JAK2 and leukemia: Reports indicate that JAK2 is negatively regulated by the trxG H3K9 methyltransferase G9a in leukemia cells, and G9a knockdown directly increases JAK2-mediated phosphorylation of histone H3 on Tyr 41 (Y41) by inducing JAK2 expression, suggesting that G9a plays an upstream regulatory role in JAK2-H3Y41P-HP1α -mediated leukemogenesis (Son et al., 2012).