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MicroRNAs control the expression of genes. Some microRNAs, called oncomiRs, powerfully affect expression of oncogenes and tumor suppressor genes.
MicroRNA-21 (miR-21) is expressed at high levels in many animal and human tumors. A team from Yale University genetically engineered mice to express miR-21 that could be turned on or off experimentally. Within 2 months, newborn mice in which miR-21 was produced developed lymphadenopathy, splenomegaly, anemia, bone marrow invasion by malignant lymphocytes, and vertebral tumors that caused spinal cord compression and limb paresis. The malignant cells carried markers of B-cell lymphoblastic lymphomas and leukemias. Siblings of these mice, in which miR-21 was not produced, had no evidence of lymphoma o…