Co-transcriptional splicing, once viewed primarily as a routine step in messenger RNA production, is emerging as a central regulator of gene expression, genome stability and disease biology. A new review in Science Bulletin presents a systematic framework that connects the detection, measurement, regulation, molecular functions and therapeutic potential of this process. The authors argue that understanding when and how introns are removed while RNA is still being synthesized could reshape how scientists interpret communication between transcription, RNA processing, chromatin and protein production.
Unlike conventional models in which RNA is transcribed first and spliced later, co-transcriptional splicing occurs directly on nascent RNA as RNA polymerase II moves along a gene. The spliceosome, a large and dynamic molecular machine, recognizes splice sites and assembles on the emerging transcript before transcription has finished. This timing creates opportunities for transcription and splicing to influence one another, allowing the cell to adjust RNA maturation according to polymerase speed, chromatin organization, RNA structure and the availability of regulatory proteins.
The review divides current detection technologies into imaging-based methods and high-throughput sequencing approaches. Imaging can reveal splicing events in living cells or at the single-molecule level, offering information about where and when individual transcripts are processed. Sequencing-based techniques, meanwhile, can examine nascent RNA across the genome, enabling researchers to map splicing behavior at thousands of genes simultaneously. Together, these approaches are helping scientists move beyond static measurements and reconstruct splicing as a dynamic process unfolding in real time.
Three quantitative concepts are especially important: splicing time, splicing order and splicing efficiency. Splicing time describes how rapidly a particular intron is removed after it becomes available to the spliceosome. Splicing order identifies which introns are processed first when a transcript contains multiple introns, while splicing efficiency measures the proportion of transcripts that undergo successful removal. These metrics can expose hidden patterns in gene regulation, including cases in which the order of intron removal changes the eventual protein products or determines whether an RNA is retained, degraded or exported from the nucleus.
According to the review, the regulation of co-transcriptional splicing can be organized around two broad questions: how accessible is the splice substrate, and how effectively can the splicing machinery assemble? Accessibility is shaped partly by the speed of RNA polymerase II. A rapidly moving polymerase may reduce the time available for splice-site recognition, whereas slower elongation can provide a wider window for spliceosome assembly. Chromatin modifications, nucleosome positioning, the folding of nascent RNA and chemical RNA modifications can further expose or conceal splice sites, influencing which processing decisions are made.
The second regulatory layer concerns the composition and organization of the spliceosome and its surrounding environment. RNA polymerase II can recruit or stabilize splicing factors as transcription proceeds, while chromatin adaptors help coordinate transcription with RNA processing. RNA-binding proteins may guide splice-site selection, and chemical modifications of splicing factors can alter their activity, localization or interactions. The spatial organization of the nucleus also matters: transcription sites, nuclear speckles and other compartments can concentrate particular factors, bringing nascent transcripts into contact with the machinery needed for rapid processing.
The consequences extend far beyond the production of mature messenger RNA. Co-transcriptional splicing can influence chromatin structure and help prevent the formation of R-loops, unusual structures made of RNA hybridized to DNA with a displaced single DNA strand. Excessive R-loop accumulation can interfere with replication and transcription, increasing the risk of DNA damage and genome instability. Splicing also intersects with RNA editing, RNA modification, nuclear retention, degradation and translation. By influencing which RNA isoforms survive and reach ribosomes, the process can ultimately expand or restrict the diversity of proteins produced by a cell.
These connections make co-transcriptional splicing relevant to a broad range of diseases. The review links its dysregulation to blood disorders, cancer and neurological disease. Mutations may alter the recognition of splice sites, weaken spliceosome assembly or disturb feedback between splicing, transcription and chromatin. The resulting errors can change RNA fate, generate abnormal protein isoforms, promote genomic instability or disrupt the specialized gene-expression programs required for cell survival. In cancer, for example, abnormal splicing can support uncontrolled growth, while in neurological disorders even modest changes in RNA processing may affect long-lived and highly specialized cells.
The emerging picture also suggests therapeutic possibilities that extend beyond directly correcting faulty RNA sequences. Antisense oligonucleotides could redirect splice-site recognition, while small molecules might modify spliceosome activity or alter the accessibility of specific RNA regions. Drugs targeting chromatin states could change the transcriptional environment in which splicing occurs, and treatments designed to reduce harmful R-loop accumulation might protect genome stability. Combining these approaches with existing epigenetic or precision-medicine strategies could eventually provide ways to correct the broader regulatory environment surrounding aberrant splicing rather than treating a single RNA error in isolation.
The authors emphasize that the field remains young, with important mechanisms still under debate and clinical applications at an early stage. Future progress is expected from the integration of live-cell imaging, long-read sequencing, single-cell analysis and spatial omics. These technologies could reveal how splicing decisions vary between individual cells, tissues and disease states, while also clarifying how the timing of intron removal influences protein output. By placing co-transcriptional splicing at the intersection of transcription, chromatin regulation and RNA fate, the review identifies it as a promising frontier for both fundamental biology and therapeutic innovation.
Subject of Research: Co-transcriptional RNA splicing, its detection, regulation, molecular functions, disease associations and therapeutic implications.
News Publication Date: Not provided.
Web References: https://doi.org/10.1016/j.scib.2026.07.025
References: Science Bulletin, DOI: 10.1016/j.scib.2026.07.025
Image Credits: © Science Bulletin
Keywords: Co-transcriptional splicing, RNA processing, spliceosome, RNA polymerase II, nascent RNA, chromatin regulation, R-loops, gene expression, cancer, neurological disease, antisense oligonucleotides, RNA therapeutics
