ABSTRACT
The role of the microenvironment in morphogenesis and differentiation of tissues has been the subject of numerous investigations.1 There is considerable evidence that cells transduce signals not only from hormones and growth factors but also from adjacent cells and their surrounding extracellular matrix (ECM). Numerous attempts have been made to create ideal conditions so that cells grown in in vitro conditions may express and retain their phenotype. Cell monolayers cultured on plastic proved to be a useful model to elucidate the flow of information from DNA to a specific protein. However, epithelial cells proliferate but do not fully differentiate when grown on plastic. Fibroblasts proliferate into two-dimensional monolayer cultures; however, this is a nonphysiological environment. These cells in vivo never show a tendency for confluency except during early embryogenesis, wound healing, and following neoplastic transformation. The normal environment for fibroblasts and related mesenchymal cells is the ECM that they help synthesize. The specificity of this ECM varies depending on the function of the tissue, that is, skin, cartilage, bone, etc.
