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The requirement for pre-TCR during thymic differentiation enforces a developmental pause that is essential for V-DJβ rearrangement.

Hathcock KS, Farrington L, Ivanova I, Livak F, Selimyan R, Sen R, Williams J, Tai X, Hodes RJ - PLoS ONE (2011)

Bottom Line: We demonstrate that if cells exit the DN3 developmental stage before TCRβ rearrangement occurs, V-DJβ rearrangement never occurs, even in DP cells that are permissive for D-Jβ and TCRα rearrangement.These results demonstrate that pre-TCR expression is not essential for thymic differentiation to DP cells or for V-DJβ suppression.However, the requirement for pre-TCR signals and the exclusion of alternative stimuli such as CD28 enforce a developmental "pause" in early DN3 cells that is essential for productive TCRβ rearrangement to occur.

View Article: PubMed Central - PubMed

Affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America. hathcock@exchange.nih.gov

ABSTRACT
T cell development occurs in the thymus and is critically dependent on productive TCRβ rearrangement and pre-TCR expression in DN3 cells. The requirement for pre-TCR expression results in the arrest of thymocytes at the DN3 stage (β checkpoint), which is uniquely permissive for V-DJβ recombination; only cells expressing pre-TCR survive and develop beyond the DN3 stage. In addition, the requirement for TCRβ rearrangement and pre-TCR expression enforces suppression of TCRβ rearrangement on a second allele, allelic exclusion, thus ensuring that each T cell expresses only a single TCRβ product. However, it is not known whether pre-TCR expression is essential for allelic exclusion or alternatively if allelic exclusion is enforced by developmental changes that can occur in the absence of pre-TCR. We asked if thymocytes that were differentiated without pre-TCR expression, and therefore without pause at the β checkpoint, would suppress all V-DJβ rearrangement. We previously reported that premature CD28 signaling in murine CD4(-)CD8(-) (DN) thymocytes supports differentiation of CD4(+)CD8(+) (DP) cells in the absence of pre-TCR expression. The present study uses this model to define requirements for TCRβ rearrangement and allelic exclusion. We demonstrate that if cells exit the DN3 developmental stage before TCRβ rearrangement occurs, V-DJβ rearrangement never occurs, even in DP cells that are permissive for D-Jβ and TCRα rearrangement. These results demonstrate that pre-TCR expression is not essential for thymic differentiation to DP cells or for V-DJβ suppression. However, the requirement for pre-TCR signals and the exclusion of alternative stimuli such as CD28 enforce a developmental "pause" in early DN3 cells that is essential for productive TCRβ rearrangement to occur.

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Model: The requirement for pre-TCR signaling enforces an essential pause in DN cell development.
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pone-0020639-g007: Model: The requirement for pre-TCR signaling enforces an essential pause in DN cell development.

Mentions: These findings support a novel model for pre-TCR function in thymic development and V-DJβ recombination (Figure 7). During conventional pre-TCR-dependent differentiation TCRβ is rearranged in early DN3 cells, so that proliferation and concomitant down-regulation of both RAG expression and 5′ Vβ locus accessibility do not occur until after productive TCRβ rearrangement is complete and pre-TCR is expressed in late DN3 cells. Thus, early DN3 represents a developmental stage that is uniquely permissive for TCRβ rearrangement because of both high level RAG expression and TCRβ locus accessibility. If proliferation and differentiation are initiated in early DN3 cells prior to successful V-DJβ rearrangement, cells exit this uniquely permissive developmental stage and are not able to complete V-DJβ rearrangement during any subsequent differentiation stage. In contrast, the requirement for pre-TCR signaling to initiate differentiation of DN3 cells enforces an essential “pause” at this developmental stage which is uniquely permissive for V-DJβ rearrangement. This model emphasizes not only the importance of a pause at the DN3 stage that is permissive for TCRβ rearrangement, but also the necessity of preventing expression of other signaling molecules, such as CD28, which are capable of accelerating DN to DP differentiation, or of otherwise mimicking the effects of pre-TCR signaling, prior to V-DJβ rearrangement. The findings presented here are similar to previous reports demonstrating that transgenic TCR expression promotes development to DP cells and suppresses endogenous V-DJβ rearrangement [32]–[36]. The suppression of endogenous TCRβ rearrangement by TCR transgene in these systems may be mediated either by accelerating normal DN differentiation and/or by mimicking more specific pre-TCR signals that are required to enforce V-DJβ suppression.


