METTL3 Uncouples Chromatin Accessibility from Transcription during Retinal Development

METTL3 is a key regulator of RNA metabolism, yet its genomic and epitranscriptomic roles in tissue development are largely unexplored. Using embryonic stem cell-derived 3D retinal organoids to model retinal progenitor cell (RPC) differentiation, we integrated transcriptome-wide m6A profiling (GLORI), protein-DNA (ChIP-seq and CUT&RUN) and chromatin accessibility (ATAC-seq) mapping, and targeted m6A engineering (dCas13b-FTO) to dissect METTL3 function. Loss of METTL3 nuclear m6A activity disrupted Rx+ retinal anlage formation in vitro, with dCas13b-FTO epitranscriptome engineering revealing that m6A at the Six3 3UTR governs its stability. Surprisingly, while METTL3 loss altered histone modifications and chromatin accessibility, its direct chromatin targets showed little transcriptional correlation. A degron-based METTL3 degradation strategy, paired with protein-RNA interaction profiling, exposed rapid regulatory shifts in RPCs, revealing a METTL3-Ythdf1 protein-RNA axis. Our multi-omics approach establishes METTL3-dependent m6A as a critical epitranscriptomic layer in retinal development, unveiling a genomic paradigm in which chromatin accessibility diverges from transcriptional output.