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A coilin mutant provides a sensitized system for identifying modifiers of alternative splicing and posttranscriptional gene silencing in Arabidopsis thaliana

ABSTRACT: Coilin is a scaffold protein essential for the structural integrity of Cajal Bodies, which are non-membranous nuclear organelles that are thought to facilitate assembly and maturation of nuclear RNPs, including spliceosomal snRNPs. To investigate further coilin’s functions in plant cells, and to identify proteins that may functionally interact with coilin, we performed a genetic suppressor screen in Arabidopsis thaliana using a coilin (coi) mutant displaying altered splicing of a GFP pre-mRNA. The modified splicing pattern results in a ‘hyper-GFP’ phenotype in young coi seedlings relative to the intermediate level of GFP in wild-type seedlings. Additionally, in newly emerging leaves of older coi seedlings, the GFP gene frequently undergoes abrupt siRNA-associated posttranscriptional gene silencing that persists during growth. In the suppressor screen, we searched for mutations that subdue one or both of these GFP phenotypes and identified several understudied factors in plants: WRAP53, a putative Cajal body protein; SMU2, a predicted splicing-related factor; and ZC3HC1, an uncharacterized zinc finger protein. All three mutations return the hyper-GFP phenotype of the coi mutant to approximately the intermediate wild-type level. The zc3hc1 mutations in particular induce premature and more extensive posttranscriptional gene silencing similar to mutations in SOP1 and DCL4, which are known modifiers of posttranscriptional gene silencing. Candidate coilin-interacting proteins identified by immunoprecipitation-mass spectrometry include many splicing-related factors, nucleolar proteins, and mRNA export factors. Our results demonstrate the usefulness of the coi mutant to identify new modifiers of alternative splicing and posttranscriptional gene silencing, and suggest diverse roles for coilin in plant cells.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Arabidopsis Thaliana (mouse-ear Cress)

TISSUE(S): Whole Body

SUBMITTER: Chuan-Chih Hsu

LAB HEAD: Marjori Matzke

PROVIDER: PXD027146 | Pride | 2023-07-27

REPOSITORIES: Pride

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Project description:MSI (Microsatellite Instability) colorectal cancer (CRC) show improved survival, are less prone to metastasis and show poor response to chemotherapy (compared to MSS tumors). The underlying reasons for these characteristics are still not understood and no specific therapeutic approach for MSI colon tumours (15% of CRC overall) has yet been developed. The MSI process is oncogenic when it affects DNA repeat sequences that have a functional role, e.g. Small Coding Repeats (SCR). MSI also frequently affects Long Non-Coding Repeats (LNCR) in tumour DNA. In contrast to SCR, only a few LNCR are endowed with biological activity. Consequently, this area has received very little attention. Our group recently identified HSP110 mutant chaperone protein in MSI CRC that was generated by somatic deletion of a LNCR. Of interest, HSP110 mutant (due to exon skipping) have anti-oncogenic properties and the survival of MSI CRC patients receiving chemotherapy is positively associated with HSP110 mutations in tumour DNA. The aim of the current project is to identify additional clinically relevant MSI-associated splicing aberrations due to mutations in LNCR located in splice acceptor sites. The four main steps are as follows: 1. To identify exon/intron sites affected by aberrant splicing events due to MSI in CRC . All RNASeq data will be exploited to identify recurrent splicing aberrations (mostly exon skipping) that occur specifically in MSI colon tumours; 2. To investigate for possible functional links between MSI and any detected aberrant splicing events . All specific aberrant splicing events detected by RNAseq in MSI CRC samples will be first confirmed (quantitative RT-PCR) in order to eliminate false positive cases. For validated exon candidates, the allelic profiles of adjacent intronic LNCR will be analysed (PCR and fluorescence genotyping) in CRC cell lines and primary tumours (MSI and MSS), as well as in matching normal mucosa samples in order to assess their polymorphic status; 3. To identify splicing events and LNCR mutations with clinical relevance in MSI CRC patients . All LNCR with a confirmed role in gene splicing in MSI CRC will be analysed. The clinical relevance of candidate genes will be assessed using multivariate survival regression models for Relapse- Free Survival, with interaction terms (response to chemotherapy); 4. To initiate functional studies on a limited number of clinically relevant, cancer-related genes whose splicing is perturbed in MSI cancer cells, and to develop biological tools to simplify screening in future clinical assays Similar to HSP110, we will focus on 4 or 5 mutant proteins that are promising drug therapeutic targets. Functional assays will be developed to further elucidate their role in the pathophysiology of MSI tumours. We also aim to develop biological tools for these candidate genes, such as the detection of wild-type or mutant proteins by immunohistochemistry.

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A coilin mutant provides a sensitized system for identifying modifiers of alternative splicing and posttranscriptional gene silencing in Arabidopsis thaliana

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