Lung morphogenesis is a well orchestrated,tightly regulated process that undergoes branching morphogenesis and alveologenesis.Matricellular protein Follistatin like-1 (Fstl1) has multiple functions in the developmental lung and the homeostasis of adult lung.We previously reported that Fstl1-deficient mice displayed septal hypercellularity and end-expiratory atelectasis resulting in neonatal lethality.