The mRNA methyltransferase Mettl3 modulates cytokine mRNA stability and limits functional responses in mast cells

Mast cells are central players in allergy and asthma, and their dysregulated responses lead to reduced quality of life and life-threatening conditions such as anaphylaxis. The RNA modification N 6 -methyladenosine (m 6 A) has a prominent impact on immune cell functions, but its role in mast cells remains unexplored. Here, by optimizing tools to genetically manipulate primary mast cells, we reveal that the m 6 A mRNA methyltransferase complex modulates mast cell proliferation and survival. Depletion of the catalytic component Mettl3 exacerbates effector functions in response to IgE and antigen complexes, both in vitro and in vivo. Mechanistically, deletion of Mettl3 or Mettl14, another component of the methyltransferase complex, lead to the enhanced expression of inflammatory cytokines. By focusing on one of the most affected mRNAs, namely the one encoding the cytokine IL-13, we find that it is methylated in activated mast cells, and that Mettl3 affects its transcript stability in an enzymatic activity-dependent manner, requiring consensus m 6 A sites in the Il13 3’-untranslated region. Overall, we reveal that the m 6 A machinery is essential in mast cells to sustain growth and to restrain inflammatory responses. The m 6 A mRNA modification is essential for immune cell function. Here, the Monticelli lab optimized methods of gene editing by CRISPR-Cas9 in mast cells and revealed how the m 6 A machinery is required to sustain proliferation and to limit the production of inflammatory cytokines by these cells.