Unknown,Transcriptomics,Genomics,Proteomics

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Genome-wide analysis of condensin binding sites in vertebrate genome

ABSTRACT: The condensin complex is well known to be essential for correct packaging and segregation of chromosomes during mitosis and meiosis in all eukaryotes. To date, the genome wide location and the nature of condensin binding sites has remained elusive in vertebrate systems. A detailed knowledge of condensin binding sites is essential to understand the as-yet enigmatic function of this complex and to define its greater role in chromosome architecture. To address this, we have used next generation sequencing to map condensin I in chicken DT40 cells. Unexpectedly, we found condensin I binds predominately to promoter sequences in mitotic cells. We also found a striking enrichment at both centromeres and telomeres, highlighting the importance of the complex in chromosome segregation. Taken together, the results show condensin I is largely absent from heterochromatic regions. These results reveal for the first time the condensin I binding sites in the vertebrate genome, and demonstrate the importance of the complex in genome segregation and suggest a novel function in gene regulation. Condensin associated DNA from chicken DT40 cells were affinity purified using streptavidin and deep sequenced by Illumina Hiseq2000

ORGANISM(S): Gallus gallus

SUBMITTER: Ji Hun Kim

PROVIDER: E-GEOD-45552 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID. Sequencing of the IgL V region and mutationally active GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells for evidence of AID dependent mutations. ChIP-seq proiles of RNA Pol II, Spt5, and pSer5 Pol II at a GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells.

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Genome-wide analysis of condensin binding sites in vertebrate genome

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