MicroRNAs(miRNAs)are small inhibitory RNAs that regulate the translation of mRNAs.To investigate if this pathway is required for the dendritic cell(DC)development,we investigated the impact of ablating the RNase Ⅲ enzymes Drosha and Dicer within the hematopoietic system of bone marrow chimeric mice.These enzymes are central to miRNA biogenesis.We found that DC development(and the development of other myeloid populations)was completely ablated by Drosha deficiency,whereas Dicer deficiency only partially affected DC development.