Gene transcription in differentiating immature T cell receptor(neg) thymocytes resembles antigen-activated mature T cells.

Abstract

SummaryEarly in ontogeny thymocytes have a surface marker phenotype that resembles activated mature T cells but they lack expression of the T cell receptor (TCR) complex. We have made preparations of day 14/15 triple negative fetal thymocytes that exhibit the activated T lymphocyte markers CD25, intercdlular adhesion molecule 1, Ly-6A/E, CD44, and heat stable antigen and are rapidly proliferating as evidenced by flow cytometric examination of BrdU incorporation. We found that binding activities of the gene regulators nuclear factor (NF)-gB, the NF-gB p50 homodimer complex, nuclear factor of activated T cells (NF-AT), oct-l, oct-2, activator protein 1 (AP-1), and serum response factor (SRF), are all present in these early thymocytes. Whereas the octamer factors and SRF persist during ontogeny, NF-gB, NF-AT, and AP-1 decrease and are undetectable in the adult thymus. Transfection of disaggregated thymocytes by dectroporation or intact thymic lobes by gold-particle bombardment revealed that reporter constructs for NF-gB, NF-AT, AP-1, octamer factors and, to a small extent, the TCR-ot enhancer were active in early thymocyte development. We rigorously diminated the possibility that these transcriptional events were due to minor populations of TCR + cells by showing that these reporter constructs were also active in recombinase activating gene (RAG) -/. thymocytes that are incapable of completing TCR gene rearrangement, and predominantly contain cells that have an activated phenotype. Thus, transcriptional events that are usually triggered by antigen stimulation in mature T cells take place early in thymic ontogeny in the absence of the TCR. Our analysis suggests that there are striking regulatory similarities but also important differences between the activation processes that take place in antigen-stimulated mature T cells and thymic progenitor cells.

Regulation of AP-1 and NFAT Transcription Factors during Thymic Selection of T Cells

“…Indeed, DN thymocytes from the adult thymus are able to produce IL-2 and other cytokines in response to a TcR-independent stimulation (36,68). However, as thymocytes reach the DP stage, they can no longer produce cytokines upon stimulation (9,11,48).…”

“…The specific regulation of these transcription factors has been well studied during T-cell activation, but relatively little is known about the regulation during fetal (29,68) and adult (11,48,56) thymic development. Interestingly, Zúñiga-Pflücker et al showed that both AP-1 and NFAT are functional in DN thymocytes (68).…”

“…Around days 14 to 15 of gestation, fetal thymocytes are predominantly DN CD4 Ϫ CD8 Ϫ TcR Ϫ cells that express mRNAs for interleukin-1␤ (IL-1␤), IL-4, IL-5, IL-6, IL-7, gamma interferon, tumor necrosis factor, and IL-2 and also exhibit surface markers of activated T lymphocytes such as CD25 or CD44 (9,18,38,68). Although resting triple-negative thymocytes from adult mice do not express any cytokines, expression can be induced by TcR-independent stimulation with phorbol esters and calcium ionophore (68). However, as these cells approach the DP stage, there is a striking loss in the ability to produce cytokines (11,36,48).…”

A conserved sequence block in the murine and human T cell receptor Jα loci interacts with developmentally regulated nucleoprotein complexes in vitro and associates with GATA-3 and Octamer-binding factors in vivo

“…The POU family members Oct-1/Oct-2 were shown to interact specifically with a B cell-specific coactivator Bob 1 and this interaction was the main determinant for B cell-specific activation of Ig promoters [31]. It was also shown that expression of the Oct-2 gene is involved in T cell activation and thymocyte development [32][33][34]. In this study we detected differential interactions of Oct-1 and Oct-2 with CSB both in vivo and in vitro in the thymus.…”

Hematopoietic lineage commitment: Role of transcription factors

“…NF-AT is transiently expressed in triple negative thymocytes and later in mature T cells following cell activation via the T cell receptor complex. The presence of an activated phenotype by these early T cell receptor negative thymocytes is attributed to an activation event likely mediated by a thymocyte-stromal cell interaction [119]. The early expression of NF-AT may be crucial for thymocyte development.…”