IgH recombination detected upon culture of tamoxifen treated E2AER/ER pre-proB cells. DNA was analyzed for IgH V to DJ rearrangements from Day 8 cultured wild-type (WT), Rag1-/- (Rag) and E2AER/ER (ER) pre-proB cells using VH1 and JH4 primers. Cells were cultured in hormone-free media on S17 stromal cells with IL-7 and tamoxifen (T) or DMSO (D). V-DJ rearrangement products using VH1 family gene segments and JH4 are shown. WT and Rag were used as positive and negative controls, respectively. No products were detected when using dH2O as an additional negative control (data not shown). CD14 was used to demonstrate DNA loading. This result is representative of 4 independent nested PCR reactions.