Project description:Myocyte enhancer factor 2B (MEF2B) is a transcription factor with somatic mutation hotspots at K4, Y69 and D83 in diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL). The recurrence of these mutations indicates that they may drive lymphoma development. However, inferring the mechanisms by which they may drive lymphoma development was complicated by our limited understanding of MEF2B’s normal functions. To expand our understanding of the cellular activities of wildtype (WT) and mutant MEF2B, I developed and addressed two hypotheses: (1) identifying genes regulated by WT MEF2B will allow identification of cellular phenotypes affected by MEF2B activity and (2) contrasting the DNA binding sites, effects on gene expression and effects on cellular phenotypes of mutant and WT MEF2B will help refine hypotheses about how MEF2B mutations may contribute to lymphoma development. To address these hypotheses, I first identified genome-wide WT MEF2B binding sites and transcriptome-wide gene expression changes mediated by WT MEF2B. Using these data I identified and validated novel MEF2B target genes. I found that target genes of MEF2B included the cancer genes MYC, TGFB1, CARD11, NDRG1, RHOB, BCL2 and JUN. Identification of target genes led to findings that WT MEF2B promotes expression of mesenchymal markers, promotes HEK293A cell migration, and inhibits DLBCL cell chemotaxis. I then investigated how K4E, Y69H and D83V mutations change MEF2B’s activity. I found that K4E, Y69H and D83V mutations decreased MEF2B DNA binding and decreased MEF2B’s capacity to promote gene expression in both HEK293A and DLBCL cells. These mutations also reduced MEF2B’s capacity to alter HEK293A and DLBCL cell movement. From these data, I hypothesize that MEF2B mutations may promote DLBCL and FL development by reducing expression of MEF2B target genes that would otherwise function to help confine germinal centre B-cells to germinal centres. Overall, my research demonstrates how observations from genome-scale data can be used to identify cellular effects of candidate driver mutations. Moreover, my work provides a unique resource for exploring the role of MEF2B in cell biology: I map for the first time the MEF2B ‘regulome’, demonstrating connections between a relatively understudied transcription factor and genes significant to oncogenesis. ChIP-seq was performed using a V5 antibody on cells expressing V5 tagged WT and mutant MEF2B. Two biological replicates were performed on WT, K4E, Y69H and D83V MEF2B-V5 cells.
Project description:We report dynamics of X-chromosome upregulation (XCU) along X-chromosome inactivation (XCI) in mESCs as they differentiate into EpiSCs. F1 hybrid C57BL6/J × CAST/EiJ male and female mESCs were grown in serum/LIF conditions were differentiated using Fgf2 and Activin A for 1, 2, 4 and 7 days to induce random XCI in female cells. Multi-modal single-cell sequencing was performed using scATAC on nuclei and Smart-seq3 to assay chromatin accessibility and poly-A+ RNA expression, respectively. Allelic resolution is achieved using strain-specific SNPs in the data. We reveal dynamic balancing of X alleles as cells undergo XCI to compensate dosage imbalances between sexes as well as between X and autosomes. Furthermore, we reveal that female naïve mESCs with two active X chromosomes lack XCU on both alleles which has major implications for reprogramming studies. Finally, we estimate allelic transcriptional burst kinetics from the data and find that progressively increased burst frequencies underlies the XCU process.
Project description:We investigated SOX7 binding events on the chromatin under basal conditions in human umbilical vein endothelial cells, upon overexpression of human SOX7-mCherry and immunoprecipitating mCherry. Cells overexpressing only the mCherry tag were used as negative control condition, and peaks called here were substracted from the SOX7-mCherry peaks.
Project description:Transmission of genetic material from one generation to the next is a fundamental feature of all living cells. In eukaryotes, a macromolecular complex called the kinetochore plays crucial roles in this process by providing linkage between chromosomes and spindle microtubules. Little is known about this process in evolutionarily diverse protists. Within the supergroup Discoba, Eeuglenozoans forms a highly diversespeciose group of unicellular flagellates -including kinetoplastids, euglenids, and diplonemids. Kinetoplastids have an unconventional kinetochore system, while euglenids have a canonical onekinetochore system. It remains unclear what kind of kinetochores are present in diplonemids, a group of extremely diverse and abundant marine flagellatesplankton. Here, we employed deep homology detection protocols using profile-versus-profile Hidden Markov Model searches and AlphaFold-based structural comparisons to detect homologies that might have been previously missed. Interestingly, we still could not detect orthologs for most of the kinetoplastid nor canonical kinetochore subunits with few exceptions including a putative centromere-specific histone H3 variant (cenH3/CENP-A), the spindle checkpoint protein Mad2, the chromosomal passenger complex members Aurora and INCENP, and broadly conserved proteins like the CLK kinase and the meiotic synaptonemal complex proteins SYCP2 that function at kinetoplastid kinetochores. We examined the localization of five candidate kinetochore-associated proteins in the model diplonemid, Paradiplonema papillatum. PpCENP-A shows discrete dots in the nucleus, implying that it is likely a kinetochore component. PpMad2, PpCLK, PpSYCP2L1 and INCENP reside in the nucleus, but no clear kinetochore localization was observed. Altogether, these results raise a possibility that diplonemids evolved a hitherto unknown type of kinetochore system.
Project description:The human N-terminal acetyltransferase E (NatE) including its associated NatA co-translationally acetylates the N-terminus of about 40-60% of the proteome to mediate diverse biological processes including protein half-life, localization and protein interaction. In eukaryotes, the NatE complex contains the NAA50 catalytic subunit with substrate specificity for N-terminal methionine acetylation and NatA, which facilitates ribosomal targeting of the complex for co-translational activity. NatA, contains NAA10 catalytic and NAA15 auxiliary subunits, and forms a complex with a protein with intrinsic NAA10 inhibitory activity, HYPK. The molecular basis for how the human NAA10 and NAA50 catalytic subunits within NatE complex coordinate function and how HYPK regulates NatE activity is unknown. Here, we characterize the biochemical interplay between the human NAA10 and NAA50 catalytic subunits of NatE and its regulation by HYPK and correlate this to the cryo-EM structures of the human NatE and NatE/HYPK complexes. We show that NAA50 and HYPK exhibit negative cooperative binding to NatA in vitro and in human cells, by inducing NAA15 shifts in opposing directions. NAA50 and HYPK each contributes to NAA10 activity inhibition through structural alteration of the NAA10 substrate binding site. NatE is about 8-fold more active than NAA50, likely due to a reduced entropic cost for substrate binding through NatA tethering, but is inhibited by HYPK through structural alteration of the NatE substrate binding site. Taken together, these studies reveal the molecular basis for coordinated N-terminal acetylation by the NAA10 and NAA50 catalytic subunits of NatE and its modulation by HYPK.
Project description:We characterized the functions of the understudied LUC7-like family of splicing factors in human cells using seCLIP-seq, RBP knockdown followed by RNA-seq, and Co-IP mass spectrometry.
Project description:To test the differences in genome-wide DNA methylation signatures of haploid, diploid and triploid hESCs, we extracted genomic DNA from these cells and performed RRBS.
Project description:To search for factors regulating paternally imprinted genes (PEGs), we performed a genome-wide CRISPR/Cas9 screen in haploid hpESCs, and further analyzed the molecular phenotype upon perturbation of candidate PEGs regulators.