Stress-induced transcriptional readthrough into neighboring genes is linked to intron retention

Exposure to certain stresses leads to readthrough transcription. Here we found that readthrough transcription often proceeds into the proximal gene downstream, in a phenomenon termed "read-in". Using polyA-selected RNA-seq data from mouse fibroblasts, we identified widespread read-in in heat shock, oxidative and osmotic stress conditions. We found that read-in genes share distinctive genomic characteristics; they are extremely short, and highly GC rich. Furthermore, using ribosome footprint profiling we found that translation of read-in genes is significantly reduced. Strikingly, read-in genes show extremely high levels of intron retention during stress, mostly in their first intron, which is not explained by features usually associated with intron retention, such as short introns and high GC content. Finally, we found that first introns in read-in genes have weaker splice sites. Our data portray a relationship between read-in and intron retention, suggesting it may have co-evolved to facilitate reduced translation of read-in genes during stress.