Abstract:
Overexpression of miRNA, miR-24, in mouse hematopoietic progenitors increases mono cytic/ granulocytic differentiation and inhibits B cell development. To determine if endoge nous miR-24 is required for hematopoiesis, we antagonized miR-24 in mouse embryonic
stem cells (ESCs) and performed in vitro differentiations. Suppression of miR-24 resulted in
an inability to produce blood and hematopoietic progenitors (HPCs) from ESCs. The pheno type is not a general defect in mesoderm production since we observe production of na scent mesoderm as well as mesoderm derived cardiac muscle and endothelial cells.
Results from blast colony forming cell (BL-CFC) assays demonstrate that miR-24 is not re quired for generation of the hemangioblast, the mesoderm progenitor that gives rise to
blood and endothelial cells. However, expression of the transcription factors Runx1 and Scl
is greatly reduced, suggesting an impaired ability of the hemangioblast to differentiate. Last ly, we observed that known miR-24 target, Trib3, is upregulated in the miR-24 antagonized
embryoid bodies (EBs). Overexpression of Trib3 alone in ESCs was able to decrease HPC
production, though not as great as seen with miR-24 knockdown. These results demon strate an essential role for miR-24 in the hematopoietic differentiation of ESCs. Although
many miRNAs have been implicated in regulation of hematopoiesis, this is the first miRNA
observed to be required for the specification of mammalian blood progenitors from
early mesoderm.
