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Lineage commitment in the thymus: only the most differentiated (TCRhibcl-2hi) subset of CD4+CD8+ thymocytes has selectively terminated CD4 or CD8 synthesis.

Punt JA, Suzuki H, Granger LG, Sharrow SO, Singer A - J. Exp. Med. (1996)

Bottom Line: However, the molecular event(s) that defines lineage commitment is controversial.The present study supports such a molecular definition by showing that termination of either CD4 or CD8 synthesis is a highly regulated event that is only evident within the most differentiated DP subset (CD5hiCD69hiTCRhibcl-2hi).In fact, essentially all cells within this DP subset actively synthesize only one coreceptor molecule.

View Article: PubMed Central - PubMed

Affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.

ABSTRACT
Lineage commitment is a developmental process by which individual CD4+CD8+ (double positive, DP) thymocytes make a decision to differentiate into either CD4+ or CD8+ T cells. However, the molecular event(s) that defines lineage commitment is controversial. We have previously proposed that lineage commitment in DP thymocytes can be molecularly defined as the selective termination of CD4 or CD8 coreceptor synthesis. The present study supports such a molecular definition by showing that termination of either CD4 or CD8 synthesis is a highly regulated event that is only evident within the most differentiated DP subset (CD5hiCD69hiTCRhibcl-2hi). In fact, essentially all cells within this DP subset actively synthesize only one coreceptor molecule. In addition, the present results identify three distinct sub-populations of DP thymocytes that define the developmental progression of the lineage commitment process and demonstrate that lineage commitment is coincident with upregulation of TCR and bcl-2. Thus, this study supports a molecular definition of lineage commitment and uniquely identifies TCRhibcl-2hi DP thymocytes as cells that are already committed to either the CD4 or CD8 T cell lineage.

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Related in: MedlinePlus

Selective termination of coreceptor synthesis requires  TCRαβ/CD3 expression. (A) CD5 expression of CD4+CD8+ thymocytes from wild-type and TCRα deficient mice was assessed by flow  cytometry. It is evident that the CD5hi CD4+CD8+ thymocyte subpopulation is absent in TCRα-deficient mice. (B) CD4+CD8lo and CD4lo  CD8+ subpopulations of thymocytes from a TCRα-deficient mouse were  electronically sorted according to the gates indicated and were assessed for  coreceptor synthesis by the coreceptor reexpression assay. Frequency of  cells falling into each quadrant are indicated. No cells that had selectively  terminated CD4 or CD8 synthesis are evident in either population.
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Figure 5: Selective termination of coreceptor synthesis requires TCRαβ/CD3 expression. (A) CD5 expression of CD4+CD8+ thymocytes from wild-type and TCRα deficient mice was assessed by flow cytometry. It is evident that the CD5hi CD4+CD8+ thymocyte subpopulation is absent in TCRα-deficient mice. (B) CD4+CD8lo and CD4lo CD8+ subpopulations of thymocytes from a TCRα-deficient mouse were electronically sorted according to the gates indicated and were assessed for coreceptor synthesis by the coreceptor reexpression assay. Frequency of cells falling into each quadrant are indicated. No cells that had selectively terminated CD4 or CD8 synthesis are evident in either population.

Mentions: As an independent test of our conclusion that selective termination of coreceptor synthesis is a developmentally regulated event that only occurs in the most differentiated subset of CD5hi DP thymocytes, we examined DP thymocyte populations from TCRα−/− mice that are unable to assemble and express surface TCRαβ complexes and, consequently, lack CD5hi DP thymocytes (Fig. 5 a). In this experiment, we attempted to increase our ability to detect DP thymocytes synthesizing only one coreceptor molecule by performing the coreceptor reexpression assay on purified populations of CD4+8lo and CD4lo8+ transitional DP thymocytes that may be developmentally more advanced than the bulk of DP thymocytes (Fig. 5 b). Even so, we failed to detect any DP thymocytes in TCRα−/− mice that were selectively synthesizing only one coreceptor molecule (Fig. 5 b). Thus, surface expression of TCRαβ/ CD3 complexes and the signals they transduce are required for generation of CD5hi DP thymocytes and for selective termination of a coreceptor molecule.


