TCRγ Silencing during αβ T Cell Development Depends upon Pre-TCR-Induced Proliferation

Abstract

During thymus development, immature T cells become committed to two distinct lineages based upon expression of αβ or γδ TCR. In the αβ lineage, developing thymocytes progressively extinguish transcription of the TCRγ genes by a poorly understood process known as γ silencing. We show that αβ lineage thymocytes in mice lacking a functional pre-TCR undergo limited proliferation and fail to silence TCRγ genes during development. Stimulation of pre-TCR-deficient immature thymocytes with anti-CD3 Abs does not directly down-regulate TCRγ transcription but restores TCRγ silencing following proliferation. Collectively our data reveal an important role for pre-TCR induced proliferation in activating the TCRγ silencer in αβ lineage thymocytes, a process that may reinforce αβ or γδ lineage commitment.

A critical lineage‐nonspecific role for pTα in mediating allelic and isotypic exclusion in TCRβ‐transgenic mice

“…In addition to the well-established role of pTa in expansion of ab lineage-committed thymocytes [5,39] and its related (although indirect) role in TCRc silencing [4], we confirm with three independent TCRb Tg mouse lines that pTa is strictly required to mediate allelic exclusion of endogenous TCRb genes and isotypic exclusion of cd cell development. The extent to which pTa influences ab/cd lineage commitment in normal mice by these latter mechanisms remains to be directly established.…”

“…Total RNA was reverse-transcribed using random nonamers and AMV reverse transcriptase (Roche). Genomic DNA was extracted from sorted DN3 cells and quantification of Vc2-Jc1 rearrangements was performed as described [4]. For the PCR reaction, the LightCyclerFastStart DNA Master SYBR Green I kit (Roche) was used following the instruction manual.…”

“…pTa is a critical component of the pre-TCR which consists, in addition, of a functionally rearranged TCRb chain and CD3 signaling components. Signaling through the pre-TCR has been reported to be responsible for many important functions during the development of ab lineage cells, including TCRb allelic exclusion [1-3], TCRc silencing [4], and extensive proliferation during the transition from DN to CD4 + CD8 + double-positive (DP) stages [5]. Since pTa -/-mice have an increased number of cd cells that harbor an increased frequency of in-frame TCRb rearrangements [6], it has also been proposed that the pre-TCR favors ab lineage commitment at the expense of cd cells [6].…”

Breakpoint sites disclose the role of the V(D)J recombination machinery in the formation of T-cell receptor (TCR) and non-TCR associated aberrations in T-cell acute lymphoblastic leukemia

“…Signaling via the pre-TCR, which plays a role in T-ALL development, 71 can activate the TCRG silencer. 72 The apparent lack of TCRG translocations in T-ALL could thus be the result of pre-TCR mediated activation of the TCRG silencer located in cis of the TCRG locus that was involved in a translocation, resulting in dampening of oncogenic activation. It might well be that the positive and negative selection phases of TCRαβ thymocytes are implicated in the low occurrence of TCRA locus translocations seen in T-ALL.…”

Insights into the Transcriptional Regulation of the Unrearranged and Rearranged Tcra and Tcrd Genes

“…During β-selection, pre-TCRmediated signaling triggers the Tcra germline transcription and VJ recombination and the development of αβ T lymphocytes, and inhibits the transcription of the Tcrg and Tcrd loci [13][14][15]. The molecular targets of those signaling pathways are genomic regulatory sequences capable of controlling chromatin structure of the loci, such as the enhancers associated with the Tcrg, Tcrd, and Tcra loci, and the silencer and promoters associated with the Tcrg and Tcrb loci [11,13,14,[16][17][18][19][20][21][22][23][24][25]. …”