Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Transcription profiling of C. elegans to investigate dosage compensation complex (DCC) binding and function

ABSTRACT: In many species, a dosage compensation complex (DCC) is targeted to X chromosomes of one sex to equalize levels of X gene products between males (1X) and females (2X). Here we identify cis-acting regulatory elements that target the C. elegans X chromosome for repression by the DCC. The DCC binds to discrete, dispersed sites on X of two types. rex sites recruit the DCC in an autonomous, DNA sequence-dependent manner using a 12 bp consensus motif that is enriched on X. This motif is critical for DCC binding, is clustered in rex sites, and confers much of X-chromosome specificity. Motif variants enriched on X by 3.8-fold or more are highly predictive (95%) for rex sites. In contrast, dox sites lack the X-enriched variants and cannot bind the DCC when detached from X. dox sites are more prevalent than rex sites and, unlike rex sites, reside preferentially in promoters of some expressed genes. These findings fulfill predictions for a targeting model in which the DCC binds to recruitment sites on X and disperses to discrete sites lacking autonomous recruitment ability. To relate DCC binding to function, we identified dosage-compensated and non-compensated genes on X. Unexpectedly, many genes of both types have bound DCC, but many do not, suggesting the DCC acts over long distances to repress X gene expression. Remarkably, the DCC binds to autosomes, but at far fewer sites and rarely at consensus motifs. DCC disruption causes opposite effects on expression of X and autosomal genes. The DCC thus acts at a distance to impact expression throughout the genome. Experiment Overall Design: For microarray analysis, the nematode strains and number of experiments was as follows: TY2222, her-1(hv1y101); xol-1(y9) sdc-2(y74) unc-9(e101), XO embryos (8 biological replicas and 6 wild-type XX embryos controls ), dpy-27(y57) XX embryos (3 biological replicas and 3 wild-type XX embryos controls), and sdc-2(y93, RNAi) XX embryos (3 biological replicas and 3 wild-type XX embryos controls).

ORGANISM(S): Caenorhabditis elegans

SUBMITTER: Barbara Meyer

PROVIDER: E-GEOD-14649 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Here we exploit the essential process of X-chromosome dosage compensation to elucidate basic mechanisms that control the assembly, genome-wide binding, and function of gene regulatory complexes that act over large chromosomal territories. We demonstrate that a subunit of C. elegans MLL/COMPASS, a gene-activation complex, acts within the dosage compensation complex (DCC), a condensin complex, to target the DCC to both X chromosomes of hermaphrodites and thereby reduce chromosome-wide gene expression. The DCC binds to two categories of sites on X: rex sites that recruit the DCC in an autonomous, sequence- dependent manner, and dox sites that reside primarily in promoters of expressed genes and bind the DCC robustly only when attached to X. We find that DCC mutants that abolish rex-site binding do not eliminate dox-site binding, but instead reduce it to the level observed at autosomal binding sites in wild-type animals. Changes in DCC binding to these non-rex sites occur throughout development and correlate with transcriptional activity of adjacent genes. Moreover, autosomal DCC binding is enhanced by rex-site binding in cis in X-autosome fusion chromosomes. Thus, dox and autosomal sites exhibit similar binding properties. Our data support a model for DCC binding in which low-level DCC binding at dox and autosomal sites is dictated by intrinsic properties correlated with high transcriptional activity. Sex-specific DCC recruitment to rex sites then greatly elevates DCC binding to dox sites in cis, which lack intrinsically high DCC affinity on their own. We also show here that the C. elegans DCC achieves dosage compensation through its effects on transcription. ChIP-chip experiments using antibodies against DPY-27, SDC-3, DPY-30, DPY-26, MIX-1, SMC-4, ASH-2 in wild-type embryos. ChIP-chip experiments using antibodies against SDC-3, DPY-27, DPY-30, ASH-2, and IgG in different DCC mutants. ChIP-chip experiments using antibodies against RNA Pol II (hypophosphorylated and S2 and S5) in wild type and sdc-2 partial loss of function mutants.

Project description:The essential process of dosage compensation equalizes X-chromosome gene expression between C. elegans XO males and XX hermaphrodites through a dosage compensation complex (DCC) that resembles condensin. The DCC binds to both X chromosomes of hermaphrodites to repress transcription by half. Here we show that post-translational modification by the SUMO conjugation pathway is essential for sex-specific assembly of the DCC onto X. Depletion of the SUMO peptide in vivo severely disrupts binding of particular DCC subunits and causes changes in X-linked gene expression similar to those caused by disrupting genes encoding DCC subunits. Three DCC subunits are themselves SUMOylated, and depletion of SUMO preferentially reduces their binding to X, suggesting that SUMOylation of DCC subunits is essential for robust association with X. DCC SUMOylation is triggered by the signal that initiates DCC assembly onto X. The initial step of assembly--binding of X-targeting factors to recruitment sites on X (rex sites)--is independent of SUMOylation, but robust binding of the complete complex requires SUMOylation. SUMOylated DCC subunits are enriched at rex sites, and SUMOylation enhances interactions between X-targeting factors and condensin subunits that facilitate DCC binding beyond the low level achieved without SUMOylation. DCC subunits also participate in condensin complexes essential for chromosome segregation, but their SUMOylation occurs only in the context of the DCC. Our results reinforce a newly emerging theme in which multiple proteins of a complex are SUMOylated in response to a specific stimulus, leading to accelerated complex formation and enhanced function. ChIP-chip experiments using antibodies against DPY-27, SDC-3, DPY-30, DPY-26, DPY-28 and FLAG-tagged SDC-2 in wild-type and smo-1 RNAi treated mixed embryos, with IGG controls. Also, sequential ChIP-chip experiments: (1) ChIP using FLAG antibodies to determine the genome-wide binding sites for SUMOylated proteins, (2) ChIP using FLAG antibodies followed by re-ChIP of eluted protein-chromatin complexes with DPY-27 antibodies to determine genome-wide binding sites for SUMOylated DPY-27 (referred to as DPY-27 re-ChIP experiments), (3) ChIP using FLAG antibodies followed by re-ChIP of eluted protein-chromatin with IGG antibodies to determine background binding (referred to as IGG re-ChIP experiments, and (4) ChIP using DPY-27 antibodies as a control to assess the efficiency of DPY-27 binding and detection in control vs. FLAG-tagged strains.

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Transcription profiling of C. elegans to investigate dosage compensation complex (DCC) binding and function

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