Lineage commitment in the thymus: only the most differentiated (TCRhibcl-2hi) subset of CD4+CD8+ thymocytes has selectively terminated CD4 or CD8 synthesis.

Punt JA, Suzuki H, Granger LG, Sharrow SO, Singer A - J. Exp. Med. (1996)

Selective termination of coreceptor synthesis requires  TCRαβ/CD3 expression. (A) CD5 expression of CD4+CD8+ thymocytes from wild-type and TCRα deficient mice was assessed by flow  cytometry. It is evident that the CD5hi CD4+CD8+ thymocyte subpopulation is absent in TCRα-deficient mice. (B) CD4+CD8lo and CD4lo  CD8+ subpopulations of thymocytes from a TCRα-deficient mouse were  electronically sorted according to the gates indicated and were assessed for  coreceptor synthesis by the coreceptor reexpression assay. Frequency of  cells falling into each quadrant are indicated. No cells that had selectively  terminated CD4 or CD8 synthesis are evident in either population.
© Copyright Policy
Related In: Results  -  Collection

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Figure 5: Selective termination of coreceptor synthesis requires TCRαβ/CD3 expression. (A) CD5 expression of CD4+CD8+ thymocytes from wild-type and TCRα deficient mice was assessed by flow cytometry. It is evident that the CD5hi CD4+CD8+ thymocyte subpopulation is absent in TCRα-deficient mice. (B) CD4+CD8lo and CD4lo CD8+ subpopulations of thymocytes from a TCRα-deficient mouse were electronically sorted according to the gates indicated and were assessed for coreceptor synthesis by the coreceptor reexpression assay. Frequency of cells falling into each quadrant are indicated. No cells that had selectively terminated CD4 or CD8 synthesis are evident in either population.
Mentions: As an independent test of our conclusion that selective termination of coreceptor synthesis is a developmentally regulated event that only occurs in the most differentiated subset of CD5hi DP thymocytes, we examined DP thymocyte populations from TCRα−/− mice that are unable to assemble and express surface TCRαβ complexes and, consequently, lack CD5hi DP thymocytes (Fig. 5 a). In this experiment, we attempted to increase our ability to detect DP thymocytes synthesizing only one coreceptor molecule by performing the coreceptor reexpression assay on purified populations of CD4+8lo and CD4lo8+ transitional DP thymocytes that may be developmentally more advanced than the bulk of DP thymocytes (Fig. 5 b). Even so, we failed to detect any DP thymocytes in TCRα−/− mice that were selectively synthesizing only one coreceptor molecule (Fig. 5 b). Thus, surface expression of TCRαβ/ CD3 complexes and the signals they transduce are required for generation of CD5hi DP thymocytes and for selective termination of a coreceptor molecule.

Bottom Line: However, the molecular event(s) that defines lineage commitment is controversial.The present study supports such a molecular definition by showing that termination of either CD4 or CD8 synthesis is a highly regulated event that is only evident within the most differentiated DP subset (CD5hiCD69hiTCRhibcl-2hi).In fact, essentially all cells within this DP subset actively synthesize only one coreceptor molecule.

View Article: PubMed Central - PubMed

Affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.

ABSTRACT
Lineage commitment is a developmental process by which individual CD4+CD8+ (double positive, DP) thymocytes make a decision to differentiate into either CD4+ or CD8+ T cells. However, the molecular event(s) that defines lineage commitment is controversial. We have previously proposed that lineage commitment in DP thymocytes can be molecularly defined as the selective termination of CD4 or CD8 coreceptor synthesis. The present study supports such a molecular definition by showing that termination of either CD4 or CD8 synthesis is a highly regulated event that is only evident within the most differentiated DP subset (CD5hiCD69hiTCRhibcl-2hi). In fact, essentially all cells within this DP subset actively synthesize only one coreceptor molecule. In addition, the present results identify three distinct sub-populations of DP thymocytes that define the developmental progression of the lineage commitment process and demonstrate that lineage commitment is coincident with upregulation of TCR and bcl-2. Thus, this study supports a molecular definition of lineage commitment and uniquely identifies TCRhibcl-2hi DP thymocytes as cells that are already committed to either the CD4 or CD8 T cell lineage.

Show MeSH
Related in: MedlinePlus