Functions of E2A-HEB Heterodimers in T-Cell Development Revealed by a Dominant Negative Mutation of HEB

Abstract

Lymphocyte development and differentiation are regulated by the basic helix-loop-helix (bHLH) transcription factors encoded by the E2A and HEB genes. These bHLH proteins bind to E-box enhancers in the form of homodimers or heterodimers and, consequently, activate transcription of the target genes. E2A homodimers are the predominant bHLH proteins present in B-lineage cells and are shown genetically to play critical roles in B-cell development. E2A-HEB heterodimers, the major bHLH dimers found in thymocyte extracts, are thought to play a similar role in T-cell development. However, disruption of either the E2A or HEBgene led to only partial blocks in T-cell development. The exact role of E2A-HEB heterodimers and possibly the E2A and HEB homodimers in T-cell development cannot be distinguished in simple disruption analysis due to a functional compensation from the residual bHLH homodimers. To further define the function of E2A-HEB heterodimers, we generated and analyzed a dominant negative allele of HEB, which produces a physiological amount of HEB proteins capable of forming nonfunctional heterodimers with E2A proteins. Mice carrying this mutation show a stronger and earlier block in T-cell development than HEB complete knockout mice. The developmental block is specific to the α/β T-cell lineage at a stage before the completion of V(D)J recombination at the TCRβ gene locus. This defect is intrinsic to the T-cell lineage and cannot be rescued by expression of a functional T-cell receptor transgene. These results indicate that E2A-HEB heterodimers play obligatory roles both before and after TCRβ gene rearrangement during the α/β lineage T-cell development.

ACKNOWLEDGMENTS

We thank Jenifer Hanrahan and Reshma Rangwala for assistance in making constructs, Mike Cook for assistance in flow cytometry analysis, and Lihua Pan, Jenifer Hanrahan, Steve Greenbaum, Curtis Bradney, and Michael Krangel for critical reading of the manuscript.

This work has been supported by the Leukemia Society of America Scholarship, the Whitehead Scholarship, and NIH grants (R01CA72433 and R01GM59638) to Y.Z.