Role of m6A RNA methylation in dosage compensation

In therian mammals, inactivation of one of the X-chromosomes in female cells (XX) balances the dosage of X-linked gene expression between the sexes, resulting in monoallelic expression of X-linked genes in females similar to males (XY). Therefore, it creates a dosage imbalance for X-linked genes with respect to the biallelically expressing autosomal genes (AA). X-to-autosome dosage compensation is thought to be achieved by the transcriptional upregulation of many genes from the active X-chromosome in both sexes. Here, we have delineated the role of m6A RNA methylation in the maintenance of dosage compensation in a variety of cell types, including embryonic, extra-embryonic and somatic cells. We show that m6A marks tend to be less enriched on X-linked transcripts compared to the autosomal transcripts in most of the studied cell types. However, our analysis demonstrates that m6A RNA methylation plays a minor role in dosage compensation. We show that the loss of m6A RNA methylation does not affect the maintenance of X-linked gene silencing on the inactive-X in early embryonic lineages, suggesting m6A is dispensable for the maintenance of X-chromosome inactivation. On the contrary, we show that the depletion of m6A affects X-to-autosome dosage compensation, however, the effect is minor and it occurs in a lineage-specific manner. Taken together, our study demonstrates that, although m6A marks are lowly enriched on X-linked transcripts compared to autosomal ones, it is dispensable for the maintenance of X-inactivation and has a minor contribution to the maintenance of X-to-autosome dosage compensation.