Spatiotemporal pattern of expression of the BRE-eGFP reporter during lung development Previous studies utilizing two independent canonical BMP pathway reporter mouse lines, one harboring a BRE-eGFP [33] and another harboring a BRE-lacZ allele [39] have demonstrated expression of the BRE-eGFP and BRE-lacZ reporters respectively in the epithelium of trachea and primary-bronchi already at around E10-E12.5. To extend these findings and map in detail the spatiotemporal pattern of canonical BMP signaling in the lungs, we collected lung tissues from the BRE-eGFP reporter mice at embryonic days E11, E12, E13.5, E14.5, E16, E17.5, E19.5 and postnatal days 1, 15 and 2 months and analyzed tissue sections for eGFP expression. Our analysis demonstrated that the BRE-eGFP reporter was active already at E11, reached maximal levels around birth, thereafter declining to minimal levels in the adult ( Figure 1 and Figure S1 ).