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The MSL3 chromodomain directs a key targeting step for dosage compensation of the Drosophila melanogaster X chromosome.

Sural TH, Peng S, Li B, Workman JL, Park PJ, Kuroda MI - Nat. Struct. Mol. Biol. (2008)

Bottom Line: Using ChIP-chip analysis, we find that MSL3 chromodomain mutants retain binding to chromatin entry sites but show a clear disruption in the full pattern of MSL targeting in vivo, consistent with a loss of spreading.Furthermore, when compared to wild type, chromodomain mutants lack preferential affinity for nucleosomes containing H3K36me3 in vitro.Our results support a model in which activating complexes, similarly to their silencing counterparts, use the nucleosomal binding specificity of their respective chromodomains to spread from initiation sites to flanking chromatin.

View Article: PubMed Central - PubMed

Affiliation: Harvard-Partners Center for Genetics and Genomics, Division of Genetics, Department of Medicine, Brigham & Women's Hospital, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115, USA.

ABSTRACT
The male-specific lethal (MSL) complex upregulates the single male X chromosome to achieve dosage compensation in Drosophila melanogaster. We have proposed that MSL recognition of specific entry sites on the X is followed by local targeting of active genes marked by histone H3 trimethylation (H3K36me3). Here we analyze the role of the MSL3 chromodomain in the second targeting step. Using ChIP-chip analysis, we find that MSL3 chromodomain mutants retain binding to chromatin entry sites but show a clear disruption in the full pattern of MSL targeting in vivo, consistent with a loss of spreading. Furthermore, when compared to wild type, chromodomain mutants lack preferential affinity for nucleosomes containing H3K36me3 in vitro. Our results support a model in which activating complexes, similarly to their silencing counterparts, use the nucleosomal binding specificity of their respective chromodomains to spread from initiation sites to flanking chromatin.

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A model for MSL3 chromodomain-dependent spreading(a) An initial group of sequence-dependent targets recruit the complex and lead to upregulation of transcription via local acetylation, which is sufficient for marginal survival. A second class of genes is targeted by spreading mediated by the MSL3 chromodomain, partly via the recognition of H3K36Me mark at 3’ ends of active genes. (b) In the chromodomain mutants, targeting by spreading is defective. The complex is not stabilized at 3’ ends of targets and diffuses away.
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Figure 6: A model for MSL3 chromodomain-dependent spreading(a) An initial group of sequence-dependent targets recruit the complex and lead to upregulation of transcription via local acetylation, which is sufficient for marginal survival. A second class of genes is targeted by spreading mediated by the MSL3 chromodomain, partly via the recognition of H3K36Me mark at 3’ ends of active genes. (b) In the chromodomain mutants, targeting by spreading is defective. The complex is not stabilized at 3’ ends of targets and diffuses away.

Mentions: The data presented here are summarized in a two-step model for targeting of the MSL complex to the X chromosome (Fig. 6). In this model, there are 2 classes of MSL target genes on the X, sequence-dependent chromatin entry sites and chromodomain-dependent active genes. Initially, MSL complex recognizes specific MREs within entry sites on the X chromosome, leading to local acetylation of nearby targets27,35. The local acetylation at these sites is sufficient for marginal survival and this step is independent of the MSL3 chromodomain. In a second step, the MSL3 chromodomain directs the complex to more distant genes by recognizing H3K36 methylated nucleosomes (Fig. 6a), probably in conjunction with general DNA and nucleosomal binding21,25. Whether MSL complex actually traverses intergenic regions or releases and reattaches to nearby active genes is not known. Furthermore, chromodomain defects may lead to secondary effects on spreading through other MSL subunits, although our nucleosomal binding analysis using recombinant MSL3 protein strongly suggests a direct effect. Regardless, in the absence of the MSL3 chromodomain, the spreading step is defective (Fig. 6b). How far the complex will travel without the chromodomain may depend on the local MSL concentration at the nearest chromatin entry site.


