PROJECT SUMMARY Monoaminergic systems in the brain play critical roles in the regulation of a wide variety of neural processes, and are heavily implicated in the etiology of numerous mood-related disorders in humans, including major depressive disorder (MDD). While mood disorders are highly heritable, it is clear that environmental factors also contribute significantly to disease, with chronic stress representing one of the most common precipitating factors for mood-related diagnoses. In recent years, persistent stress-induced alterations in gene expression have been demonstrated to promote physiological alterations implicated in mood disorders, and more recently, histone mechanisms affecting cell-type and regional specific chromatin structures have been causally linked to the regulation of transcriptional programs that contribute to stress-mediated behaviors in preclinical rodent models, as well as their responses to antidepressants (ADs). However, our understanding of how these mechanisms mediate neural dysfunction in response to stress remains limited, and mechanistic connections between altered monoaminergic signaling and resulting chromatin regulatory phenomena have remained elusive. Our lab recently identified and mechanistically characterized histone proteins as novel substrates for so- called monoaminylation in brain, a novel class of post-translational modification that contributes significantly to gene expression in the central nervous system. In addition, we have observed that H3 monoaminylation states are perturbed in postmortem brains of individuals diagnosed with certain psychiatric disorders related to monoaminergic dysfunction (e.g., MDD), as well as in brains of pre-clinical rodent models for the study of these disorders, phenomena that contribute importantly to transcriptional, physiological and behavioral deficits in these models. We have also recently identified the protein NQO2 as the bona fide “reader” of H3 serotonylation (H3Q5ser) in vivo. Since our previous data indicated aberrant roles for H3Q5ser accumulation in brain of chronically stressed male and female mice as an important contributor to stress-mediated transcriptional and behavioral plasticity (an effect completely reversed by chronic fluoxetine treatments), we now hypothesize that NQO2 recruitment to loci displaying elevated H3Q5ser enrichment in response to stress may contribute importantly to transcriptional programs that result in persistent stress susceptibility. These phenomena, when attenuated by blockade of NQO2’s ability to bind to H3Q5ser, may then result in therapeutic outcomes, and may further help to explain the mechanistic actions of traditional ADs. Here, we thus aim to: (1) mechanistically characterize NQO2’s biochemical/molecular impact on H3Q5ser function in vitro (within a nucleosomal context) and in cells; (2) rigorously characterize the cell-type specific impact of NQO2-H3Q5ser interactions on stress- mediated transcriptional and behavioral pl...