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Epithelial-fibroblastic organization in cultures grown from human embryonic kidney: its significance for morphogenesis in vivo.

The morphological behaviour of explants of human embryonic kidney has been studied in order to investigate the rules governing interactions between epithelial and fibroblastic cells from the same tissue. When the fragments are cultured, epithelia migrate out first and are followed, a few days later, by cables which grow out from the fragments and which are composed of multilayered fibroblasts. These cables extend through the epithelia to reach the substratum, to which they adhere. The epithelia maintain an upper surface free of spread fibroblasts and are unable to multilayer, although occasional rounded-up cells adhere to this surface. Fibroblasts, however, not only multilayer in the cables but can act as a substratum for epithelial cells which migrate on the cable surface. Fibroblasts and epithelia from kidney thus follow the same behavioural rules that govern the interactions between kidney epithelia and fibroblasts from different tissues. The suggestion that these rules derive from tissue differences and that cells from the same tissue are more tolerant of one another is not borne out. These observations and those reported by others are interpreted in terms of the functional properties of the cells in vivo. It is further pointed out that only those epithelia that maintain a free surface in vivo would be expected to show this property in vitro. Finally, the implications of cells with essentially the same properties generating more than one structure are considered.