Glutamine 5 serotonylation on histone H3 is a permissive modification that functions combinatorialy with H3K4me3 to potentiate TFIID interactions

Chemical modifications of histone proteins, along with the ?writers,? ?erasers? and ?readers? of these modifications, are capable of mediating a diverse set of DNA-templated processes including gene transcription1-7. Here, we provide evidence for a new class of histone posttranslational modification (PTM), serotonylation of glutamine, which occurs at position 5 (Q5ser) on histone H3 in serotonin (5-hydroxytryptamine, 5-HT) producing organisms. We demonstrate that the tissue Transglutaminase 2 (TGM2) enzyme, a transamidase that is both necessary and sufficient to deposit the mark, can serotonylate H3 on lysine 4 tri-methylated (H3K4me3) nucleosomes resulting in the presence of combinatorial H3K4me3Q5ser in vivo. H3K4me3Q5ser displays a ubiquitous pattern of tissue expression in mammals, with predicted enrichment observed in brain and gut, two organ systems responsible for the bulk of 5-HT production. Genome-wide analyses of its enrichment in human serotonergic neurons, developing mouse brain and cultured serotonergic cells, using an H3K4me3Q5ser specific antibody, indicate that the mark is enriched in euchromatin, is sensitive to cellular differentiation and correlates with permissive gene expression, phenomena that are linked to the mark?s potentiation of TFIID8-10 interactions with H3K4me3. Cells ectopically expressing an H3 mutant that cannot be serotonylated display significantly altered expression of H3K4me3Q5ser target loci leading to deficits in differentiation. Taken together, these data identify a direct role for 5-HT, independent from its contributions to neurotransmission and cellular signaling, in the mediation of permissive gene expression in mammalian cells, and further define its biophysical activities as a putative co-regulator of TFIID recruitment to H3K4me3 marked chromatin. Investigation of H3K4me3 and H3K4me3Q5ser marks in RN46A-B14 cells; Investigation of associations of H3K4me3 and H3K4me3Q5ser marks with gene expression and TAF3 recruitment to chromatin in RN46A-B14 cells; Investigation of H3K4me3 and H3K4me3Q5ser marks in embryonic rodent brain; Investigation of associations of H3K4me3 and H3K4me3Q5ser marks with gene expression in embryonic rodent brain; Investigation of the H3K4me3Q5ser marks in human PSCs vs. 5-HT neurons; investigation of associations of H3K4me3Q5ser in human PSCs vs. 5-HT neurons with gene expression.