Regulation of CpG island promoters by the histone methyltransferase MLL2

MLL2 is a H3K4 specific HMT which vital for normal embryonic development in the mouse. Little is known on how MLL2 is recruited to its target genes and activates transcription. To gain insight into the molecular mechanism underlying MLL2 function, we focused on a known MLL2 target gene: Magoh2. This gene is controlled by a CpG island promoter and is ubiquitously expressed. Our results demonstrate that in the absence of MLL2, the Magoh2 promoter is methylated and Magoh2 is transcriptionally silenced. The Magoh2 promoter adopts the active conformation only in the presence of MLL2. Pol II is lost from the Magoh2 promoter in the absence of MLL2, resulting in Magoh2 down-regulation. We observed loss of H3K4me\(_3\)and H3K9ac and relocation of a nucleosome over the promoter, coinciding with the onset of DNA methylation. Use of ORB and a-amanitin demonstrated that neither transcription nor the presence of Pol II are required for the maintenance of H3K4me\(_3\). Magoh2 silencing can be overcome by re-introducing full-length MLL2. We investigated the role of MLL2 in haemopoiesis and demonstrated that MLL2 is vital for macrophage differentiation from embryoid bodies. MLL2 may be required for correct upregulation of Flk1 and generation of haem angioblast cells. When M//2 was deleted in haemangioblasts, the haemopoietic transcriptional program was perturbed suggesting that MLL2 may also play a role at this later developmental stage