FOCAS: Transcriptome-wide screening of individual m6A sites functionally dissects epitranscriptomic control of gene expression in cancer [FOCAS_GLORI]

Although N6-methyladenosine (m6A) is a pervasive RNA modification essential for gene regulation, dissecting the functions of individual m6A sites remains technically challenging. To overcome this, we developed functional m6A sites detection by CRISPR-dCas13b-FTO screening (FOCAS), a CRISPR-dCas13b-based platform enabling high-throughput, site-specific functional screening of m6A. Applying FOCAS to four human cancer cell lines identified 4,475 m6A-regulated genes influencing cell fitness via both mRNAs and non-coding RNAs (ncRNAs), many of which are newly linked to cancer and exhibit dynamic developmental expression. FOCAS uncovered context-dependent and reader-specific effects of m6A within the same gene, revealing its intricate regulatory logic. We further uncovered universal and cell-type-specific m6A patterns with unique sites enriched in ncRNAs and universal ones in transcription-related genes. In SMMC-7721 cells we identified m6A-regulated transcriptional networks that demonstrated extensive epitranscriptome-transcriptome crosstalk. Overall, this study established a powerful, unbiased approach for the functional dissection of m6A, advancing the understanding of its complexity and therapeutic relevance in cancers. Overall design: We detected the modification levels of m6A sites in SMMC-7721-dCas13b-wtFTO cells, HepG2-dCas13b-wtFTO cells, HCT116-dCas13b-wtFTO cells and HeLa-dCas13b-wtFTO cells treated with sgRNAs.