Recombineering of the BAC clone RP23-99E8 containing the T (brachyury) locus generated a targeting vector designed to replace the stop codon of T and introduce sequences encoding the ERAV 2A peptide, a human histone H2B/EGFP fusion protein (protein is expressed in the cell nucleus), the Thosea asigna virus 2A peptide and cre/ERT2 fusion protein. A self-excising ACN cassette (containing the neo resistance marker) was also included. The vector was electroporated into ES cells for homologous recombination. Chimeras were generated from 3 independent clones (36, 41, and 44) and were bred to C57BL/6J females, with the ACN cassette self-excising during passage through the germline. The line derived from #41 was analyzed further.