Project description:The aim of this study is to analyze the transcriptional effects of Aire deficiency in the thymus, using the Affymetrix MoGene platform to analyze variation in exon usage MECs were isolated from 4-6 wk-old WT or Aire KO ((B6xNOD)F1 background) mice. Three WT and three Aire-KO mice taken individually were used.
Project description:Fezf2 has been implicated in shaping tissue-restricted antigen (TRA) expression and as an “Aire-like” factor in the thymus. Here we demonstrate loss of Fezf2 results primarily in a developmental block in mTEC development with pronounced expansion of Ccl21a-expressing mTECs at the expense of thymic tuft cells and most Aire-high and recently described post-Aire “mimetic” populations. While loss of either Aire or Fezf2 leads to a loss of post-Aire mimetic subtypes, their transcriptional programs are distinct; whereas Aire positively regulates the expression of thousands of genome-wide targets, Fezf2 orchestrates a restricted transcriptional program balanced between induction and repression that largely impacts TEC development. Strikingly, most Fezf2-repressed genes map to Ccl21a-expressing mTECs, suggesting Fezf2 maintains a cellular state conducive to the development of Aire-expressing mTECs and downstream access to terminally differentiated mimetic programs. At least some mimetic cell programs appear to have functions beyond simply serving as antigen reservoirs; thymic microfold cells (M cells) organize the medullary B cell niche in a Ccr6-dependent manner and promote IgA class-switching, analogous to Peyer’s Patches. In Aire and Fezf2 KO mice, where development of thymic M cells is impaired, B cell class-switching is similarly disrupted. Therefore, our data reveal Fezf2 as a gatekeeper of mTEC terminal development which cooperates with Aire to allow the full program of medullary epithelial diversity, supporting unexpected layers of mimetic cell function that impact thymic homeostasis beyond antigen diversity.
Project description:Background: In order to become functionally competent but harmless mediators of the immune system, T cells undergo a strict educational program in the thymus, where they learn to discriminate between self and non-self. This educational program is, to a large extent, mediated by medullary thymic epithelial cells (mTECs) that have a unique capacity to express, and subsequently present a large fraction of body antigens. While the scope of promiscuously expressed genes by mTECs is well established, relatively little is known about the expression of variants that are generated by co- and post-transcriptional processes. Results: Our study reveals that in comparison to other cell types, mTECs display significantly higher levels of alternative splicing, as well as A-to-I and C-to-U RNA editing, which thereby further expand the diversity of their self-antigen repertoire. Interestingly, Aire, the key mediator of mTECs promiscuous gene expression, plays a limited role in the regulation of these transcriptional processes. Conclusions: Our results highlight RNA processing as another layer by which the immune system assures a comprehensive self-representation in the thymus which is required for the establishment of self-tolerance and prevention of autoimmunity. Identification of the number of genes expressed in Aire-KO MEChi
Project description:The aim of this study is to analyze the transcriptional effects of Aire deficiency in the thymus, using the Affymetrix MoGene platform to analyze variation in exon usage
Project description:The deficiency of Aire, a transcriptional regulator whose defect results in the development of autoimmunity, is associated with reduced expression of tissue-restricted self-Ags (TRAs) in medullary thymic epithelial cells (mTECs). Although the mechanisms underlying Aire-dependent expression of TRAs need to be explored, the physical identification of the target(s) of Aire has been hampered by the low and promiscuous expression of TRAs. We have tackled this issue by engineering mice with augmented Aire expression. Integration of the transcriptomic data from Aire-augmented and Aire-deficient mTECs revealed that a large proportion of so-called Aire-dependent genes, including those of TRAs, may not be direct transcriptional targets downstream of Aire. Rather, Aire induces TRA expression indirectly through controlling the heterogeneity of mTECs, as revealed by single-cell analyses. In contrast, Ccl25 emerged as a canonical target of Aire, and we verified this both in vitro and in vivo. Our approach has illuminated the Aire?s primary targets while distinguishing them from the secondary targets.
Project description:Eos, a member of the Ikaros family of transcription factors, is expressed by T regulatory cells (Tregs) and has been postulated to play a role in Treg suppression and maintenance of Treg stability. We demonstrate that expression of Eos was limited to a subpopulation of thymus-derived, activated Tregs and is undetectable in resting or activated T conventional cells (Tconvs). Eos associates with Helios, Foxp3 and Hdac1 and binds directly to the CD25 locus at a site identical to the Foxp3 binding site resulting in enhancement of CD25 expression. Studies in heterozygous female mice demonstrate that Eos is critical for Treg survival and activation. Eos+ Tregs also represent the major population of recirculating thymic Tregs, in which Eos plays a critical role in regulating their migration and suppression of Treg precursors in the thymus by competing for IL-2 and depleting MHC II from thymic dendritic cells (DCs).
Project description:Promiscuous gene expression (pGE) of numerous self-antigens in thymic epithelial cells (TEC) enables the elimination of self-reactive T cells. The autoimmune regulator (Aire) is the only known molecular determinant driving pGE in the thymus but the existence of Aire-independent mechanisms has been inferred. Here, we analyzed the poly(A)+ transcriptome of TEC populations by RNA-sequencing (RNA-seq) in order to reveal differential features of Aire-induced vs. –independent pGE. We report an unanticipated effect of Aire deletion on the proliferation and differentiation of cortical TEC. Moreover, the RNA-seq data reveal the breath of Aire-induced and –independent pGE in medullary TEC (mTEC) subsets and the extent of thymic peripheral tissue representation. The results suggest that Aire-induced promiscuously expressed transcripts affect several functions with far reaching biological consequences in mTEC. High-throughput characterization of TEC transcriptomes will enable progress in understanding TEC biology and the establishment of self-tolerance. The mRNA profiles of cTEC, mTEClo and mTEChi from 6-8 week-old wild type (WT) and Aire-/- (KO) mice were generated by RNA-sequencing using Illumina HiSeq2000.