Project description:Foxp3 is the master transcription factor for the regulatory T cells (Tregs). Alternative splicing of human Foxp3 results in the expression of two isoforms: the full-length and an exon 2-deleted protein. Here, AlphaFold2 predictions and in vitro experiments demonstrate that the N-terminal domain of Foxp3 inhibits DNA binding by moving toward the C-terminus and that this movement is mediated by exon 2. Consequently, we find Foxp3∆2-bearing tTregs in the peripheral lymphoid organ are less sensitive to TCR due to the enhanced binding of Foxp3∆2 to the Batf promoter and are unsusceptible to IL-2. In contrast, among RORγt+ pTregs in the large intestine, Foxp3∆2 pTregs express much more RORγt-related genes conferring a competitive advantage. Together, our results reveal that alternative splicing of exon 2 generates a constitutively active form of Foxp3, which plays a differential role in regulating tTregs and pTregs homeostasis.
Project description:Differing from the mouse Foxp3 gene that encodes only one protein product, human FOXP3 encodes two major isoforms through alternative splicing – a longer isoform (FOXP3 FL) containing all the coding exons and the other shorter isoform lacking the amino acids encoded by exon 2 (FOXP3 ΔE2). The two isoforms are naturally expressed in humans yet their differences in controlling regulatory T cell phenotype and functionality remains unclear. Here we show that patients expressing only the shorter isoform failed to maintain self-tolerance and developed IPEX syndrome. Mice with Foxp3 exon 2 deletion developed excessive TFH and GC B cell responses and systemic autoimmune disease with anti-dsDNA and anti-nuclear autoantibody production and immune-complex glomerulonephritis. Regulatory T cells expressing FOXP3 ΔE2 were unstable and sufficient to induce autoimmunity when transferred into Tcrb-deficient mice. Mechanistically, FOXP3 ΔE2 isoform allows increased expression of selected cytokines but decreased expression of a set of Foxp3 positive regulators without altered binding to these gene loci. We demonstrate that exon 2 of FOXP3 is required to maintain Treg stability and immune homeostasis.
Project description:Differing from the mouse Foxp3 gene that encodes only one protein product, human FOXP3 encodes two major isoforms through alternative splicing – a longer isoform (FOXP3 FL) containing all the coding exons and the other shorter isoform lacking the amino acids encoded by exon 2 (FOXP3 ΔE2). The two isoforms are naturally expressed in humans yet their differences in controlling regulatory T cell phenotype and functionality remains unclear. Here we show that patients expressing only the shorter isoform failed to maintain self-tolerance and developed IPEX syndrome. Mice with Foxp3 exon 2 deletion developed excessive TFH and GC B cell responses and systemic autoimmune disease with anti-dsDNA and anti-nuclear autoantibody production and immune-complex glomerulonephritis. Regulatory T cells expressing FOXP3 ΔE2 were unstable and sufficient to induce autoimmunity when transferred into Tcrb-deficient mice. Mechanistically, FOXP3 ΔE2 isoform allows increased expression of selected cytokines but decreased expression of a set of Foxp3 positive regulators without altered binding to these gene loci. We demonstrate that exon 2 of FOXP3 is required to maintain Treg stability and immune homeostasis.
Project description:The investigation of spliceosomal processes is currently a topic of intense research in molecular biology. In the molecular mechanism of alternative splicing, a multi-protein–RNA complex – the spliceosome – plays a crucial role. To understand the biological processes of alternative splicing, it is essential to comprehend the biogenesis of the spliceosome.
In this paper, we propose the first abstract model of the regulatory assembly pathway of the human spliceosomal subunit U1. Using Petri nets, we describe its highly ordered assembly that takes place in a stepwise manner.
Project description:The rate of RNA polymerase II (pol II) elongation can influence splice site selection in nascent transcripts, yet the extent and physiological relevance of this kinetic coupling between transcription and alternative splicing is not well understood. We performed experiments to perturb pol II elongation and then globally compared alternative splicing patterns with genome-wide pol II occupancy. RNA binding and RNA processing functions were significantly enriched among the genes with pol II elongation inhibition-dependent changes in alternative splicing. Under conditions that interfere with pol II elongation, including cell stress, increased pol II occupancy was detected in the intronic regions flanking the alternative exons in these genes, and these exons generally became more included. A disproportionately high fraction of these exons introduced premature termination codons that elicited nonsense-mediated mRNA decay (NMD), thereby further reducing transcript levels. Our results provide evidence that kinetic coupling between transcription, alternative splicing and NMD affords a rapid mechanism by which cells can respond to changes in growth conditions, including cell stress, to coordinate the levels of RNA processing factors with mRNA levels. To monitor pol II distributions, chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-Seq) was performed using an anti-pol II antibody (4H8) and cross-linked chromatin preparations from Jurkat cells, treated with or without pol II elongation inhibitor 5,6-dichloro-1-β-D-ribofuranosyl-benzimidazole (DRB) at 10 and 25 ug/ml respectively prior to phorbol 12-myristate 13-acetate (PMA) stimulation, for 5000+ alternative splicing events.
