Unknown,Transcriptomics,Genomics,Proteomics

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Long range spreading of dosage compensation in Drosophila captures transcribed autosomal genes inserted on X

ABSTRACT: Dosage compensation in D. melanogaster males is achieved via targeting of the MSL complex to X chromosomal genes. This is proposed to involve initial sequence-specific recognition of the X at ~150-300 chromatin entry sites, and subsequent spreading to nearby active genes. Here we test a model in which the spreading step requires transcription and is sequence-independent. We ask whether, in the native context of the X chromosome, MSL complex will target genes of autosomal origin. We find that MSL complex does bind such genes, but only if transcriptionally active. Targeting is accompanied by acetylation of the histone H4K16 residue and two-fold transcriptional up-regulation. We conclude that the presence of a long-sought specific DNA sequence within X-linked genes is not obligatory for MSL complex binding. Instead, physical linkage and transcription play the pivotal roles in the identification of MSL targets irrespective of their origin and DNA sequence. Keywords: Epigenetics ChIP-seq measurements of MSL complex binding and input control. Chromatin was prepared from third instar male larvae of a genotype y w TrojanElephant; MSL3-TAP; msl3. TrojanElephant is a mini-white- and yellow-marked transposition of genomic region spanning 65 kb from cg13773 to snRNP70K. MSL3-TAP is a mini-white-marked TAP-tagged genomic msl3 transgene. IgG beads were used for pull-down.

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Peter Kharchenko

PROVIDER: E-GEOD-17729 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Active genes on the X chromosome of Drosophila males are upregulated by the Male-specific lethal (MSL) complex containing five MSL proteins and two non-coding roX RNAs. To probe the targeting mechanism, we have solved the structure of the MSL3 chromodomain, designed point mutations in key residues that disrupt putative methyl-lysine recognition, and tested their effect on full length MSL3 function. Transgenic males expressing these site-directed point mutants or MSL3short, a naturally occurring MSL3 form lacking the chromodomain, are unhealthy and developmentally delayed. Genomewide analyses of the binding patterns of these mutants support a two-step model: the first step is chromodomain-independent association with “chromatin entry sites” carrying GA-rich MSL recognition elements (MREs). The second step involves spreading from entry sites to the majority of active genes on the X. Either deleting or introducing point mutations in the MSL3 chromodomain disrupts this second step. In vitro studies demonstrate that chromodomain mutants have diminished interaction with recombinant nucleosomes methylated at H3K36. We propose that MSL spreading depends, to a large extent, on the integrity of the MSL3 chromodomain to interact with lysine-methylated nucleosomes. Chromatin immunoprecipitation using TAP-tag was performed as described previously (Alekseyenko et al., 2006). The immunoprecipitated material was eluted from the beads by adding 10 ?L (100 U) of AcTEV protease into 450 ?L of TEV buffer followed by incubation at 25°C for 1 h. To reverse the cross-links, samples were brought to 0.3M NaCl and 1% SDS and incubated at 65°C for 12 h. The samples were then extracted with phenol/chloroform/isoamyl alcohol followed by chloroform, and precipitated by ethanol in the presence of glycogen. The resulting precipitated DNA and the input DNA were amplified using a DNA linker as described (Strutt et al., 1997). LM-PCR (25 cycles) was performed using Platinum Pfu (Invitrogen). The resulting DNA was labeled and hybridized to arrays by NimbleGen Systems, Inc. Two-channel tiling arrays containing 388,000 probes were designed based on FlyBase 3.2. Chromosomes X and 19.6Mb of 2L were covered. The ChIP sample of interest was hybridized on one channel and genomic DNA was used as the reference on the other channel. Each ChIP-chip experiment was performed in duplicate.

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Long range spreading of dosage compensation in Drosophila captures transcribed autosomal genes inserted on X

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