Anne Corcoran
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• Recent, selected Publications
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Chromatin re-organisation regulates V(D)J recombination

B lymphocytes are cells of the immune system that produce antibodies (immunoglobulins) that recognize and inactivate foreign antigens such as bacteria. To cope with the enormous numbers of foreign antigens encountered in an individual's lifespan, these cells must produce millions of different antibodies. Recombination or ‘shuffling’ of genes in the immunoglobulin heavy chain (IgH) locus is the first step in generating this huge repertoire.

V(D)J recombination of the immunoglobulin heavy chain locus.
© Babraham Institute 2008 The IgH locus contains 200 variable (V) genes, 12 diversity (D) genes, and 4 joining (J) genes, which are recombined (cut and pasted) together in many different combinations; a D and a J gene are spliced together first, followed by a V gene (Figure 1).

Only one of each gene type is used in an individual cell, and the resulting DNA sequence codes for a unique IgH, which is expressed with an Ig light chain as a unique highly specific antibody in each cell.


Our aim is to understand the chromatin remodelling mechanisms that open up the IgH locus in B cells to enable V(D)J recombination. Its chromatin structure (DNA wrapped around nucleosomes composed of histone proteins) is highly compacted and inaccessible in non-B cells. It must be unfolded to give access to the enzymes RAG1 and RAG2 that catalyse the DNA breaks (cutting) of VDJ rearrangement. If the locus isn't opened up enough, too few antibodies are made, resulting in immunodeficiency. Conversely if it’s opened up excessively, or not closed down after recombination, inappropriate DNA breaks may occur, which may be repaired incorrectly causing B cell lymphomas.

RNA fluorescence in situ hybridisation analysis of antisense intergenic transcription. Nuclei from β lymphocytes undergoing V to DJ recombination are stained in blue. Antisense transcripts are detected by green fluorescence. Note the extended pattern compared to the control probe (red) that marks one active IgH gene.
© Babraham Institute 2008 We are particularly interested in the role of non-coding RNA in this process. Large-scale sequence analysis has revealed that the majority of RNAs in the genome are non-coding ie do not produce protein. Further, 20% of RNAs come from the non-coding strand (antisense transcripts). There is intense interest in the function of these transcripts. They may regulate activation of large chromatin domains that are differentially expressed in different cell lineages, as shown for the b-globin locus. We and others have previously shown that non-coding RNA transcripts are generated from individual V genes prior to recombination, although it is still unknown if they play a directive role.

Recently we have shown that antisense transcription, both genic and intergenic (between genes) occurs throughout the V region prior to V to DJ recombination. It is then switched off after recombination. The transcripts appear large and may cover several genes. Our work suggests that this transcription process drives through the entire large closed V region and opens up the chromatin into a poised state to facilitate further remodelling and recombination at the V genes. It may then be downregulated to prevent inappropriate recombination.

Antisense transcription opens up the IgH locus to enable V to DJ recombination. Large arrows - antisense intergenic transcription. Small arrows - sense transcription over V genes.
© Babraham Institute 2008 This is the first example of antisense transcription that is not associated with transcriptional repression, and suggests antisense intergenic transcription may remodel closed chromatin to regulate recombination of other antigen receptor loci and transcription of other large multigene developmentally regulated loci. We are currently investigating how widespread this process is and how it is regulated.


Recent, selected publications

Bolland D, Corcoran AE (2007) Somatic hypermutation is a matter of choice.
Nature Immunology 8 677-679
http://dx.doi.org/10.1038/ni0707-677

Bolland DJ, Wood AL, Afshar R, Featherstone K, Oltz EM, Corcoran AE (2007) Antisense intergenic transcription precedes Igh D-to-J recombination and is controlled by the intronic enhancer, Eμ
Molecular and Cellular Biology 27 5523-5533
http://dx.doi.org/10.1128/MCB.02407-06

Osborne CS, Chakalova L, Mitchell JA, Horton AM, Wood AL, Bolland DJ, Corcoran AE, Fraser P (2007) Myc dynamically and preferentially relocates to a transcription factory occupied by Igh.
PLoS Biology 5 e192, 1763-1772
http://dx.doi.org/10.1371/journal.pbio.0050192

Afshar R, Pierce S, Bolland DJ, Corcoran AE, Oltz EM (2006) Regulation of IgH gene assembly: role of the intronic enhancer and 5'DQ52 region in targeting DHJH recombination.
Journal of Immunology 176 2439-2447
http://www.jimmunol.org/cgi/content/abstract/176/4/2439

Johnston CM, Wood AL, Bolland DJ, Corcoran AE (2006) Complete sequence assembly and characterization of the C57BL/6 mouse Ig heavy chain V region.
Journal of Immunology 176 4221-4234
http://www.jimmunol.org/cgi/content/abstract/176/7/4221

Corcoran AE (2005) Immunoglobulin locus silencing and allelic exclusion.
Seminars in Immunology 17 141-154
http://dx.doi.org/10.1016/j.smim.2005.01.002

Erlandsson L, Licence ST, Gaspal F, Lane P, Corcoran AE, Martensson I-L (2005) Both the pre-BCR and the IL-7Rα are essential for expansion at the pre-BII cell stage in vivo.
European Journal of Immunology 35 1969-1976
http://dx.doi.org/10.1002/eji.200425821

Bolland DJ, Wood AL, Johnston CM, Bunting SF, Morgan G, Chakalova L, Fraser P, Corcoran AE (2004) Antisense intergenic transcription in V(D)J recombination.
Nature Immunology 5 630-637
http://dx.doi.org/10.1038/ni1068

Erlandsson L, Licence ST, Gaspal F, Bell S, Lane P, Corcoran AE, Martensson I-L (2004) Impaired B-1 and B-2 B cell development and atypical splenic B cell structures in IL-7 receptor-deficient mice.
European Journal of Immunology 34 3595-3603
http://dx.doi.org/10.1002/eji.200425217

The Corcoran Group
© Babraham Institute 2008 Group Members

Daniel Bolland - Postdoc
Adam Bowen - Postdoc

Louise Matheson - PhD Student
Andrew Wood - PhD Student
Varsha Jagadesham - PhD Student