EPITHELIAL MARKER GENES ARE EXPRESSED IN CULTURED EMBRYONIC RAT LUNG AND IN-VIVO WITH SIMILAR SPATIAL AND TEMPORAL PATTERNS

Explants of embryonic lung are often used to characterize lung growth, bronchial tree pattern, and cell differentiation. Most investigators culture lungs for 3-7 days in defined media lacking, e.g., added growt h factors or hormones. If growth and differentiation are comparable to that in vivo, these cultures show considerable promise for identifyin g developmental regulatory molecules and target genes, and for elucida ting molecular responses. We used in situ hybridization and RT-PCR to compare times and sites of expression of mRNAs of six epithelial genes in cultured and uncultured fetal rat lungs. These genes, expressed in distal lung of adult rats, are surfactant proteins (SP) A, B, and C; LAR, a receptor-type tyrosine phosphatase; Clara cell secretory protei n (CC10, CCSP); and T1 alpha. SP-A, SP-B, LAR, and CC10 are expressed by both Clara and Type II cells in adult animals. SPC and Tla are uniq ue markers for Type II and Type I cells, respectively. SPC, LAR, and T 1 alpha are expressed before the lung is explanted (Day 13.5); SPA, -B , and CC10 mRNAs are first detected later. The onset of expression is similar in vivo and in vitro. Although the patterns of expression diff er for each mRNA, their sites of expression in culture match those in vivo relative to the bronchial tree. The explanted embryonic lung appe ars to be an excellent experimental model.