Project description:Meiotic chromosomes are highly compacted yet remain transcriptionally active. To understand how chromosome folding accommodates transcription, we investigated the assembly of the axial element, the proteinaceous structure that compacts meiotic chromosomes and promotes recombination and fertility. We found that the axial-element proteins of budding yeast are flexibly anchored to chromatin by the ring-like cohesin complex and biased towards small chromosomes by a separate modulating mechanism that requires the conserved axial element component Hop1. The ubiquitous presence of cohesin at sites of convergent transcription provides well-dispersed points for axis attachment and thus compaction. Axis protein enrichment at these sites directly correlates with the propensity for recombination initiation nearby. Importantly, axis anchoring by cohesin is adjustable and readily displaced in the direction of transcription by the transcriptional machinery. We propose that such robust but flexible tethering allows the highly structured axial element to promote recombination while easily adapting to changes in chromosome activity. ChIP-seq experiments were undertaken to understand the features of meiotic chromosomal axes assembly in meiosis. The genome-wide distribution of axis proteins including Hop1, Red1 as well as cohesin subunits Rec8 and Smc3 were measured. Axis protein binding pattern is also measured in rec8 mutant and pREC8-SCC1 in rec8 mutant.
Project description:Meiotic chromosomes are highly compacted yet remain transcriptionally active. To understand how chromosome folding accommodates transcription, we investigated the assembly of the axial element, the proteinaceous structure that compacts meiotic chromosomes and promotes recombination and fertility. We found that the axial element proteins of budding yeast are flexibly anchored to chromatin by the ring-like cohesin complex and biased towards small chromosomes by a separate modulating mechanism that requires the conserved axial-element component Hop1. The ubiquitous presence of cohesin at sites of convergent transcription provides well-dispersed points for axis attachment and thus compaction. Axis protein enrichment at these sites directly correlates with the propensity for recombination initiation. Importantly, axis anchoring by cohesin is adjustable and readily displaced in the direction of transcription by the transcriptional machinery. We propose that such robust but flexible tethering allows the axial element to promote recombination while easily adapting to changes in chromosome activity. 7 genome wide meiotic ChIP-seq sets: V5-Red1 DNA interaction (V5-Red1-ChIP), V5-Red1 DNA interaction in the absence of axis protein Hop1 (V5-Red1-ChIP, hop1delta), V5-Red1 DNA interaction in the absence of another two axis proteins Hop1 and Rec8 (V5-Red1-ChIP, hop1delta rec8delta), Rec8-HA DNA interaction (Rec8-HA-ChIP), Rec8-HA DNA interactionin the absence of Red1 (Rec8-HA-ChIP, red1delta), and 2 untagged control (V5-untagged-ChIP, HA-untagged-ChIP) (corresponding to the main Figure5)
Project description:Polycomb group (PcG) proteins are essential for accurate axial body patterning during embryonic development. PcG-mediated repression is conserved in metazoans and is targeted in Drosophila by Polycomb response elements (PREs). Targeting sequences in humans have not been described. While analyzing chromatin architecture in the context of human embryonic stem cell (hESC) differentiation, we discovered a 1.8kb region between HOXD11 and HOXD12 (D11.12) that is associated with PcG proteins, is nuclease hypersensitive, and shows alteration as hESCs differentiate. D11.12 repressed luciferase expression from a reporter construct both before and after differentiation of mesenchymal stem cells into adipocytes. Full repression by D11.12 required a highly conserved region and YY1 binding sites. Repression relied upon PcG proteins Bmi1 and Eed and a YY1-interacting partner, RYBP. We conclude that D11.12 is a Polycomb-dependent regulatory region with similarities to Drosophila PREs, indicating conservation in the mechanisms that target PcG function in mammals and flies. Data contains microarray measurements of the MNase-digested mononucleosomal fragments in hES cells, derived MSCs, osteoblasts and adipocytes. The ChIP-chip data includes Suz12, Bmi1 and H3K27me3 measurements in MSCs and adipocytes.
