| Takayuki Nojima | Last modified date：2024.04.08 |
Associate Professor /
Cancer genome regulation /
Research Center for Systems Immunology /
Medical Institute of Bioregulation
Presentations
| 1. | 野島孝之, Transcription termination: Forgotten mechanism in RNA synthesis cycle, 熊本大学リエゾンラボ/HIGO最先端研究セミナー , 2022.07. |
| 2. | Takayuki Nojima, POINTing towards transcription termination, 第30回 Hot Spring Harbor Symposium、クロマチン潜在能 合同国際シンポジウム , 2022.01, [URL], Transcription is terminated in appropriate region to prevent genome stresses such as transcription-replication conflict and RNA-DNA hybrid caused in extragenic region of eukaryote cells. Biochemical and genetic approaches identified several trans-factors and cis-elements involved in transcription termination. However, the mechanism and the rule remain largely unclear due to technical limitation and complexity created by other co-transcriptional events. In order to investigate precise mechanisms of transcription, we developed a nascent RNA technology named mammalian native elongating transcript-sequencing (mNET-seq) method that reveals Pol II pausing and RNA processing intermediates with the phosphorylation states at single nucleotide resolution. In mNET-seq analysis, RNA polymerase II (Pol II) machinery was specifically detected at termination region of protein coding genes with the CTD phosphorylation at threonine 4 position (T4P). Our group substantially extended mNET-seq method to dissect intact nascent RNA associated with elongating Pol II machinery. This new method was termed Polymerase Intact Nascent Transcript (POINT) technology. The POINT technology is applied to a template switching based 5’RACE method, resulting in detection of nascent transcript 5’ends at single nucleotide resolution (POINT-5) in illumina platform. Therefore POINT-5 method precisely profiles transcription start sites and co-transcriptional RNA cleavage sites. Notably rapid depletion of nuclear 5’-3’ exonuclease Xrn2 significantly induced a termination defect with increased RNA cleavage peaks only on polyadenylation sites of pre-mRNA genes, but not on other cleavage sites. This analysis revealed specificity of Xrn2-dependent RNA turnover. In conclusion, mNET and POINT technology variants will prove invaluable to dissect the termination mechanism not only for pre-mRNA gene, but also other gene category such as noncoding genes.. |
| 3. | Takayuki Nojima, Mechanism of Co-transcriptional RNA splicing, 第16回生命医科学研究所ネットワーク国際シンポジウム＆ KEY FORUM 2021, 2021.11, [URL], In mammalian cells, transcripts synthesised by RNA polymerase II (Pol II) are largely co-transcriptionally (co-T) spliced. The exact timing of intron excision after transcription may influence splice site usage, thus shaping the alternatively spliced transcriptome. However, the underlying splicing kinetics is still poorly understood due to technical limitations in the purification of authentic newly synthesized transcripts (nascent RNA). To overcome this issue, our group have developed mammalian native elongating transcript-sequencing (mNET-seq) technology to analyse nascent RNAs with Pol II phosphorylation states (Nojima et al., Cell 2015). mNET-seq method revealed Pol II pausing on exon and phosphorylated Pol II specific spliceosome assembly (Nojima et al., Mol Cell 2018). Furthermore, we recently developed a new technology to dissect intact nascent RNAs directly purified from all Pol II transcribing states, called Polymerase Intact Nascent Transcript (POINT) (Sousa-Luis et al., Mol Cell 2021). By combining Illumina and Nanopore technologies, we took advantage of the high coverage of the former and the long read lengths of the latter. POINT single-molecule long-read data in human cells revealed the presence of different classes of splicing kinetics. ~40% of analysed introns are immediately excised as soon as the downstream exon emerges from Pol II, whereas many other introns progressively undergo delayed co-T splicing while Pol II transcribes the next intron. Moreover, we found that splicing dynamics relate to the distance between the intron and the 3’ end of the gene. Using engineered cell-lines with auxin-inducible degradation of the endogenous cleavage factor CPSF73 gene, we detected higher levels of splicing in cleavage-deficient cells. Most likely, this is because the transcriptional read-through increased the time available for delayed co-T splicing. Taken together, our novel POINT technology is able to show variation in co-T processing splicing dynamics, suggesting the presence of both immediate and delayed co-T splicing mechanisms.. |
| 4. | Takayuki Nojima, End of RNA synthesis, 日本生化学会, 2021.10, Transcription is terminated in appropriate region to prevent genome stresses such as transcription-replication conflict and RNA-DNA hybrid caused in extragenic region of eukaryote cells. Biochemical and genetic approaches identified several trans-factors and cis-elements involved in transcription termination. However, the mechanism and the rule remain largely unclear due to technical limitation and complexity created by other co-transcriptional events. In order to investigate precise mechanisms of transcription, we developed a nascent RNA technology named mammalian native elongating transcript-sequencing (mNET-seq) method that reveals Pol II pausing and RNA processing intermediates with the phosphorylation states at single nucleotide resolution. In mNET-seq analysis, RNA polymerase II (Pol II) machinery was specifically detected at termination region of protein coding genes with the CTD phosphorylation at threonine 4 position (T4P). On the other hand, the T4P CTD mark is distributed throughout long noncoding RNA (lncRNA) gene units, suggesting transcription termination signals are embedded in lncRNA genes to fine tune lncRNA expression. We substantially extended mNET-seq method to dissect intact nascent RNA associated with elongating Pol II machinery. This new method was termed Polymerase Intact Nascent Transcript (POINT) technology. The POINT technology is applied to a template switching based 5’RACE method, resulting in detection of nascent transcript 5’ends at single nucleotide resolution (POINT-5) in illumina platform. Therefore POINT-5 method precisely profiles transcription start sites and co-transcriptional RNA cleavage sites. Notably rapid depletion of nuclear 5’-3’ exonuclease Xrn2 significantly induced a termination defect with increased RNA cleavage peaks only on polyadenylation sites of pre-mRNA genes, but not on other cleavage sites. This analysis revealed specificity of Xrn2-dependent RNA turnover. In conclusion, mNET and POINT technology variants will prove invaluable to dissect the termination mechanism not only for pre-mRNA gene, but also other gene category such as noncoding genes.. |
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