The Bmi-1^GFP knock-in/knockout allele has EGFP fused in-frame with the endogenous transcriptional start site of the Bmi-1 polycomb ring finger oncogene (Bmi1) locus; both abolishing endogenous gene function and placing EGFP expression under direction of the Bmi1 promoter/enhancer regions. EGFP expression (direct fluorescence) is highest in hematopoietic stem cell (HSC) populations and downregulated along with differentiation; recapitulating the expected expression pattern of endogenous Bmi-1. Specifically, EGFP fluorescence is significantly higher in the HSC-enriched KLS population (c-kit⁺lin^-Sca-1⁺) compared with other populations.

Mice heterozygous for the Bmi-1^GFP knock-in/knockout allele are viable, fertile, and phenotypically indistinguishable from wildtype littermate controls with respect to survival, hematopoietic cellularity, and lineage composition. Heterozygous bone marrow cells sorted via FACS into GFP^high and GFP^lo show that the Bmi-1 expression level in the GFP^high population is approximately 10-fold higher than that of the GFP^lo population; these Bmi-1^high cell populations are functional HSCs.

The donating investigator reports that mice homozygous for the Bmi-1^GFP knock-in/knockout allele die before birth or soon after they are born. In addition, homozygotes may be expected to exhibit the same phenotype as mice homozygous for other null mutations of this gene (decreased hematopoietic cell number, immune deficiency, neurological abnormalities, and posterior transformation).

These mice also harbor the Ptprc^b allele, CD45.2, of C57BL/6J origin rather than the alternate allele normally present in C57BL/Ka inbred mice. As CD45 is expressed on all adaptive and innate immune cells, this strain provides a unique cell surface marker that can be used to track lineage and phenotype of all hematopoietic donor derived or transferred cells.

In addition, these mice also harbor the Thy1.1 leukocyte alloantigen allele, Thy1^a, rather than the alternate allele normally present in C57BL/Ka inbred mice (as well as C57BL/6, C57BL/10, DBA/2, NOD, and BALB/c inbred mice). Thus, cell populations derived from these mutant mice can be distinguished from syngeneic host and other mice with the alternate allele via flow cytometry. The presence of Thy1^a serves as a marker for tracking donor cells in vitro.