Molecular analysis of the mechanisms linking co-transcriptional splicing with chromatin

Lead Research Organisation: John Innes Centre
Department Name: UNLISTED

Abstract

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Technical Summary

The project will exploit recent work in Arabidopsis (in the Dean laboratory) linking RNA metabolism and chromatin silencing (Liu et al 2009). The Dean group is focused on RNA-mediated chromatin regulation of an important repressor of flowering called FLOWERING LOCUS C (FLC). The concepts that have emerged from this study have wide relevance in many organisms. Conserved RNA 3’ processing factors function with an RNA-binding protein to target polyadenylation to a specific site in
the FLC antisense transcript. This 3’ processing event triggers histone demethylation and transcriptional silencing of the locus. Their unpublished work shows that a conserved splicing factor, specifically PRP8, a core component of the spliceosome, also functions in this mechanism. The overall aim of the proposal is to reveal the molecular mechanism of involvement of splicing factor PRP8 on anti-sense RNA dependent regulation of transcription of FLC in Arabidopsis and to test generality of that mechanism on other anti-sense regulated genes.
The specific objectives of the proposal include:
1.Fully characterizing the FLC antisense transcript changes in the splicing factor mutant (prp8) mutant.
2.Analysing the contributions of RNA degradation pathways in the accumulation of FLC antisense transcripts in wild type and in prp8 mutant backgrounds.
3.Analysing the interactions between splicing and 3’ processing of the antisense transcripts.
4.Generating and analysing directed mutations in PRP8 to explore whether the prp8 allele generated in the forward mutant screen is hypomorphic or has lost a specific function but is still wild-type for generic splicing functions.
5.Analysing the components of the RNP complex that are assembled on the antisense transcript.
A better understanding of the flowering control of the agricultural crops is fully in line with goals of research in the FP7 first priority thematic areas, such as Food, Agriculture and Biotechnology and Environment including climate changes.

Planned Impact

unavailable

Publications

10 25 50
 
Description The Dean lab is focused on understanding the mechanism of regulation of FLOWERING LOCUS C (FLC) gene expression, which encodes an important flowering regulator in the model plant Arabidopsis thaliana as well as in commercially important Brassicaceae species. FLC expression is regulated by long antisense non-coding RNAs collectively named COOLAIR, which are expressed from the FLC locus. There are two major forms of COOLAIR resulting from alternative polyadenylation - termed proximal and distal COOLAIR. The project funded by this fellowship pursued the role of a central component of the spliceosome, PRP8 in this mechanism.

The project characterized the interactions between the sense and antisense transcription of FLC to understand how one component of the RNA spliceosome, PRP8 impacted this interaction. Complete inactivation of the PRP8 gene is lethal in Arabidopsis thaliana. The prp8 mutation discovered in the FLC regulator forward mutagenesis screen was not lethal, but exhibited delayed flowering. Our hypothesis was that this hypomorphic (partial effect) mutation might affect splicing efficiency and to test this we performed a comprehensive assessment of splicing efficiency of the sense and antisense introns at the FLC locus. Our results showed that the hypomorphic prp8 mutation specifically reduced splicing efficiency of the short version of the antisense intron and this resulted in reduced formation of the short "proximal" antisense transcript. Thus, in the wild-type context PRP8 appears to promote splicing of the short antisense intron that, in turn, promotes use of the proximal antisense polyadenylation site and thus represses sense FLC transcription.
To assess the degree of COOLAIR regulation on FLC transcription we transformed Arabidopsis flc mutant plants with a construct that expresses sense FLC, but is disrupted in COOLAIR expression. Interestingly, the transformants exhibited increased levels of unspliced sense FLC and the prp8 mutation no longer affected FLC expression. These data suggest that antisense transcription is important for PRP8 repression of FLC expression.
Next we directly assessed the effect of splicing and polyadenylation of proximal COOLAIR on FLC sense expression. We focussed on the proximal intron that was inefficiently spliced in the prp8 mutant. We prevented use of the first intron 3' splice site in this transcript by mutating the dinucleotide splice site AG to AA. This construct was then introduced into flc mutant plants that did or did not carry the prp8 mutation. We found that the 3' splice site mutation was sufficient to significantly increase levels of FLC sense expression. Moreover, this mutation was associated with lower levels of proximal antisense polyadenylation.

In summary, we have revealed the mechanism by which PRP8 represses sense FLC expression and showed it is involved in altered splicing and polyadenylation of an antisense transcript that in turn regulates sense strand transcription. Given that pervasive transcription has been detected in many genomes this work has the potential to inform regulation of transcription in many organisms.
Exploitation Route Conceptual understanding will be relevant for all researchers studying transcription
Sectors Agriculture

Food and Drink

Environment

 
Description GCRF databases and Resources phase 2
Amount £98,000 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 11/2017 
End 07/2018
 
Description Mechanistic basis of nucleation and spreading underlying a Polycomb-mediated epigenetic switch (EPISWITCH)
Amount € 2,100,000 (EUR)
Funding ID 833254 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 08/2019 
End 09/2024
 
Description Invited lecture at the Institute Structural and Molecular Biology, Birkbeck College/UCL. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Prof Caroline Dean was invited to give a lecture about epigenetic switching entitled: ""Sensing and Remembering Winter" at the Institute Structural and Molecular Biology, Birkbeck College/UCL.
Year(s) Of Engagement Activity 2016
 
Description Invited seminar at CAS Plant Stress Centre, Shanghai, China 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Prof Caroline Dean was invited to give a seminar at the CAS Plant Stress Centre, Shanghai, China. Her talk was entitled: "Antisense-mediated chromatin silencing at FLC".
Year(s) Of Engagement Activity 2016
 
Description Invited seminar in Beijing, China 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Prof Caroline Dean was invited to give a seminar in Beijing, China. The talk was entitled: "Antisense-mediated chromatin silencing at FLC".
Year(s) Of Engagement Activity 2016
 
Description Invited speaker at the EMBO Non-coding RNA meeting, Heidelberg. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Prof Caroline Dean was invited speaker at the EMBO Non-coding RNA meeting in Heidelberg. Talk title: "Antisense-mediated chromatin silencing at FLC".
Year(s) Of Engagement Activity 2016
 
Description Seminar as part of the Tsinghua University Seminar in Frontiers in Biology special series. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Prof Caroline Dean gave a seminar as part of the Tsinghua University Seminar in Frontiers in Biology special series entitled: "Antisense-mediated chromatin silencing at FLC".
Year(s) Of Engagement Activity 2016