Fig. 1

Schematic of the cell culture process for human stratified and columnar epithelial stem cells on a 3T3 mouse feeder layer. For stratified epithelial stem cells, they are isolated from biopsy or surgical specimens are plated on a 3T3 layer for a long-term culture. For columnar epithelial stem cells, they are plated on a 3T3 layer with defined factors which are essential for stem cell growth and maintenance. Morphologically immature colonies (packed colonies with small cells) of epithelial stem cells are mechanically picked-up for further homogeneous expansion. In the ALI culture, the cells undergo differentiation into mature cell types in a Transwell