The construct contained the Tcf3 gene in which the stop codon had been converted into a BamH1 restriction site by site-directed mutagenesis. The entire coding region of enhanced green fluorescent protein (EGFP) inserted in-frame into this BamH1 site. A PGKneo positive selection cassette was inserted downstream of the Tcf3 gene, and a PGK-driven Diphtheria Toxin gene was inserted outside the homologous regions for as a negative selection marker. Mice express functional Tcf3 as well as EGFP in hematopoietic stem cells, B lineage cells and erythroid lineage cells in bone marrow, as well as in peripheral B1 and B2 lineage B cells. (J:88032)