Experimental setup for identification of Hoxa9/Meis1 target genes. (A) Immunoblot of nuclear extracts from packaging cells used to produce pMSCV-HA-Hoxa9 and pMSCV-flag-Meis1 viruses. Control indicates cells transfected with empty vector. (B) Schematic representation of experimental outline. MLL-ENL-ERtm is a fusion of MLL-ENL with the ligand binding domain of a mutated estrogen receptor.³¹  MLL-ENL-ERtm is only active in the presence of 4-OHT.