The role of serum in the epithelial outgrowth of mouse skin explants.

An experimental system is described which facilitates the measurement of epithelial outgrowth in vitro. Using this sytem the properties of the serum component supporting epithelial spread have been studied. It has been found that appreciable epithelial outgrowth occurs in concentrations of cow serum greater than 0.5% and that maximal outgrowth occurs at concentrations of 1% or greater. Only minimal outgrowth is apparent during the first day of culture. The lack of epithelial outgrowth in the absence of serum is not due to reduced cell viability since replacing serum after 3 days leads to cellular outgrowth. Though this activity is found in several sera studied (cow, fetal calf, human, horse, mouse and chicken), there are considerable quantitative differences between species. Epithelial cell outgrowth does not occur in the presence of medium plus bovine fibrin, serum albumin or thrombin. The serum component is heat labile and non-dialysable. It appears to be needed continuously and does not require DNA synthesis for its effect.