Powerful molecules: new use for miRNA discovered Johns Hopkins News-Letter, MD, February 22, 2007 A new study has illuminated the role of tiny snippets of the genetic material RNA in the development of blood stem cells into mature red and white blood cells. These findings offer a glimpse into a still poorly understood means of regulating cell development. ......... By examining miRNA-mRNA interaction predictions from the database, the scientists were able to sort the miRNA from blood stem cells into three categories, based on when they affect blood cell differentiation. The first group of miRNAs can inhibit proteins that cause initial differentiation of blood stem cells, which stops production of all types of blood cells. The second group of miRNAs can inhibit the differentiation of one general category or set of similar blood cells. The final group consists of miRNAs that inhibit production of only on one specific type of cell, such as red blood cells.