Accessibility Control of V(D)J Recombination: Lessons from Gene Targeting

During thymus development, the TCR β locus rearranges before the TCR α locus. Pairing of productively rearranged TCR β-chains with an invariant pTα chain leads to the formation of a pre-TCR and subsequent expansion of immature pre-T cells. Essentially nothing is known about the TCR Vβ repertoire in pre-T cells before or after the expression of a pre-TCR. Using intracellular staining, we show here that the TCR Vβ repertoire is significantly biased at the earliest developmental stage in which VDJβ rearrangement has occurred. Moreover (and in contrast to the VH repertoire in immature B cells), Vβ repertoire biases in immature T cells do not reflect proximity of Vβ gene segments to the DJβ cluster, nor do they depend upon preferential Vβ pairing with the pTα chain. We conclude that V gene repertoires in developing T and B cells are controlled by partially distinct mechanisms.

Section: Possible Origin Of Biased Vdj␤ Recombination In Immature T Cmentioning

confidence: 99%

Section: Possible Origin Of Biased Vdj␤ Recombination In Immature T Cmentioning

confidence: 99%

Biased Vβ Usage in Immature Thymocytes Is Independent of DJβ Proximity and pTα Pairing

Wilson

Maréchal

MacDonald

2001

“…As demonstrated by us and by others (23, 25, 41), deletion of E␤ severely affects V(D)J recombination of cis-linked gene segments, although the precise mechanism(s) by which this effect is mediated is still under investigation. Strikingly, knock-out deletion of enhancer elements from other TCR and Ig genes generally results in a consistent but less severe defect (i.e., V(D)J recombination is decreased at the targeted locus, but production of the corresponding polypeptide and mature lymphocytes in the relevant lineage is not completely abolished (42,43)). This particularity could be related to the fact that, whereas the TCR␤ locus has only one known enhancer, other Ig and TCR loci carry at least two such elements.…”

Section: Essential Role Of E␤ During ␣␤ T Cell Differentiationmentioning

confidence: 99%

T Cell Development in TCRβ Enhancer-Deleted Mice: Implications for αβ T Cell Lineage Commitment and Differentiation

Leduc

Hempel

Mathieu

et al. 2000

Self Cite

T cell differentiation in the mouse thymus is an intricate, highly coordinated process that requires the assembly of TCR complexes from individual components, including those produced by the precisely timed V(D)J recombination of TCR genes. Mice carrying a homozygous deletion of the TCRβ transcriptional enhancer (Eβ) demonstrate an inhibition of V(D)J recombination at the targeted TCRβ locus and a block in αβ T cell differentiation. In this study, we have characterized the T cell developmental defects resulting from the Eβ−/− mutation, in light of previously reported results of the analyses of TCRβ-deficient (TCRβ−/−) mice. Similar to the latter mice, production of TCRβ-chains is abolished in the Eβ−/− animals, and under these conditions differentiation into cell-surface TCR−, CD4+CD8+ double positive (DP) thymocytes depends essentially on the cell-autonomous expression of TCRδ-chains and, most likely, TCRγ-chains. However, contrary to previous reports using TCRβ−/− mice, a minor population of TCR γδ+ DP thymocytes was found within the Eβ−/− thymi, which differ in terms of T cell-specific gene expression and V(D)J recombinase activity, from the majority of TCR−, αβ lineage-committed DP thymocytes. We discuss these data with respect to the functional role of Eβ in driving αβ T cell differentiation and the mechanism of αβ T lineage commitment.

“…Thus, fetal thymocytes were used as a nuclear source for ChIP using specific Abs against acetylated histones. The acetylation of N-terminal lysine residues of histone 3 as well as histone 4, components of the mononucleosomes, are thought to result in an open chromatin structure (2,3,15). Fragmentation of chromatin after cross-linking allowed for specific analysis of small regulatory sequences (average size 200 -500 bp).…”

Section: Hyperacetylation Of Histones At the Tcr␥ Locus In Normal Fetmentioning

confidence: 99%

“…This level of control cannot be explained simply by the presence or absence of the RAG recombinase. Thus it had been postulated that access of the V(D)J recombinase to its target sequence is regulated and that chromatin modifications similar to those required for transcriptional processes participate in this regulation (2,3). In support of this hypothesis, it was reported that transcription of unrearranged gene segments usually precedes V(D)J recombination and the absence of transcriptional regulatory sequences within the TCR locus results in inhibition of recombination.…”

mentioning

confidence: 99%

Cutting Edge: Histone Acetylation and Recombination at the TCRγ Locus Follows IL-7 Induction

Huang

Durum

Muegge

2001

IL-7 signaling is required for V(D)J recombination at the TCRγ locus. We have recently reported that IL-7 controls chromatin accessibility for RAG-mediated cleavage. Inhibition of histone deacetylase substituted for the IL-7 signal, indicating a role for histone acetylation in altering chromatin accessibility. We found a greatly reduced histone 3 and histone 4 acetylation level in IL-7Rα−/− thymocytes in comparison with RAG−/− thymocytes or fetal thymocytes. Sterile transcripts, indicating an open chromatin configuration, were suppressed in IL-7Rα−/− and IL-7−/−RAG−/− thymocytes. Moreover, exogenously added IL-7 induced sterile transcripts from the TCRγ constant region in cultured thymocytes from IL-7−/−RAG−/− mice. This induction correlated with increased histone acetylation at the J-promoter and C-enhancer regulatory elements at the TCRγ locus. These results suggest that IL-7 regulates chromatin accessibility for V(D)J recombination by specifically altering histone acetylation within the TCRγ locus.