The m⁶A reader YTHDF2 regulates mRNA transport and axon outgrowth in developing neurons.

Proper nervous system development is critical for brain function, and deficits in neural development are implicated in many brain disorders. Neurons are distinctly polarized cells where mRNA can be transported to distal structures like axons and dendrites. Recent discoveries of widespread mRNA chemical modifications raise the question of their post-transcriptional regulatory role in brain development and function. N6-methyladenosine (m6A), installed by the METTL3/METTL14 methyltransferase complex, is the most prevalent internal mRNA modification, influencing stability, translation, splicing, and localization. However, the impact of m6A modification on RNA transport in developing neurons is not well understood. In this study, we find that the ablation of Mettl14 in postmitotic neurons leads to impaired axonal projection during corticogenesis. RNA-seq and single-molecule in situ hybridization reveal mislocalization of mRNAs in neurites of neurons with m6A loss-of-function. Furthermore, m6A-SAC-seq to identify a single nucleotide resolution m6A maps in the perinatal brain uncovers m6A-tagged transcripts associated with synapse organization, mRNA processing, and axonogenesis. We also identify YTHDF2 as the reader protein responsible for mRNA transport in callosal projection axons. YTHDF2 interacts with motor proteins, translational regulators, and microtubules to facilitate distal transport of m6A-tagged mRNA. Our data suggest that FMRP may serve as a context-guiding interactor that reshapes the YTHDF2 complex by recruiting specific cofactors and motor proteins, thereby promoting transport rather than degradation of m⁶A-tagged transcripts. Together, these findings provide insight into the epitranscriptomic mechanisms governing axon projection and guidance during mammalian cortical neurogenesis.