The requirement for pre-TCR during thymic differentiation enforces a developmental pause that is essential for V-DJβ rearrangement.

Hathcock KS, Farrington L, Ivanova I, Livak F, Selimyan R, Sen R, Williams J, Tai X, Hodes RJ - PLoS ONE (2011)

Model: The requirement for pre-TCR signaling enforces an essential pause in DN cell development.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3108609&req=5

pone-0020639-g007: Model: The requirement for pre-TCR signaling enforces an essential pause in DN cell development.
Mentions: These findings support a novel model for pre-TCR function in thymic development and V-DJβ recombination (Figure 7). During conventional pre-TCR-dependent differentiation TCRβ is rearranged in early DN3 cells, so that proliferation and concomitant down-regulation of both RAG expression and 5′ Vβ locus accessibility do not occur until after productive TCRβ rearrangement is complete and pre-TCR is expressed in late DN3 cells. Thus, early DN3 represents a developmental stage that is uniquely permissive for TCRβ rearrangement because of both high level RAG expression and TCRβ locus accessibility. If proliferation and differentiation are initiated in early DN3 cells prior to successful V-DJβ rearrangement, cells exit this uniquely permissive developmental stage and are not able to complete V-DJβ rearrangement during any subsequent differentiation stage. In contrast, the requirement for pre-TCR signaling to initiate differentiation of DN3 cells enforces an essential “pause” at this developmental stage which is uniquely permissive for V-DJβ rearrangement. This model emphasizes not only the importance of a pause at the DN3 stage that is permissive for TCRβ rearrangement, but also the necessity of preventing expression of other signaling molecules, such as CD28, which are capable of accelerating DN to DP differentiation, or of otherwise mimicking the effects of pre-TCR signaling, prior to V-DJβ rearrangement. The findings presented here are similar to previous reports demonstrating that transgenic TCR expression promotes development to DP cells and suppresses endogenous V-DJβ rearrangement [32]–[36]. The suppression of endogenous TCRβ rearrangement by TCR transgene in these systems may be mediated either by accelerating normal DN differentiation and/or by mimicking more specific pre-TCR signals that are required to enforce V-DJβ suppression.

Bottom Line: We demonstrate that if cells exit the DN3 developmental stage before TCRβ rearrangement occurs, V-DJβ rearrangement never occurs, even in DP cells that are permissive for D-Jβ and TCRα rearrangement.These results demonstrate that pre-TCR expression is not essential for thymic differentiation to DP cells or for V-DJβ suppression.However, the requirement for pre-TCR signals and the exclusion of alternative stimuli such as CD28 enforce a developmental "pause" in early DN3 cells that is essential for productive TCRβ rearrangement to occur.

View Article: PubMed Central - PubMed

Affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America. hathcock@exchange.nih.gov

ABSTRACT
T cell development occurs in the thymus and is critically dependent on productive TCRβ rearrangement and pre-TCR expression in DN3 cells. The requirement for pre-TCR expression results in the arrest of thymocytes at the DN3 stage (β checkpoint), which is uniquely permissive for V-DJβ recombination; only cells expressing pre-TCR survive and develop beyond the DN3 stage. In addition, the requirement for TCRβ rearrangement and pre-TCR expression enforces suppression of TCRβ rearrangement on a second allele, allelic exclusion, thus ensuring that each T cell expresses only a single TCRβ product. However, it is not known whether pre-TCR expression is essential for allelic exclusion or alternatively if allelic exclusion is enforced by developmental changes that can occur in the absence of pre-TCR. We asked if thymocytes that were differentiated without pre-TCR expression, and therefore without pause at the β checkpoint, would suppress all V-DJβ rearrangement. We previously reported that premature CD28 signaling in murine CD4(-)CD8(-) (DN) thymocytes supports differentiation of CD4(+)CD8(+) (DP) cells in the absence of pre-TCR expression. The present study uses this model to define requirements for TCRβ rearrangement and allelic exclusion. We demonstrate that if cells exit the DN3 developmental stage before TCRβ rearrangement occurs, V-DJβ rearrangement never occurs, even in DP cells that are permissive for D-Jβ and TCRα rearrangement. These results demonstrate that pre-TCR expression is not essential for thymic differentiation to DP cells or for V-DJβ suppression. However, the requirement for pre-TCR signals and the exclusion of alternative stimuli such as CD28 enforce a developmental "pause" in early DN3 cells that is essential for productive TCRβ rearrangement to occur.

Show MeSH
Related in: MedlinePlus