Project description:Vertebrate axial skeletal patterning is controlled by coordinated collinear expression of Hox genes and axial level-dependent activity of Hox protein combinations. Transcription factors of the Meis family act as cofactors of Hox proteins and profusely bind to Hox complex DNA, however their roles in mammalian axial patterning have not been established. Similarly, retinoic acid (RA) is known to regulate axial skeletal element identity through the transcriptional activity of its receptors, however whether this role is related to Meis/Hox regulation or functions in axial patterning remains unknown. Here we study the role of Meis factors in axial skeleton formation and its relationship to the RA pathway by characterizing Meis1, Meis2 and Raldh2 mutant mice. We report that Meis and Raldh2 regulate each other in a positive feedback regulatory loop that controls axial skeletal identity. Meis elimination produces homeotic transformations similar to those found in Raldh2 and anterior-Hox mutants and disrupts the expression of Hox target genes without changing the transcriptional profiles of Hox complexes. We propose that Meis regulates vertebrate axial skeleton patterning by exclusively affecting Hox protein function, and that alterations in RA levels can produce homeotic transformations without altering Hox transcription through regulating Meis expression.
Project description:Native ChIP on chip for H3K27me3 in murine ES cells comparing WT and Ring1B-/- cells. Paper Abstract: How polycomb group proteins repress gene expression in vivo is not known. Whilst histone modifying activities of the polycomb repressive complexes have been studied extensively, in vitro data has suggested a direct activity of the PRC1 complex in compacting chromatin. Here, we investigate higher-order chromatin compaction of polycomb targets in vivo. We show that polycomb repressive complexes are required to maintain a compact chromatin state at Hox loci in embryonic stem (ES) cells. There is specific decompaction in the absence of PRC2 or PRC1. This is due to PRC1, since decompaction occurs in Ring1B null cells that still have PRC2-mediated H3K27 methylation. Moreover, we show that the ability of Ring1B to restore a compact chromatin state, and to repress Hox gene expression in ES cells, is not dependent on its histone ubiquitination activity. We suggest that Ring1B-mediated chromatin compaction acts to directly limit transcription in vivo. Biological replicates: 3 independently grown, harvested,preplated, micrococcal nuclease digested and ChIP for H3K27me3. 5 Technical replicates.
Project description:ChIP on chip for H3K27me3 in murine ES cells comparing Undifferentiated and Day 3 differentiated. Paper Abstract: How polycomb group proteins repress gene expression in vivo is not known. Whilst histone modifying activities of the polycomb repressive complexes have been studied extensively, in vitro data has suggested a direct activity of the PRC1 complex in compacting chromatin. Here, we investigate higher-order chromatin compaction of polycomb targets in vivo. We show that polycomb repressive complexes are required to maintain a compact chromatin state at Hox loci in embryonic stem (ES) cells. There is specific decompaction in the absence of PRC2 or PRC1. This is due to PRC1, since decompaction occurs in Ring1B null cells that still have PRC2-mediated H3K27 methylation. Moreover, we show that the ability of Ring1B to restore a compact chromatin state, and to repress Hox gene expression in ES cells, is not dependent on its histone ubiquitination activity. We suggest that Ring1B-mediated chromatin compaction acts to directly limit transcription in vivo. Biological replicates: 3 independently grown, harvested, micrococcal nuclease digested and ChIP for H3K27me3. 6 Technical replicates.
Project description:Meiotic chromosomes are highly compacted yet remain transcriptionally active. To understand how chromosome folding accommodates transcription, we investigated the assembly of the axial element, the proteinaceous structure that compacts meiotic chromosomes and promotes recombination and fertility. We found that the axial element proteins of budding yeast are flexibly anchored to chromatin by the ring-like cohesin complex and biased towards small chromosomes by a separate modulating mechanism that requires the conserved axial-element component Hop1. The ubiquitous presence of cohesin at sites of convergent transcription provides well-dispersed points for axis attachment and thus compaction. Axis protein enrichment at these sites directly correlates with the propensity for recombination initiation. Importantly, axis anchoring by cohesin is adjustable and readily displaced in the direction of transcription by the transcriptional machinery. We propose that such robust but flexible tethering allows the axial element to promote recombination while easily adapting to changes in chromosome activity.