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Induction of the early growth response (Egr) family of transcription factors during thymic selection.

Shao H, Kono DH, Chen LY, Rubin EM, Kaye J - J. Exp. Med. (1997)

Bottom Line: A similar pattern of expression is found for family members Egr-2 and Egr-3.In contrast, the calcineurin inhibitor cyclosporin A, which inhibits DPK cell differentiation as well as positive selection, inhibits expression of Egr-2 and Egr-3, but not Egr-1.The identification of the Egr family in this context represents the first report of a link between the two known signaling pathways involved in positive selection and downstream transcriptional regulators.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, The Scripps Research Institute, La Jolla, California 92037, USA.

ABSTRACT
There is little known about the regulation of gene expression during TCR-mediated differentiation of immature CD4+8+ (double positive) thymocytes into mature T cells. Using the DPK CD4+8+ thymocyte precursor cell line, we demonstrate that the early growth response-1 gene (Erg-1), encoding a zinc finger transcription factor, is rapidly upregulated after TCR stimulation. We also report that Egr-1 is expressed by a subset of normal double positive thymocytes in the thymic cortex, as well by a majority of medullary single positive thymocytes. Expression of Egr-1 is dramatically reduced in the thymus of major histocompatibility complex knockout mice, but can be induced by anti-CD3 antibody stimulation of isolated thymocytes from these animals. These and other data suggest that high level expression of Egr-1 in the thymus is a consequence of selection. A similar pattern of expression is found for family members Egr-2 and Egr-3. Using the DPK cell line, we also demonstrate that expression of Egr-1, 2, and 3 is dependent upon ras activation, as is the initiation of differentiation to a single positive cell. In contrast, the calcineurin inhibitor cyclosporin A, which inhibits DPK cell differentiation as well as positive selection, inhibits expression of Egr-2 and Egr-3, but not Egr-1. The identification of the Egr family in this context represents the first report of a link between the two known signaling pathways involved in positive selection and downstream transcriptional regulators.

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Expression of Egr-1 protein in the thymus. Thin sections of normal thymus (A–C) or MHC knockout thymus (D) were fixed in formaldehyde and stained with a specific rabbit anti-Egr-1 peptide antiserum (A, C, D) or the same antibody preincubated with specific peptide (B). Regions of  cortex (C) and medulla (M) are indicated. Sections were counterstained with hematoxylin and photographed at ×20 (A, B) or ×40 (C, D). C shows a  magnification of the same section photographed in A.
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Figure 8: Expression of Egr-1 protein in the thymus. Thin sections of normal thymus (A–C) or MHC knockout thymus (D) were fixed in formaldehyde and stained with a specific rabbit anti-Egr-1 peptide antiserum (A, C, D) or the same antibody preincubated with specific peptide (B). Regions of cortex (C) and medulla (M) are indicated. Sections were counterstained with hematoxylin and photographed at ×20 (A, B) or ×40 (C, D). C shows a magnification of the same section photographed in A.

Mentions: To determine the location of cells within the thymus that express Egr-1 protein, thin sections of normal thymus were stained with a specific anti–Egr-1 peptide antiserum (Fig. 8). Isolated cells scattered throughout the cortex were found to express Egr-1. No enrichment of Egr-1 expressing cells in the subcapsular region or cortico-medullary junction was observed. These results are consistent with induction of Egr-1 in cortical double positive thymocytes as a result of TCR engagement. Most, but not all, medullary cells also stained, indicating that Egr-1 protein is expressed in a substantial number of single positive thymocytes as well (see below). In contrast, few cells stained in the thymic cortex of MHC-deficient mice, and in general the staining was weak, even in medullary regions (Fig. 8).


Induction of the early growth response (Egr) family of transcription factors during thymic selection.

Shao H, Kono DH, Chen LY, Rubin EM, Kaye J - J. Exp. Med. (1997)

Expression of Egr-1 protein in the thymus. Thin sections of normal thymus (A–C) or MHC knockout thymus (D) were fixed in formaldehyde and stained with a specific rabbit anti-Egr-1 peptide antiserum (A, C, D) or the same antibody preincubated with specific peptide (B). Regions of  cortex (C) and medulla (M) are indicated. Sections were counterstained with hematoxylin and photographed at ×20 (A, B) or ×40 (C, D). C shows a  magnification of the same section photographed in A.
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Related In: Results  -  Collection

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Figure 8: Expression of Egr-1 protein in the thymus. Thin sections of normal thymus (A–C) or MHC knockout thymus (D) were fixed in formaldehyde and stained with a specific rabbit anti-Egr-1 peptide antiserum (A, C, D) or the same antibody preincubated with specific peptide (B). Regions of cortex (C) and medulla (M) are indicated. Sections were counterstained with hematoxylin and photographed at ×20 (A, B) or ×40 (C, D). C shows a magnification of the same section photographed in A.
Mentions: To determine the location of cells within the thymus that express Egr-1 protein, thin sections of normal thymus were stained with a specific anti–Egr-1 peptide antiserum (Fig. 8). Isolated cells scattered throughout the cortex were found to express Egr-1. No enrichment of Egr-1 expressing cells in the subcapsular region or cortico-medullary junction was observed. These results are consistent with induction of Egr-1 in cortical double positive thymocytes as a result of TCR engagement. Most, but not all, medullary cells also stained, indicating that Egr-1 protein is expressed in a substantial number of single positive thymocytes as well (see below). In contrast, few cells stained in the thymic cortex of MHC-deficient mice, and in general the staining was weak, even in medullary regions (Fig. 8).

Bottom Line: A similar pattern of expression is found for family members Egr-2 and Egr-3.In contrast, the calcineurin inhibitor cyclosporin A, which inhibits DPK cell differentiation as well as positive selection, inhibits expression of Egr-2 and Egr-3, but not Egr-1.The identification of the Egr family in this context represents the first report of a link between the two known signaling pathways involved in positive selection and downstream transcriptional regulators.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, The Scripps Research Institute, La Jolla, California 92037, USA.

ABSTRACT
There is little known about the regulation of gene expression during TCR-mediated differentiation of immature CD4+8+ (double positive) thymocytes into mature T cells. Using the DPK CD4+8+ thymocyte precursor cell line, we demonstrate that the early growth response-1 gene (Erg-1), encoding a zinc finger transcription factor, is rapidly upregulated after TCR stimulation. We also report that Egr-1 is expressed by a subset of normal double positive thymocytes in the thymic cortex, as well by a majority of medullary single positive thymocytes. Expression of Egr-1 is dramatically reduced in the thymus of major histocompatibility complex knockout mice, but can be induced by anti-CD3 antibody stimulation of isolated thymocytes from these animals. These and other data suggest that high level expression of Egr-1 in the thymus is a consequence of selection. A similar pattern of expression is found for family members Egr-2 and Egr-3. Using the DPK cell line, we also demonstrate that expression of Egr-1, 2, and 3 is dependent upon ras activation, as is the initiation of differentiation to a single positive cell. In contrast, the calcineurin inhibitor cyclosporin A, which inhibits DPK cell differentiation as well as positive selection, inhibits expression of Egr-2 and Egr-3, but not Egr-1. The identification of the Egr family in this context represents the first report of a link between the two known signaling pathways involved in positive selection and downstream transcriptional regulators.

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