Normal Epidermal Basal Cell Behavior in the Absence of Basement Membrane

The definitive role of the basement membrane complex adjacent to epithelial cells has not been established for developing systems. Speculation based on its position and properties of permeability to molecules of various size (1, 2) has led to the idea that the basement membrane is an important factor in mediation of extrinsic cues to developing epithelial cells (3). I t is unknown whether the basement membrane must be present in order for normal cell behavior to proceed. Embryonic chick epidermis possesses a basement membrane below its columnar, mitotically active basal cells (4). Such epidermis can be freed from the adjacent dermis by trypsin-pancreatin treatment and cultured in vitro on Millipore filters (5, 6). During such treatment, fixable basement membrane materials are removed (5). When cultured in the presence of protein-free, defined chemical nutrients, the basal cells flatten and become mitotically quiescent after about 10 hr (7). In the presence of 20% by volume of chick embryo juice in the medium (6) or with dermis placed on the opposite side of the filter (5), the cells retain their normal orientation and activities. Under these