Histone monoaminylation dynamics are regulated by a single enzyme and promote neural rhythmicity

Histone H3 monoaminylations at glutamine(Q) 5 represent important epigenetic markers in neurons that play critical roles in the mediation of permissive gene expression. We previously demonstrated that H3Q5 serotonylation(ser) and dopaminylation(dop) are catalyzed by the Transglutaminase 2 (TGM2) enzyme. Here, we identified a new class of histone monoaminylation, H3Q5 histaminylation(his), which displayed dynamic diurnal expression in brain and contributed to neural rhythmicity. We found that H3Q5his, unlike H3Q5ser, electrostatically inhibited recruitment of the “reader” protein WDR5 and attenuated MLL1 methyltransferase activity on H3 lysine(K) 4. We determined that H3Q5 monoaminylation dynamics are dictated by local monoamine concentrations, which are sensed by TGM2. This noncanonical mechanism indicated that histone monoaminylations can be established and removed by a single enzyme based upon its sensing of cellular microenvironments. Overall design: Brain tissue was collected every 4 h across the 24 h zeitgeber, 21 d post viral-infusion, or following behavioral assays. For viral infused brains, Adeno-associated virus H3.3 constructs [empty vs. wildtype (WT) vs. (Q5A)- Flag-HA] were used - all three containing an IRES driven GFP fluorescent tag to allow visualization of the injection site during tissue dissection. Animals were anaesthetized with isoflurane (1-3%) and positioned in a stereotaxic frame (Kopf instruments) and 0.5 µl of viral construct was infused bilaterally into TMN using the following coordinates; anterior-posterior (AP) -2.3, medial-lateral (ML) +1.0, dorsal-ventral (DV) -5.5. All brains were immediately frozen following collection. For zeitgeber brains, tissues were sectioned at 1 mm thick and TMN was collected by tissue punch (1-2 mm). For virus-infused brains, tissue was sectioned at 150 µm on a cryostat, and GFP was illuminated using a NIGHTSEA BlueStar flashlight to microdissect virally infected tissues.