Transplanted bone marrow cells give rise to BMP4^R cells in the recipient spleen. WBB6F1 Kit^W/Wv mice were transplanted with C57BL/6 donor bone marrow cells or spleen cells, and the development of stress BFU-E was assayed. (A) Analysis of stress BFU-E in the spleens of transplanted mice after transplantation with bone marrow cells (left) or spleen cells (right). (Top graphs) Total BFU-E observed after spleen cells were plated on indicated days in media containing Epo + IL-3. (Bottom graphs) Stress BFU-E observed on the indicated days when spleen cells were plated in media containing Epo or Epo + BMP4 as indicated. (B) Analysis of stress BFU-E in the bone marrow of transplanted mice after transplantation of bone marrow cells (left) or spleen cells (right). (Top graphs) Total BFU-E observed after spleen cells were plated on indicated days in media containing Epo + IL-3. (Bottom graphs) Stress BFU-E observed on the indicated days when spleen cells were plated in media containing Epo or Epo + BMP4 as indicated. For each time point, 3 recipient mice were analyzed. Significant differences are indicated in the figure.