Understanding the many layers of RNA biology is key to unraveling how our genes are regulated, especially as we age. A recent paper by researchers at the Chinese Academy of Sciences, introduces a powerful new tool called CompasSeq that does just that. This analytical platform offers a novel way to examine and quantify special chemical caps found at the beginning of RNA molecules, specifically, those initiated by nucleotide-containing metabolites like NAD, rather than the more common m7G cap.

The workflow of CompasSeq

a CompasSeq implements a parallel experimental pipeline to simultaneously capture NCIN-capped RNAs and all-capped RNAs (NCIN- and m⁷G-capped RNAs). Meanwhile, CompasSeq implements a dual spike-in strategy to quantify NCIN-capped RNAs. A set of synthetic NCIN-RNAs with known capping ratios, is introduced at the beginning to serve as internal controls. Adapter-pre-ligated Drosophila RNA, is added at the step of cDNA library construction for subsequent computational analysis. b Diagram illustrating the workflow of CompassAnalyzer. CompassAnalyzer first applies stepwise normalizations to recover the intrinsic RNA abundance distribution between NCIN-capped and all-capped RNAs from sequencing data. It then employs empirical Bayes shrinkage to enable quantification of NCIN capping ratios at the transcript level.

These noncanonical caps (NCIN caps) are not just oddities. They may influence how RNA molecules function and how cells respond to stress, aging, or disease. Until now, scientists could only detect specific types of these caps in limited contexts. CompasSeq changes that by providing an epitranscriptome-wide approach. It combines precise lab techniques with sophisticated computational analysis to measure how many RNAs carry these special caps and how this varies across different genes.

To ensure the results are accurate, the researchers also developed a backup method called the “quantitative exoribonuclease reduction assay.” Using these tools, they studied RNA from mouse liver and found that the percentage of NCIN-capped RNAs changes with age. Interestingly, the amount of RNA produced by certain genes didn’t always match how often their RNAs were NCIN-capped, especially for genes related to aging.

This work opens the door to deeper functional studies of NCIN-capped RNAs and suggests they may play a bigger role in gene regulation than previously thought. CompasSeq could be a game-changer for scientists exploring the complex world of RNA modifications.

Availability – CompassAnalyzer is available as an R package on GitHub (https://github.com/thereallda/compassanalyzer)