Stoichiometric m6A regulation of YY1 orchestrates the metabolic switch during cardiac development

Chemical modifications of RNA provide an additional regulatory layer essential for development. N6-methyladenosine (m6A) is the most abundant internal mRNA mark, but how site specificity, stoichiometry, and cellular context together determine mRNA fate remains unclear. Here, we define these rules in cardiogenesis by combining single-molecule nanopore direct RNA sequencing (DRS) with a CRISPR-dCas13 epitranscriptomic editing platform in human induced pluripotent stem cells and a conditional Mettl14 cardiac knockout in mice, integrated with multi-omics, to map m6A sites and quantify stoichiometry. We uncover a bimodal m6A code in which low versus high modification ratios are associated with opposite mRNA and protein outcomes. We further show that Mettl14 loss causes developmental cardiomyopathy and embryonic lethality by disrupting the glycolysis-to-oxidative phosphorylation (OXPHOS) metabolic switch, and identify an m6A-YY1 (Yin Yang 1) axis that post-transcriptionally controls OXPHOS genes. Finally, targeted installation of m6A at defined sites using CRISPR-dCas13 reveals that m6A effects on YY1 are strongly locus- and context-dependent. Together, these findings establish m6A as a site- and stoichiometry-dependent regulatory code interpreted by cellular context to direct cardiac metabolic maturation. These principles are likely to extend to other developmental and physiological contexts in which precise control of metabolic state and gene dosage is required.