A TRANSGENIC MARKER FOR MOUSE B-LYMPHOID PRECURSORS

Three lines of transgenic mice have been generated which express human CD25 under the control of the 722-base pair region located immediatel y 5' of the precursor (pre)-B-cell-specific lambda 5 gene. All three s trains express human CD25 in parallel to endogenous lambda 5 on pre-B cells, but not on mature B lymphocytes or other blood cell lineages. H igh expression of human CD25 on B lineage cells of transgenic mice has allowed the identification of a new B220(+)CD19(-)lambda 5(+) precurs or of the B220(+)CD19(+)lambda 5(+) c-kit(+) pre-BI cells. Both types of precursors are clonable on stromal cells in the presence of interle ukin-7. The CD19(-) precursors have a sizeable part of their immunoglo bulin heavy chain gene loci in germline configuration, while the CD19( +) pre-BI cells are predominantly DJ(H) rearranged. The results indica te that random integration of the 722-bp 5' region of the lambda 5 gen e into the mouse genome confers tissue and differentiation stage-speci fic expression of a transgene.