Leptin stimulates erythroid and myeloid colonies. Hematopoietic cells from (A) ES-derived embryoid bodies (d6), (B) murine d13 fetal liver, (C) adult bone marrow from normal and db mutant mice, (D) adult murine bone marrow, or (E) adult human bone marrow are cultured in methylcellulose colony assays containing leptin (L) and/or steel factor (SLF ). For adult marrow assays all groups contained saturating levels of rhEPO (2 U/mL). Sex- and age-matched marrow from normal and C57BL/6J db/db mice were used for the experiments in (C). Each graph is representative of data from three experiments. NR, no response.