Project description:Complex functional coupling exists between transcriptional elongation and pre-mRNA alternative splicing. Pausing sites and changes in the rate of transcription by RNAPII may therefore have a fundamental impact in the regulation of alternative splicing. Here, we show that the elongation and splicing-related factor TCERG1 regulates alternative splicing of the apoptosis gene Bcl-x in a promoter-dependent manner. TCERG1 promotes the splicing of the short isoform of Bcl-x (Bcl-xs) through the SB1 regulatory element located in the first half of exon 2. Consistent with these results, we show evidence for in vitro and in vivo interaction of TCERG1 with the Bcl-x pre-mRNA. Transcription profile analysis reveals that the RNA sequences required for the effect of TCERG1 on Bcl-x alternative splicing coincide with a putative polymerase pause site. Furthermore, TCERG1 modifies the impact of a slow polymerase on Bcl-x alternative splicing. In support of a role for an elongation mechanism in the transcriptional control of Bcl-x alternative splicing, we found that TCERG1 modifies the amount of pre-mRNAs generated at distal regions of the endogenous Bcl-x. Most importantly, TCERG1 affects the rate of RNAPII transcription of endogenous human Bcl-x. We propose that TCERG1 modulates the elongation rate of RNAPII to relieve pausing, thereby activating the pro-apoptotic Bcl-xS 5’ splice site. ChIP-Seq
Project description:Alternative polyadenylation has been implicated as an important regulator of gene expression. In some cases, alternative polyadenylation is known to couple with alternative splicing to influence last intron removal. However, it is unknown whether alternative polyadenylation events influence alternative splicing decisions at upstream exons. Knockdown of the polyadenylation factors CFIm25 or CstF64 was used as an approach in identifying alternative polyadenylation and alternative splicing events on a genome-wide scale. Although hundreds of alternative splicing events were found to be differentially spliced in the knockdown of CstF64, genes associated with alternative polyadenylation did not exhibit an increased incidence of alternative splicing. These results demonstrate that the coupling between alternative polyadenylation and alternative splicing is usually limited to defining the last exon. The striking influence of CstF64 knockdown on alternative splicing can be explained through its effects on UTR selection of known splicing regulators such as hnRNP A2/B1, thereby indirectly influencing splice site selection. We conclude that changes in the expression of the polyadenylation factor CstF64 influences alternative splicing through indirect effects. HeLa cell line was stably transfected with shRNA plasmids targeting CstF64. Total RNA was isolated from CstF64 KD cells and wild-type control cells using Trizol according to manufacturerâs protocols. Samples were deep sequenced in duplicate using the Illumina GAIIx system.
Project description:Autoimmune disease is caused by environmental and genetic factors. Genetic factors associated with increased susceptibility to multiple sclerosis (MS), an autoimmune disease of the central nervous system, have been identified, but their mechanisms of action are incompletely understood.(Briggs, 2019) We previously established that the association between MS risk and the interleukin-7 receptor-a gene (IL7R) is mediated by alternative splicing of IL7R transcripts.(Gregory et al., 2007) This splicing is regulated by the RNA helicase DEAD Box Polypeptide 39B (DDX39B), which shows genetic and functional epistasis with IL7R in enhancing MS risk (Galarza-Munoz et al., 2017). Here we discover that DDX39B, which is also known by immunologists as BAT1 (Spies et al., 1989), impacts the expression of many genes likely to play roles in autoimmunity.(Allcock et al., 2001; Degli-Esposti et al., 1992) We show that DDX39B controls expression of Forkhead Box P3 (FOXP3), a master regulator of the development, maintenance and function of CD4+/CD25+ T regulatory cells(Georgiev et al., 2019; Josefowicz et al., 2012) and repressor of autoimmunity (Bennett et al., 2001; Brunkow et al., 2001; Chatila et al., 2000; Wildin et al., 2001). Splicing of FOXP3 introns, which belong to a new subclass of introns with C-rich polypyrimidine tracts, was exquisitely sensitive to DDX39B levels, making FOXP3 expression highly sensitive to the levels of this RNA helicase. Low DDX39B levels in primary human T regulatory cells lead to loss of regulatory gene expression and cytokine signatures and gain of effector ones. Given the importance of FOXP3 in autoimmunity, this work cements DDX39B as a critically important guardian of immune tolerance that can reduce autoimmune disease risk by regulating IL7R splicing and upregulating FOXP3.