Title: Landscape and Regulation of m⁶A and m⁶Am Methylome across Human and Mouse Tissues

Abstract: N⁶-methyladenosine (m⁶A), the most abundant internal mRNA modification, and N⁶,2′-O-dimethyladenosine (m⁶Am), found at the first-transcribed nucleotide, are two reversible epitranscriptomic marks. However, the profiles and distribution patterns of m⁶A and m⁶Am across human and mouse tissues are poorly characterized. Here, we report the m⁶A and m⁶Am methylome through profiling of 43 human and 16 mouse tissues and demonstrate strongest tissue specificity for the brain tissues. A small subset of tissue-specific m⁶A peaks can also readily classify tissue types. The overall m⁶A and m⁶Am level is partially correlated with the expression level of their writers and erasers. Additionally, the m⁶A-containing regions are enriched for SNPs. Furthermore, cross-species analysis revealed that species rather than tissue type is the primary determinant of methylation. Collectively, our study provides an in-depth resource for dissecting the landscape and regulation of the m⁶A and m⁶Am epitranscriptomic marks across mammalian tissues.