Department of Bioengineering, University of Pennsylvania, Philadelphia, United States.
School of Life Sciences, Westlake University, Hangzhou, China.
Elife. 2024 Apr 5;12:RP91357. doi: 10.7554/eLife.91357.
Splicing is the stepwise molecular process by which introns are removed from pre-mRNA and exons are joined together to form mature mRNA sequences. The ordering and spatial distribution of these steps remain controversial, with opposing models suggesting splicing occurs either during or after transcription. We used single-molecule RNA FISH, expansion microscopy, and live-cell imaging to reveal the spatiotemporal distribution of nascent transcripts in mammalian cells. At super-resolution levels, we found that pre-mRNA formed clouds around the transcription site. These clouds indicate the existence of a transcription-site-proximal zone through which RNA move more slowly than in the nucleoplasm. Full-length pre-mRNA undergo continuous splicing as they move through this zone following transcription, suggesting a model in which splicing can occur post-transcriptionally but still within the proximity of the transcription site, thus seeming co-transcriptional by most assays. These results may unify conflicting reports of co-transcriptional versus post-transcriptional splicing.
剪接是一个逐步的分子过程，通过该过程，内含子从前体 mRNA 中被去除，外显子连接在一起形成成熟的 mRNA 序列。这些步骤的顺序和空间分布仍然存在争议，对立的模型表明剪接要么发生在转录过程中，要么发生在转录之后。我们使用单分子 RNA FISH、扩展显微镜和活细胞成像来揭示哺乳动物细胞中新生转录物的时空分布。在超分辨率水平上，我们发现前体 mRNA 在转录位点周围形成云。这些云表明存在一个转录位点近端区域，其中 RNA 的移动速度比核质中慢。全长前体 mRNA 在转录后通过该区域移动时会不断进行剪接，这表明剪接可以在转录后发生，但仍然靠近转录位点，因此在大多数测定中似乎是共转录的。这些结果可能会统一关于共转录与转录后剪接的相互矛盾的报告。
