Neonatal activation of BRAF^V600E through the expression of Tyr::Cre^ERT2 upon 4OHTx treatment drives aberrant proliferation of lung cells.

(A) Schematic representation of mouse treatment and expressed proteins. (B) Representative images of Cre-recombinase staining in 4-days-old wild type (WT, n = 3) and Tyr::Cre^ERT2; Braf^CA/+ (n = 3) mice lungs treated with 4OHTx. Bars 80 µm. (C) Anti-p-ERK1/2 staining of untreated (−4OHTx) and treated (+4OHTx) 4-days-old Tyr::Cre^ERT2; Braf^CA/+ mice lungs. (D) Schematic representation of the genetic strategy to identify tyrosinase-promoter driven Cre-recombinase lung expressing cells. Representative images of EYFP, SP-C and CC10 expressing cells in Tyr::Cre^ERT2;ROSA-lsl-EYFP mice 3 days after 4OHTx treatment (n = 3 mice) are shown. Bars 80 µm. (E) Ki67 staining of histologically normal lungs in 8-days-old mice showed increased proliferation index in 4OHTx treated Tyr::Cre^ERT2; Braf^CA/+ mice compared to untreated. Bars 500 µm. Quantification of samples is shown below. 20X fields (n = 8 and n = 11 from 3 different untreated and 4OHTx treated mice respectively) were quantified. p-value was calculated performing Mann-Whitney’s test.