Mir-196b expression enhances colony formation and partially blocks hematopoietic progenitor cell differentiation. (A,B) Serial replating myeloid colony assay using c-Kit⁺ bone marrow cells. Cells were transduced with retroviruses producing mir-196b construct or with an empty vector and plated in methylcellulose with 2 different cytokine mixes. The number of colonies (A) and colony and cell morphology (B) at 1 and 4 weeks are shown. Only mir-196b–expressing cells are able to form colonies at the fourth week. Scale bars on cytospin pictures represent 10 μm in top panel and 25 μm in bottom panel. (C) Representative FACS profiles of in vitro–differentiated bone marrow cells. After 1 week of growth and selection in methylcellulose, mir-196b or vector-expressing bone marrow cells were plated on the OP9 cell line in the presence of GM-CSF or IL-7/Flt3L. After 5 days, expression of CD117 and CD11b (top panels, cells on GM-CSF) or B220 (bottom panels, cells on IL-7/Flt3L) was determined. Under both conditions, overexpression of mir-196b causes a partial block in differentiation.