The MSL3 chromodomain directs a key targeting step for dosage compensation of the Drosophila melanogaster X chromosome.

Sural TH, Peng S, Li B, Workman JL, Park PJ, Kuroda MI - Nat. Struct. Mol. Biol. (2008)

A model for MSL3 chromodomain-dependent spreading(a) An initial group of sequence-dependent targets recruit the complex and lead to upregulation of transcription via local acetylation, which is sufficient for marginal survival. A second class of genes is targeted by spreading mediated by the MSL3 chromodomain, partly via the recognition of H3K36Me mark at 3’ ends of active genes. (b) In the chromodomain mutants, targeting by spreading is defective. The complex is not stabilized at 3’ ends of targets and diffuses away.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
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Figure 6: A model for MSL3 chromodomain-dependent spreading(a) An initial group of sequence-dependent targets recruit the complex and lead to upregulation of transcription via local acetylation, which is sufficient for marginal survival. A second class of genes is targeted by spreading mediated by the MSL3 chromodomain, partly via the recognition of H3K36Me mark at 3’ ends of active genes. (b) In the chromodomain mutants, targeting by spreading is defective. The complex is not stabilized at 3’ ends of targets and diffuses away.
Mentions: The data presented here are summarized in a two-step model for targeting of the MSL complex to the X chromosome (Fig. 6). In this model, there are 2 classes of MSL target genes on the X, sequence-dependent chromatin entry sites and chromodomain-dependent active genes. Initially, MSL complex recognizes specific MREs within entry sites on the X chromosome, leading to local acetylation of nearby targets27,35. The local acetylation at these sites is sufficient for marginal survival and this step is independent of the MSL3 chromodomain. In a second step, the MSL3 chromodomain directs the complex to more distant genes by recognizing H3K36 methylated nucleosomes (Fig. 6a), probably in conjunction with general DNA and nucleosomal binding21,25. Whether MSL complex actually traverses intergenic regions or releases and reattaches to nearby active genes is not known. Furthermore, chromodomain defects may lead to secondary effects on spreading through other MSL subunits, although our nucleosomal binding analysis using recombinant MSL3 protein strongly suggests a direct effect. Regardless, in the absence of the MSL3 chromodomain, the spreading step is defective (Fig. 6b). How far the complex will travel without the chromodomain may depend on the local MSL concentration at the nearest chromatin entry site.

Bottom Line: Using ChIP-chip analysis, we find that MSL3 chromodomain mutants retain binding to chromatin entry sites but show a clear disruption in the full pattern of MSL targeting in vivo, consistent with a loss of spreading.Furthermore, when compared to wild type, chromodomain mutants lack preferential affinity for nucleosomes containing H3K36me3 in vitro.Our results support a model in which activating complexes, similarly to their silencing counterparts, use the nucleosomal binding specificity of their respective chromodomains to spread from initiation sites to flanking chromatin.

View Article: PubMed Central - PubMed

Affiliation: Harvard-Partners Center for Genetics and Genomics, Division of Genetics, Department of Medicine, Brigham & Women's Hospital, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115, USA.

ABSTRACT
The male-specific lethal (MSL) complex upregulates the single male X chromosome to achieve dosage compensation in Drosophila melanogaster. We have proposed that MSL recognition of specific entry sites on the X is followed by local targeting of active genes marked by histone H3 trimethylation (H3K36me3). Here we analyze the role of the MSL3 chromodomain in the second targeting step. Using ChIP-chip analysis, we find that MSL3 chromodomain mutants retain binding to chromatin entry sites but show a clear disruption in the full pattern of MSL targeting in vivo, consistent with a loss of spreading. Furthermore, when compared to wild type, chromodomain mutants lack preferential affinity for nucleosomes containing H3K36me3 in vitro. Our results support a model in which activating complexes, similarly to their silencing counterparts, use the nucleosomal binding specificity of their respective chromodomains to spread from initiation sites to flanking chromatin.

Show MeSH