Decreased Hematopoiesis in miR29ab1 Deficient Mice
Reem Aboomar, Stephanie Saridakis, Ramasamy Santhanam, Jason R O'Rourke, Frederick Racke, Ramiro Garzon, Eric N Olson, Carlo M Croce, Stefan Costinean. The Ohio State University, Columbus; University of Texas Southwestern Medical Center, Dallas
Background: MicroRNAs (miRs) are small noncoding RNAs that play a major role in the gene posttranscriptional regulation. Since their discovery they have been linked to numerous physiological and pathological processes. In 2002 miR15 was found downregulated in 65% of analyzed chronic lymphocytic leukemia cases. Later, miR 29b was found downmodulated in acute myeloid leukemia.
Design: We decided to investigate the consequences of miR29b downregulation in genetically modified mice. We used cre-loxP technology to generate conditional knockouts (ko) with general deletion. We deleted separately the miR29ab1 and miR29b2 clusters and we crossed the two types of ko's in order to obtain the double ko, miR29ab1/b2c with complete deletion of miR29b. The mice were followed for two years. Mice were analyzed histologically. Cell blood counts were done periodically. Flow cytometry, colony forming assays and bone marrow transplantation were used to assess the hematopoiesis.
Results: The miR29ab1 ko's were normal at birth except for a skewed Mendelian ratio for the homozygous (10% percentage of born homozygous instead of 25% expected percentage). The homozygous have half the lifespan compared with wild type counterparts. The histology of ko spleens revealed a global decrease in hematopoiesis, especially in the myeloid lineage (half the levels of wild type mice). Colony forming assays performed at different ages confirmed a marked decrease of hematopoietic stem cells. Flow cytometry showed a dramatic increase of the c-kit positive population in the bone marrow of the ko animals. Mir29b2c did not exhibit any of these changes indicating that the alterations are miR29ab1 specific. We are now conducting bone marrow transplants to ascertain the diminished capacity of miR29a ko's to repopulate the bone marrow in irradiated mice. Of interest, mir29 double ko mice have a short life span, of only 1 month ± 1 week.
Conclusions: Based on the present results we conclude that miR29ab1 ko's have decreased hematopoietic stem cell population compared to the wild types and that miR29ab1 might have an important role in the maintenance of this cell population. Also, miR29 genes might regulate immunity and life span, since both miR29ab1 and miR29ab1/b2c ko's seem to have markedly decreased life spans.
Tuesday, March 20, 2012 1:30 PM
Platform Session: Section G, Tuesday Afternoon