RNA "delivery tags" guide key messages to distant neuron branches. A research team from Korea Advanced Institute of Science and Technology (KAIST) has uncovered how a small chemical modification on RNA acts like a "delivery tag," enabling specific RNAs to travel to faraway regions of neurons. This discovery could help scientists investigate "delivery errors" in brain disorders, where RNA is made correctly but doesn't reach its intended location, potentially leading to new treatments. The study, led by Professor Ki-Jun Yoon from the Department of Biological Sciences, was published in the journal Nature Communications and focuses on a modification called N6-methyladenosine, or m6A, which helps transport specific RNAs to the ends of neurons' long, cable-like projections called axons. Neurons are unique in that they have long, branched structures. Axons send signals to other neurons, while dendrites receive them. For the brain to develop and function properly, these structures need to grow and connect correctly. Since neurons can be very long, RNA produced in the cell body often needs to travel to distant parts, such as the tip of an axon. This means neurons must identify the right RNAs among thousands and transport them precisely. However, the mechanisms behind this process have been poorly understood until now. The research team found that m6A, a chemical modification on RNA, plays a key role in this transport. m6A is a small change to adenosine, one of the building blocks of RNA, and is known to affect RNA stability and protein production. The new study shows that m6A also acts as a molecular "delivery tag" that helps guide specific RNAs to distant parts of neurons. To test this, the researchers studied mice with a gene called Mettl14 deleted, which is involved in adding m6A to RNA. Without this modification, neurons had trouble forming axons and other extensions, confirming m6A's role in early brain development. The team also mapped the precise locations of m6A modifications in the developing mouse brain using a high-resolution technique called m6A-SAC-seq. This detailed map showed that RNAs involved in axon growth and synapse formation were marked with m6A. The researchers identified how this tag is recognized and used by the cell. A protein called YTHDF2, which normally helps degrade RNA, was found to work with other proteins—FMRP and KIF5C—to transport RNA along neurons. This process is similar to a delivery system, where m6A is the tag, YTHDF2 reads it, and the other proteins help move the RNA to its destination. These findings offer a new way to think about brain disorders. While past research focused on whether RNA is made correctly, this study suggests that researchers should also consider whether RNA is delivered properly within neurons. Problems with RNA delivery, rather than the RNA itself, might contribute to neurological diseases. Future studies could explore whether such errors occur in conditions like autism or Alzheimer's and whether they lead to disease. The detailed m6A map generated in this study could also help scientists understand how RNA modifications change during aging and disease. Professor Yoon hopes these findings will lead to a better understanding of RNA delivery failures in the brain and open the door to new therapeutic strategies.