Dermal fibroblast-derived growth factors restore the ability of ss(1) integrin-deficient embryonal stem cells to differentiate into keratinocytes

Embryonal stem (ES) cells that are homozygous null for the beta (1) integri n subunit fail to differentiate into keratinocytes in vitro but do differen tiate in teratomas and wild-type/beta (1)-null chimeric mice. The failure o f beta (1)-null ES cells to differentiate in culture might be the result of defective extracellular matrix assembly or reduced sensitivity to soluble inducing factors. By culturing embryoid bodies on dead, deepidermized human dermis (DED) we showed that epidermal basement membrane did not induce bet a (1)-null ES cells to undergo keratinocyte differentiation and did not sti mulate the differentiation of wild-type ES cells. Coculture with epidermal keratinocytes also had no effect. However, when human dermal fibroblasts we re incorporated into DED, the number of epidermal cysts formed by wild-type ES cells increased dramatically, and small groups of keratin 14-positive c ells differentiated from beta (1)-null ES cells. Fibroblast-conditioned med ium stimulated differentiation of K14-positive cells in wild-type and beta (1)-null embryoid bodies. Of a range of growth factors tested, KGF, FGF10, and TGF alpha all stimulated differentiation of keratin 14-positive beta (1 )-null cells, and KGF and FGF10 were shown to be produced by the fibroblast s used in coculture experiments. The effects of the growth factors on wild- type ES cells were much less pronounced, suggesting that the concentrations of inducing factors already present in the medium were not limiting for wi ld-type cells. We conclude that the lack of beta (1) integrins decreases th e sensitivity of ES cells to soluble factors that induce keratinocyte diffe rentiation. (C) 2001 Academic Press.