Fig. 5.

Lung bud initiation occurs in serum-free culture. E8.5 wild-type and Flk-1^−/− mutant foreguts were cultured in medium with 20% KnockOut Serum Replacement for 4–5 days. NKX2-1 staining is detected in the lung buds (arrowheads) of both wild-type (A, A’) and Flk-1^−/− (B, B’) explants cultured in the KnockOut serum replacement. Endothelial cells are marked by PECAM-1 expression (A, B). NKX2-1-positive cells representing thyroid progenitor cells are distinguished by their co-staining with PAX8 (A, A”, B, B”). Since neural tissue was removed from the embryos prior to their being placed in culture, NKX2-1-positive, PAX8-negative cells represent lung progenitors. Scale bars =100 µm. N >5 individual explants from 2 independent experiments.