Differentiation and Proliferation in vitro.

Abstract

In an earlier paper 1 the conditions were described under which undifferentiated sheets of epithelial cells became differentiated into a tissue which formed tubules. When pure strains of epithelial cells and fibroblasts were cultivated together in the same medium, it was found that the 2 cell types retained their individual characteristics indefinitely. 2 The connective tissue cells promptly surrounded the epithelial cells which arranged themselves into structures resembling glandular tissue, with distinct luminae. This same observation was made by Drew 3 in connection with skin epithelium and carcinoma cells. Drew stated that differentiation occurred only as the result of the interaction of 2 different tissues. However, one of us 1 has shown that differentiation is not necessarily dependent upon the interaction of other tissues. In order to obtain keratinization and tubule formation in cultures of pure epithelial cells, it is only necessary to refrain from cutting the culture through the center when transferring it from one medium to another. In other words, differentiation begins to take place as soon as the tissue becomes thick and in such a state that the central portion becomes badly nourished and poorly aërated. When epithelial cultures grow in membrane formation, the growth is rapid and extensive; when the tubular type of colonies appear, growth proceeds very slowly and the actual increase in mass is relatively small, although the outgrowing tubules may become of very considerable length.

The experiments, here to be described, deal with factors which, it is believed, play a very considerable role in the mechanism of differentiation. The material used consisted of a 6 months old strain of fibroblasts derived from bone, but from which all trace of the original tissue was very early eliminated by selection of only the new outgrowth at the time of transfer.