As the majority of eGFP pos cells did not express the marker for secretory airway epithelium (CC10), their possible relationship to ciliated airway epithelial cells was investigated by staining with antibodies for Foxj1 a ciliated cell specific differentiation marker. As shown in Figure S6 , a remarkably small portion of eGFP pos cells were FoxJ1 pos (yellow-arrows in Figure S6 ).