academic Press, Inc.