Project description:Endogenous SRSF3 and SRSF4 RNA binding sites were identified genome-wide by iCLIP in P19 BAC trangenic cell lines using GFP-epitope tag.
Project description:The goal of this study is to analyse the transcriptome of control hearts vs hearts lacking SRSF3 expression and to analyse binding preferences of SRSF3 in cardiac myocytes.
Project description:Alternative polyadenylation (APA) refers to the regulated selection of polyadenylation sites (PASs) in transcripts, which affects the length of their 3’ untranslated regions (3’UTRs). APA regulates stage- and tissue-specific gene expression by affecting the stability, subcellular localization or translation rate of transcripts. We have recently shown that SRSF3 and SRSF7, two closely related SR proteins, link APA to mRNA export. However, the underlying mechanism for APA regulation by SRSF3 and SRSF7 remained unknown. Here, we combined iCLIP and 3’-end sequencing to find that both proteins bind upstream of proximal PAS (pPAS), but exert opposing effects on 3’UTR length. We show that SRSF7 enhances pPAS usage in a splicing-independent and concentration-dependent manner by recruiting the cleavage factor FIP1, thereby generating short 3’UTRs. SRSF7-specific domains that are absent in SRSF3 are necessary and sufficient for FIP1 recruitment. SRSF3 promotes long 3’UTRs by maintaining high levels of the cleavage factor Im (CFIm) via alternative splicing. Using iCLIP, we show that CFIm binds before and after the pPASs of SRSF3 targets, which masks them and inhibits polyadenylation. In the absence of SRSF3, CFIm levels are strongly reduced, which exposes the pPASs and leads to shorter 3’UTRs. Conversely, during cellular differentiation, 3’UTRs are massively extended, while the levels of SRSF7 and FIP1 strongly decline. Altogether, our data suggest that SRSF7 acts as a sequence-specific enhancer of pPASs, while SRSF3 inhibits pPAS usage by controlling CFIm levels. Our data shed light on a long-standing puzzle of how one factor (CFIm) can inhibit and enhance PAS usage.
Project description:We report a new method which combines subcellular fractionation to advance sequencing technique iCLIP. In this way we identified the spectrum of interactions of two SR-proteins (SRSF3 and SRSF7) to their target RNAs in different subcellular compartments
Project description:This experiment identifies hnRNP A1 binding sites transcriptome-wide in Hela cells. HeLa cells with inducible expression of T7-tagged hnRNP A1 were grown to approximately 90% confluence and then subject to iCLIP analysis (following the protocol from Huppertz et al. 2014 (iCLIP: protein-RNA interactions at nucleotide resolution)). The iCLIP library was sequenced using Illumina's HighSeq 1500
Project description:To investigate whether the ALKBH5-mediated metabolic changes via demethylation of its target mRNA(s) is important in regulating viral response, we mapped the targeting transcripts and binding sites of ALKBH5 in the virus infected cells and uninfected cells by using iCLIP-seq. Biological replicates of iCLIP-seq confirmed that OGDH is the direct targeting transcript of ALKBH5 and the binding capacity of ALKBH5 to OGDH mRNA was decreased upon viral infection. By combining the ALKBH5-iCLIP-seq results with m6A-seq data, we identified that there are overlapped ALKBH5-iCLIP peaks and m6A-seq peaks on OGDH mRNA. Furthermore, other mRNAs, such as GOT2 mRNA, were also the ALKBH5’s targeting transcripts and m6A demethylation substrates. GOT2 is an important metabolic enzyme well known to be involved in host response to viral infection. These data demonstrated that ALKBH5-mediated metabolic rewiring via demethylation of target OGDH mRNA and other transcripts is important in regulating cellular viral replication.
Project description:Alternative polyadenylation (APA) refers to the regulated selection of polyadenylation sites (PASs) in transcripts, which determines the length of their 3’ untranslated regions (3’UTRs). APA regulates stage- and tissue-specific gene expression by affecting the stability, subcellular localization and translation rate of transcripts. We have recently shown that SRSF3 and SRSF7, two closely related SR proteins, connect APA with mRNA export. The mechanism underlying APA regulation by SRSF3 and SRSF7 remained, however, unknown. Here, we combined iCLIP, RNA-Seq and 3’-end sequencing to find that both proteins bind upstream of proximal PASs (pPASs), yet they exert opposite effects on 3’UTR length. We show that SRSF7 enhances pPAS usage in a concentration-dependent but splicing-independent manner by recruiting the cleavage factor FIP1, thereby generating short 3’UTRs. Protein domains unique to SRSF7, which are absent from SRSF3, and hypo-phosphorylation contribute to FIP1 recruitment. In contrast, SRSF3 promotes distal PAS (dPAS) usage and hence long 3’UTRs by maintaining high levels of cleavage factor Im (CFIm) via alternative splicing. Upon reduced expression of SRSF3, CFIm levels strongly decrease and 3’UTRs are globally shortened. In SRSF3-regulated transcripts, CFIm and FIP1 bind upstream of dPASs and promote their usage. Surprisingly, both factors are also recruited to pPASs under conditions where their usage is blocked, suggesting the formation of inactive cleavage complexes. Thus, we identify SRSF3 as a novel regulator of CFIm activity, provide evidence that CFIm inhibits pPAS usage and show that small differences in the domain architecture of SR proteins confer opposite effects on PAS selection.
