MAPK1 and neoplasm: In contrast to the BRAFCA/+Mx1cre/+ strain that turns on BRAF(V600E) in hematopoietic stem cells (henceforth referred as HSCVE strain), these strains constitutively expressed BRAF(V600E) that activates ERK signaling with loss of individual tumor suppressors only in B cells, as confirmed by PCR and immunoblots against phospo-ERK1/2, phospho-AKT, Trp53 and P27 in B cell lysates (Fig. 1B, C and S1).