RNA stability controlled by m6A methylation provides X to autosome compensation in mammals [SLAM-seq]

In therian mammals, X-chromosomal genes are expressed only from a single active X chromosome, both in males (XY) as well as females (XX). To compensate for this reduction in dosage compared to the evolutionary ancestral state on two autosomes, it has been proposed that genes from the active X chromosome exhibit dosage compensation (“Ohno's hypothesis”). However, the existence and mechanism of X-to-autosome dosage compensation are still under debate. Here, we show that dosage compensation is achieved via differential N6-methyladenosine (m6A) RNA modification. X-chromosomal transcripts are reduced in m6A modifications and more stable compared to the autosomal counterparts. Acute depletion of m6A using a small molecule inhibitor differentially affects autosomal and X-chromosomal transcripts across sexes, cell types, tissues and species, resulting in perturbed dosage compensation. We propose that higher stability of X-chromosomal transcripts is directed by lower levels of m6A, indicating that mammalian dosage compensation occurs via epitranscriptomic RNA regulation. Overall design: SLAMseq experiment was performed for total RNA of male mES cells in 4 replicates per condition.