ERK activation and repopulating potential of

Rce1^−/− cells. (A) Bone marrow was collected 3 to 6 months after adoptive transfer, incubated under low (0.1%) serum conditions for 4 hours, and then stimulated with recombinant murine GM-CSF. The cells were lysed after 10 minutes, immunoprecipitated with an antibody against ERK, and phosphorylation of an Elk1 substrate was measured. (B) Percentages of peripheral blood leukocytes derived from Rce1^−/− (▪) and wild-type (●) 4 months after adoptive transfer with a standard population of CD45.1 competitor cells. Data are pooled from independent experiments and represent 3 to 6 recipients at each point.