Definitive but not primitive hematopoiesis is impaired in jumonji mutant mice

A novel gene, jumonji was identified by a mouse gene trap strategy. The jumonji gene encodes a protein containing a putative DNA binding domain. The mice homozygous for jumonji gene with a BALB/cA genetic background show hypoplasia of the fetal liver and embryonic lethality, suggesting impaired hematopoiesis. In the peripheral blood of jumonji mutant embryos, the number of fetal liver-derived definitive erythrocytes, but not yolk sac-derived primitive erythrocytes, showed a marked reduction, suggesting that jumonji mutants die of anemia. The defects of definitive erythrocytes in jumonji mutants seemed to be caused by a decrease in the numbers of multiple hematopoietic progenitors including colony-forming unit-spleen (CFU-S) in the fetal liver. However, hematopoietic stem cells (HSCs) in the fetal liver of jumonji mutants could reconstitute the hematopoietic system of lethally irradiated recipients. In the fetal liver, the jumonji gene is expressed in fibroblastic cells and endothelial cells, but not in Lin-/c-Kit+/Sca-1(+) cells known to include HSCs. These results suggest that an environmental defect induce the impaired hematopoiesis in the fetal liver of jumonji mutant embryos.