Lin neg -EpCAM pos -Sca1 low cells cultured in this way, in agreement with previous reports [58] , gave rise primarily to large cystic epithelial colonies and Lin neg -EpCAM pos -Sca1 neg cells gave rise almost exclusively to smaller compact epithelial colonies ( Figure 7E ). The clonogenic capacity of both Sca1 low and Sca1 neg cells correlated with the expression levels of the BRE-eGFP reporter with the corresponding eGFP high populations exhibiting highest clonogenic capacity ( Figure 7F ). Previous studies have suggested that cystic colonies derived from Lin neg -EpCAM pos -Sca1 low cells contain progenitors of airway epithelial cells (Muc5Ac pos ), whereas, the compact colonies derived from Lin neg -EpCAM pos -Sca1 neg cells contain primarily SpC pos alveolar progenitors [58] . Consistently, as shown in Figure 7G , whereas all compact colonies derived from the Sca1 neg subpopulations exhibited a similar SpC pos -Muc5Ac neg staining pattern, the large cystic colonies derived from the Sca1 low subpopulations exhibited a more heterogeneous pattern of staining with approximately half of them expressing Muc5Ac and half of them expressing SpC.