PROLIFERATION AND DIFFERENTIATION OF FETAL-RAT PULMONARY EPITHELIUM IN THE ABSENCE OF MESENCHYME

Previous studies have shown that pulmonary mesenchyme is required to m aintain epithelial viability and to support branching morphogenesis an d cytodifferentiation, We have examined whether pulmonary mesenchyme c an be replaced by a medium containing a combination of soluble factors , Day 13-14 fetal rat distal lung epithelium was enzymatically separat ed from its mesenchyme, enrobed in EHS tumor matrix, and cultured for 5 d in medium containing concentrated bronchoalveolar lavage, EGF, aci dic fibroblast growth factor, cholera toxin, insulin, and FBS (TGM), o r in control medium containing only FBS, After 5 d in culture, marked growth and morphological changes occurred in epithelial rudiments cult ured in TGM, whereas no changes were seen in controls, [H-3]Thymidine incorporation and nuclear labeling indices during the last 24 h of cul ture confirmed that epithelial rudiments cultured in TGM had significa nt proliferative capacities, Evaluation of surfactant protein gene exp ression by Northern analysis, in situ hybridization, and immunocytoche mistry demonstrated that distal lung epithelial differentiation progre ssed in TGM, Ultra-structural analysis demonstrated that fetal distal lung epithelium cultured in TGM contained lamellar bodies and deposite d a basal lamina, These results are the first demonstration that susta ined proliferation and differentiation of glandular stage distal pulmo nary epithelium can proceed in the absence of mesenchyme.