β-galactosidase of ROSA26 mice is a useful marker for detecting the definitive erythropoiesis after stem cell transplantation

Background. Hematopoietic reconstitution after stem cell transplantation has been analyzed by using stem cells of Ly5 congenic mice. However, the early erythropoiesis has never been analyzed because this marker is not expressed on all of the erythroid lineage cells. The transgenic mouse expressing /3-galactosidase (β-gal) or green fluorescent protein (GFP) has been reported. Using these markers, we analyzed the early erythropoiesis after stem cell transplantation. Methods. The β-gal activity and GFP were examined in the hematopoietic cells of ROSA26 and GFP transgenic mice, respectively, by flow cytometry. The primitive hematopoietic stem cell fraction (Lin - c-kit + Sca-1 + ) in bone marrow (BM) cells of ROSA26 mice was transferred into lethally irradiated mice. The kinetics of hematopoietic reconstitution was analyzed in the BM and spleen after transplantation. Results. The β-gal activity, but not the GFP and Ly5, was detected in all of the erythroid (TER119 + ) cells. The (3-gal activity was also detected in the donor-derived myeloid (Mac-1 + ), B lymphoid (B220 + ), and T lymphoid (Thy-1 + ) cells in the BM and spleen after stem cell transplantation. The kinetics of the hematopoietic reconstitution demonstrated that early erythroid (TER119 low CD71 med ) cells were developed in the BM and spleen within 2 days after transplantation before development of proerythroblasts (TER119 + CD71 high ), and that massive erythropoiesis and myelopoiesis were observed in the spleen until 2 and 4 weeks after transplantation, respectively. Conclusions. The β-gal of ROSA26 mice can be a useful marker to identify the donor-derived hematopoietic cells, including early erythroid cells, and the first major wave of erythropoiesis occurring in the spleen after stem cell transplantation.