The E2A gene products, E12 and E47, are critical for proper early B-cell development and commitment to the B-cell lineage. Here we reveal a new role for E2A in T-lymphocyte development. Loss of E2A activity results in a partial block at the earliest stage of T-lineage development. This early T-cell phenotype precedes the development of a T-cell lymphoma which occurs between 3 and 9 months of age. The thymomas are monoclonal and highly malignant and display a cell surface phenotype similar to that of immature thymocytes. In addition, the thymomas generally express high levels of c-myc. As assayed by comparative genomic hybridization, each of the tumor populations analyzed showed a nonrandom gain of chromosome 15, which contains the c-myc gene. Taken together, the data suggest that the E2A gene products play a role early in thymocyte development that is similar to their function in B-lineage determination. Furthermore, the lack of E2A results in development of T-cell malignancies, and we propose that E2A inactivation is a common feature of a wide variety of human T-cell proliferative disorders, including those involving the E2A heterodimeric partners tal-1 and lyl-1.The E2A gene encodes two basic helix-loop-helix (HLH) transcription factors, E12 and E47 (32). E12 and E47, members of the class I HLH proteins, are characterized by their broad expression pattern and their ability to bind DNA either as homodimers or as heterodimers with tissue-specific HLH proteins (9,22,33,40,43). Class I HLH proteins share several highly conserved domains. The HLH domain mediates homoand/or heterodimerization, and the basic region constitutes the sequence-specific DNA binding domain (11,22,32,50). In addition, two distinct domains located in the N-terminal portion of the class I HLH proteins have been shown to be required for transactivation (1,26,39).E12 and E47 arise through differential splicing to the exon that encodes for the HLH domain. Within the HLH domain, their amino acid sequences differ by 20% (32). Both E12 and E47 have the ability to form heterodimers with class II HLH members, including the myogenic regulators (9, 23). However, E12 and E47 have distinct biochemical properties. E47 homodimers bind with high affinity to DNA, whereas an inhibitory domain present in E12 prevents those homodimers from high-affinity DNA binding (46).E2A polypeptides bind to E-box sites present in a wide variety of tissue-specific enhancers, including the insulin, muscle creatine kinase, and immunoglobulin (Ig) intronic and 3Ј enhancers (16,22,28,32,35,38,52). In B cells, it is homodimers of the E2A gene products that bind to E2-box sites present in the Ig enhancers (2,34,43). That E2A gene products play a crucial role in B lymphocyte development has been demonstrated recently by the generation of E2A-deficient mice and transgenic mice overexpressing Id1, an inhibitor of E2A (3,47,56). In the absence of E2A activity, even the earliest committed B-cell precursors are undetectable in the bone marrow (3,47,56). In addition, E2A-deficient mice l...

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Natural killer T cells (NKT cells) have stimulatory or inhibitory effects on the immune response that can be attributed in part to the existence of functional subsets of NKT cells. These subsets have been characterized only on the basis of the differential expression of a few transcription factors and cell-surface molecules. Here we have analyzed purified populations of thymic NKT cell subsets at both the transcriptomic level and epigenomic level and by single-cell RNA sequencing. Our data indicated that despite their similar antigen specificity, the functional NKT cell subsets were highly divergent populations with many gene-expression and epigenetic differences. Therefore, the thymus ‘imprints’ distinct gene programs on subsets of innate-like NKT cells that probably impart differences in proliferative capacity, homing, and effector functions.

The E2A gene encodes the E47 and E12 basic helix-loop-helix (bHLH) transcription factors. T cell development in E2A-deficient mice is partially arrested before lineage commitment. Here we demonstrate that E47 expression becomes uniformly high at the point at which thymocytes begin to commit towards the T cell lineage. E47 protein levels remain high until the double positive developmental stage, at which point they drop to relatively moderate levels, and are further downregulated upon transition to the single positive stage. However, stimuli that mimic pre-T cell receptor (TCR) signaling in committed T cell precursors inhibit E47 DNA-binding activity and induce the bHLH inhibitor Id3 through a mitogen-activated protein kinase kinase–dependent pathway. Consistent with these observations, a deficiency in E2A proteins completely abrogates the developmental block observed in mice with defects in TCR rearrangement. Thus E2A proteins are necessary for both initiating T cell differentiation and inhibiting development in the absence of pre-TCR expression. Mechanistically, these data link pre-TCR mediated signaling and E2A downstream target genes into a common pathway.

Helix-loop-helix proteins are essential factors for lymphocyte development and function. In particular, E-proteins are crucial for commitment of lymphoid progenitors to the B- and T-cell lineages. E-proteins are negatively regulated by the Id class of helix-loop-helix proteins. The Id proteins function as dominant-negative inhibitors of E-proteins by inhibiting their ability to bind DNA. Here, we review the role of E-proteins and their Id protein antagonists in lymphocyte proliferation and developmental progression. In addition, we discuss how E-protein activity and Id gene expression are regulated by T-cell receptor (TCR) and pre-TCR-mediated signalling.