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Regulation of B cell fate commitment and immunoglobulin heavy-chain gene rearrangements by Ikaros

Abstract

The transcription factor Ikaros is essential for B cell development. However, its molecular functions in B cell fate specification and commitment have remained elusive. We show here that the transcription factor EBF restored the generation of CD19+ pro–B cells from Ikaros-deficient hematopoietic progenitors. Notably, these pro–B cells, despite having normal expression of the transcription factors EBF and Pax5, were not committed to the B cell fate. They also failed to recombine variable gene segments at the immunoglobulin heavy-chain locus. Ikaros promoted heavy-chain gene rearrangements by inducing expression of the recombination-activating genes as well as by controlling accessibility of the variable gene segments and compaction of the immunoglobulin heavy-chain locus. Thus, Ikaros is an obligate component of a network that regulates B cell fate commitment and immunoglobulin heavy-chain gene recombination.

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Figure 1: EBF expression restores the development of B cells from Ikzf1−/− hematopoietic progenitors.
Figure 2: Ikzf1−/− pro–B cells can trans-differentiate into macrophages.
Figure 3: Restoration of Ik-1 expression in Ikzf1−/− pro–B cells promotes B lineage commitment.
Figure 4: Restoration of Ik-1 expression in Ikzf1−/− pro–B cells induces Rag expression and VH-to-DJH rearrangements.
Figure 5: Ikaros binds to the Rag locus and regulates histone acetylation.
Figure 6: Ikaros regulates the accessibility of VH distal segments.
Figure 7: Ikaros is required for compaction of the Igh locus.

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Acknowledgements

We thank members of the Singh lab for suggestions and comments. Plasmids pEBB-Rag1 and pEBB-Rag2 were gifts from D.G. Schatz (Yale University); Pax5−/− pro–B cells were a gift from M. Busslinger (Research Institute of Molecular Pathology). Supported by the Irvington Institute Fellowship program of the Cancer Research Institute (I.A.D.), the Research Council of Norway (H.Sc.), the China Scholarship Council (Z.C.), the National Institutes of Health (R01 DK43726 to S.T.S.) and the Howard Hughes Medical Institute (H.Si.).

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D.R. designed and did the experiments, analyzed data and wrote the manuscript; I.A.D. and K.L.R. contributed immuno-FISH data; H.Sc. did EMSA; Z.C. helped with RT-PCR analysis; E.B., S.T.S. and S.W. provided experimental advice; and H.Si. supervised the research and wrote the manuscript.

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Correspondence to Harinder Singh.

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Reynaud, D., A Demarco, I., L Reddy, K. et al. Regulation of B cell fate commitment and immunoglobulin heavy-chain gene rearrangements by Ikaros. Nat Immunol 9, 927–936 (2008). https://doi.org/10.1038/ni.1626

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