MAPK3 and breast cancer: To identify the embryonic origin of ventral root the Egr2-expressing BC cells that give rise to skin MCs, we performed genetic fate mapping analyses using Cre drivers targeting the NC (Wnt1Cre, Sox10Cre-Ert2) and the ventral neural tube (Olig2Cre), which are in the vicinity of BCs, in combination with Rosa26RTom or Rosa26RYFP Cre-inducible reporters.