A study in Molecular Cell introduces SLAM-RT&Tag, a method that combines in situ transcript mapping with metabolic RNA labeling to track the location and timing of RNA processing inside the nucleus.
The researchers focused on two major nuclear compartments: Polycomb domains and nuclear speckles.
Using antibodies against H3K27me3 and SC35, they tethered a reverse transcriptase and Tn5 transposase to specific chromatin regions or speckle components. This enabled the sequencing of transcripts that are spatially linked to each compartment. By adding 4-thiouridine (s4U) labeling and quantifying T>C transitions, SLAM-RT&Tag allowed them to estimate RNA half-lives locally and globally.
In Polycomb-marked regions, they found that transcripts didn’t originate within the domains themselves but from unusually long genes positioned nearby. These transcripts often contained unspliced introns, suggesting they were nascent. Most had short chromatin-localized half-lives, indicating they moved away from Polycomb domains shortly after transcription. Only a few, like XIST, persisted.
In contrast, nuclear speckles were enriched with polyadenylated transcripts that still contained introns. These transcripts typically originated elsewhere and migrated into speckles, possibly for splicing. The majority were transient, with residence times of about 2–4 hours. Splicing inhibition increased transcript accumulation in speckles, supporting their role as post-transcriptional splicing sites. A minority, including MALAT1, showed prolonged association.
By comparing localized and global RNA dynamics, the team concluded that compartmentalization within the nucleus supports different modes of RNA maturation. Polycomb domains appear to act as spatial buffers for long transcription units, while speckles serve as transient processing hubs for partially spliced RNAs.
Publication Details:
Khyzha, N., Ahmad, K., & Henikoff, S. (2025). Profiling transcriptome composition and dynamics within nuclear compartments using SLAM-RT&Tag. Molecular cell, 85(7), 1366-1380. DOI: 10.1016/j.molcel.2025.02.012
The researchers focused on two major nuclear compartments: Polycomb domains and nuclear speckles.
Using antibodies against H3K27me3 and SC35, they tethered a reverse transcriptase and Tn5 transposase to specific chromatin regions or speckle components. This enabled the sequencing of transcripts that are spatially linked to each compartment. By adding 4-thiouridine (s4U) labeling and quantifying T>C transitions, SLAM-RT&Tag allowed them to estimate RNA half-lives locally and globally.
In Polycomb-marked regions, they found that transcripts didn’t originate within the domains themselves but from unusually long genes positioned nearby. These transcripts often contained unspliced introns, suggesting they were nascent. Most had short chromatin-localized half-lives, indicating they moved away from Polycomb domains shortly after transcription. Only a few, like XIST, persisted.
In contrast, nuclear speckles were enriched with polyadenylated transcripts that still contained introns. These transcripts typically originated elsewhere and migrated into speckles, possibly for splicing. The majority were transient, with residence times of about 2–4 hours. Splicing inhibition increased transcript accumulation in speckles, supporting their role as post-transcriptional splicing sites. A minority, including MALAT1, showed prolonged association.
By comparing localized and global RNA dynamics, the team concluded that compartmentalization within the nucleus supports different modes of RNA maturation. Polycomb domains appear to act as spatial buffers for long transcription units, while speckles serve as transient processing hubs for partially spliced RNAs.
Publication Details:
Khyzha, N., Ahmad, K., & Henikoff, S. (2025). Profiling transcriptome composition and dynamics within nuclear compartments using SLAM-RT&Tag. Molecular cell, 85(7), 1366-1380. DOI: 10.1016/j.molcel.2025.02.012
