Project description:The MLL1 histone methyltransferase gene undergoes many distinct chromosomal rearrangements to yield poor-prognosis leukemia. The remaining wild-type allele is most commonly, but not always, retained. To what extent the wild-type allele contributes to leukemogenesis is unclear. Here we show using rigorous, independent animal models that endogenous MLL1 is dispensable for MLL-rearranged leukemia. Potential redundancy was addressed by co-deleting the closest paralog, Mll2. Surprisingly, Mll2 deletion alone had a significant impact on survival of MLL-AF9-transformed cells and additional Mll1 loss further reduced viability and proliferation. We show that MLL1/MLL2 collaboration is not through redundancy but regulation of distinct pathways. These findings highlight the relevance of MLL2 as a drug target in MLL-rearranged leukemia and suggest its broader significance in AML. We used microarray to investigate the effect of Mll1 deletion on gene expression in LSC-enriched MLL-AF9 leukemia cells.
Project description:Neuronal histone H3-lysine 4 methylation landscapes are defined by sharp peaks at gene promoters and other cis-regulatory sequences, but molecular and cellular phenotypes after neuron-specific deletion of H3K4 methyl-regulators remain largely unexplored. We report that neuronal ablation of the H3K4-specific methyltransferase, Kmt2a/Mixed-lineage leukemia 1 (Mll1), in mouse postnatal forebrain and adult prefrontal cortex (PFC) is associated with increased anxiety and robust cognitive deficits without locomotor dysfunction. In contrast, only mild behavioral phenotypes were observed after ablation of the Mll1 ortholog Kmt2b/Mll2 in PFC. Impaired working memory after Kmt2a/Mll1 ablation in PFC neurons was associated with loss of training-induced transient waves of Arc immediate early gene expression critical for synaptic plasticity. Medial prefrontal layer V pyramidal neurons, a major output relay of the cortex, demonstrated severely impaired synaptic facilitation and temporal summation, two forms of short-term plasticity essential for working memory. Chromatin immunoprecipitation followed by deep sequencing in Mll1-deficient cortical neurons revealed downregulated expression and loss of the transcriptional mark, trimethyl-H3K4, at <50 loci, including the homeodomain transcription factor Meis2. Small RNA-mediated Meis2 knockdown in PFC was associated with working memory defects similar to those elicited by Mll1 deletion. Therefore, mature prefrontal neurons critically depend on maintenance of Mll1-regulated H3K4 methylation at a subset of genes with an essential role in cognition and emotion.
Project description:MLL1 translocations encode fusion proteins retaining the N-terminus of MLL1, which interacts with the tumor suppressor, menin. This interaction is essential for leukemogenesis, thus is a promising drug target. However, wild-type MLL1 plays a critical role in sustaining hematopoietic stem cells (HSCs), therefore disruption of an essential MLL1 cofactor would be expected to obliterate normal hematopoiesis. Here we show that rather than working together as a complex, menin and MLL1 regulate distinct pathways during normal hematopoiesis, particularly in HSCs and B-cells. We demonstrate the lack of genetic interaction between menin and MLL1 in steady-state or regenerative hematopoiesis and in B-cell differentiation despite the fact that MLL1 is critical for these processes. In B-cells, menin- or MLL1-regulated genes can be classified into three categories: 1) a relatively small group of co-regulated genes including previously described targets Hoxa9 and Meis1 but also Mecom and Eya1, and much larger groups of 2) exclusively menin-regulated and 3) exclusively MLL1-regulated genes. Our results highlight the large degree of independence of these two proteins and demonstrate that menin is not a requisite cofactor for MLL1 during normal hematopoiesis. Furthermore, our data support the development of menin-MLL1 disrupting drugs as safe and selective leukemia targeting agents. We performed gene expression analysis to determine the genes deregulated in B-cell progenitors upon loss of menin. Fraction B pro-B cells (defined as B220+CD43+HSA+BP-1- BM cells) were sorted from four MenF/F and four Rag1-cre;MenF/F mice of three weeks old. Total RNA was amplified once, labeled, fragmented and hybridized to Affymerix GeneChip Mouse Genome 430 2.0 array.
Project description:Global analysis of H3K4 methylation defines MLL family member targets and points to a role for MLL1-mediated H3K4 methylation in the regulation of transcriptional initiation by RNA polymerase II A common landmark of activated genes is the presence of trimethylation on lysine 4 of histone H3 (H3K4) at promoter regions. The Set1/COMPASS was the founding member and the only H3K4 methylases in S. cerevisiae, however, in mammals at least six H3K4 methylases Set1A/B and MLL1-4 are found in COMPASS-like complexes capable of methylating H3K4. To gain further insight into the different roles and functional targets for the H3K4 methylases, we have undertaken a genome-wide analysis of H3K4 methylation pattern in wild-type Mll1+/+ and Mll1-/- mouse fibroblasts (MEFs). We found that Mll1 is required for the H3K4 trimethylation of less than 5% of promoters carrying this modification. Many of these genes, which include developmental regulators such as Hox genes show decreased levels of RNA polymerase II recruitment and expression concomitant with the loss of H3K4 methylation. Although Mll1 is only required for the methylation of a subset of Hox genes, Menin, a component of the Mll1 and Mll2 complexes, is required for the overwhelming majority of H3K4 methylation at Hox loci. However, the loss of MLL3/4 and/or the Set1 complexes have little to no effect on the Hox loci H3K4 methylation or expression levels in these MEFs. Together these data provide insight into redundancy and specialization of COMPASS-like complexes in mammals and provide evidence on a possible role for Mll1-mediated H3K4 methylation in the regulation of transcriptional initiation. Chromatin Immunoprecipitation was performed with antibodies for histone 3 lysine 4 trimethylation, histone 3, and PolII in Mll1+/+ and Mll1-/- mouse embryonic fibroblasts. DNA was hybridized to a custom Agilent tiling array (4x44k format) that covers three of the hox regions (A,B,D) and a collection of other genes.
Project description:MLL1 and MLL2 profiling of OSCC cells following in vitro exposure to palmitic acid (PA) for 4 days and after 14 days of palmitic acid withdrawal.