Defect in Rearrangement of the Most 5′ TCR–Jα Following Targeted Deletion of T Early α (TEA): Implications for TCR α Locus Accessibility

Abstract

To address the role of the TEA germline transcription, which initiates upstream of the TCR-J alpha S, in the regulation of TCR-J alpha locus accessibility, we created a mouse in which this region has been removed by homologous recombination. Normal development of T alpha beta cells and the expression of other TCR alpha germline transcripts in TEA-/- mice ruled out an exclusive role for TEA in the overall accessibility of the J alpha cluster. However, the rearrangement of the most 5' J alpha (J alpha 61 to J alpha 53) was severely impaired, indicating that TEA may control the DNA accessibility of a particular J alpha window. Moreover, the relative usage of every J alpha segment was affected. These results are consistent with TEA acting as a "rearrangement-focusing" element, targeting the primary waves of V alpha-J alpha recombination to the most 5' J alpha S in an ongoing TCR-J alpha rearrangement model.

TEA regulates local TCR‐Jα accessibility through histone acetylation

“…Although V § J § rearrangements have been shown to initiate at the 5´end of the J § cluster, probably targeted by TEA, our data show that in thymocytes the chromatin has been remodeled, both in TEA-dependent and independent windows. This is in accordance with the observation that in the absence of TEA, V § J § rearrangements still occur on downstream J § segments [15].…”

“…2e and f); strikingly, the levels of acetylation were back to normal in the downstream region of the cluster. This 5´window of hypoacetylation overlaps closely with the window of impaired rearrangements and impaired germ-line transcripts observed in the TEA-/-mice [15]. Put together, these results indicate that TEA is required for V § J § rearrangements within this particular window of the J § cluster, possibly through H3 and H4 histones acetylation.…”

“…Such a global accessibility does not account for the gradual usage of the J § segments. We have shown that the TEA element controls the accessibility of the first 9 J § segments and targets the first rearrangements to the 5´end of the cluster on both alleles thus establishing a coincidence between the alleles [15,17]. We thus proposed that TEA confers a hyperaccessibility of the DNA on the 5´end of the J § cluster and in this report we show that the presence of a functional TEA element correlates with a hyperacetylation of histones H4 and H3 in this 5´window.…”

“…At the 3´end of the locus, Enh § controls the global accessibility and acetylation level of the whole TCR § region. Deletion of the TEA element reveals that beyond the global control of Enh § over the entire region, a particular window of J § segments (the 9 most 5´J § in a total of 61) is under the direct control of TEA during the V-J § rearrangements [15]. Furthermore, in the J § cluster, both alleles of the locus are rearranged with a tight interallelic coincidence that relies on the presence of TEA [16,17].…”

Developmental Stage-Specific Regulation of TCR-α-Chain Gene Assembly by Intrinsic Features of the TEA Promoter

“…Analysis of TCR␣ mRNA from TCR␣/␦ 5⌬T/5⌬T and TCR␣/␦ ϩ/ϩ ␣␤ T cells revealed that similar fractions of VJ␣ rearrangements use the J␣58 and J␣57 gene segments, which are located 5Ј in the J␣ gene segment cluster and are dependent on TEA promoter activity for accessibility (Fig. 4B) (22). Together, these data demonstrate that the TEA promoter is intact and regulates transcription and accessibility normally on the TCR␣/␦ 5⌬T allele in DP thymocytes.…”