Collagen synthesis during epitheliomesenchymal interactions

The synthesis of collagenous proteins was examined in transfilter cultures of mouse embryonic mesenchyme and epithelium. Tissues were analyzed for polypeptide proline and hydroxyproline derived from proline- 3H. Mesenchyme grown in the presence or absence of epithelium synthesized appreciable amounts of collagen, although radioactive collagen was not detected in epithelia grown in the absence of mesenchyme. The formation of epithelial collagen was investigated in transfilter cultures by continuous labeling of the rudiments and after mesenchymal labeling. After continuous labeling, pancreatic and salivary epithelia grown in association with salivary mesenchyme contained radioactive collagen. Compared to those exposed to continuous label, epithelia grown transfilter from labeled mesenchyme showed a 6-fold increase in the relative amount of radioactive collagen. Salivary epithelia cultured transfilter from labeled mammary mesenchyme did not undergo morphogenesis, yet contained a similar amount of radioactive collagen as pancreatic and salivary epithelia grown transfilter from labeled salivary mesenchyme. The label in the epithelia could not be accounted for by the transfer of free proline- 3H from the mesenchyme. The results suggest that collagen synthesized in the mesenchyme is transported across the filter to the epithelium, but that the transfilter passage of collagenous proteins is not dependent upon epithelial morphogenesis. Developing epithelia were shown to regulate the amount of mesenchymal collagen. The relative amount of radioactive collagen in salivary mesenchyme cultured transfilter from pancreatic or salivary epithelium was significantly greater than in mesenchyme grown in the absence of epithelium. Equivalent quantities of polypeptide hydroxyproline were found in extracts of the nutrient medium from each culture type. No difference in the amount of radioactive collagen was detected between mammary mesenchyme cultured in the presence or absence of salivary epithelium.