Sperm transcriptional state associated with paternal transmission of stress phenotypes.

Paternal stress can induce long-lasting changes in germ cells potentially propagating heritable changes across generations. To date, no studies have investigated differences in transmission patterns between stress-resilient and -susceptible mice. We tested the hypothesis that transcriptional alterations in sperm during chronic social defeat stress (CSDS) transmit increased susceptibility to stress phenotypes to the next generation. We demonstrate differences in offspring from stressed fathers that depend upon paternal category (resilient vs susceptible) and offspring sex. Importantly, artificial insemination reveals that sperm mediates some of the behavioral phenotypes seen in offspring. Using RNA-sequencing we report substantial and distinct changes in the transcriptomic profiles of sperm following CSDS in susceptible vs resilient fathers, with alterations in long noncoding RNAs (lncRNAs) predominating especially in susceptibility. Correlation analysis revealed that these alterations were accompanied by a loss of regulation of protein-coding genes by lncRNAs in sperm of susceptible males. We also identify several co-expression gene modules that are enriched in differentially expressed genes in sperm from either resilient or susceptible fathers. Taken together, these studies advance our understanding of intergenerational epigenetic transmission of behavioral experience.SIGNIFICANCE STATEMENTThis manuscript contributes to the complex factors that influence the paternal transmission of stress phenotypes. By leveraging the segregation of males exposed to chronic social defeat stress into either resilient or susceptible categories we were able to identify the phenotypic differences in the paternal transmission of stress phenotypes across generations between the two lineages. Importantly, this work also alludes to the significance of both long noncoding RNAs and protein coding genes mediating the paternal transmission of stress. The knowledge gained from these data is of particular interest in understanding the risk for the development of psychiatric disorders such as anxiety and depression.

Aberrant H3.3 dynamics in NAc promote vulnerability to depressive-like behavior.

Human major depressive disorder (MDD), along with related mood disorders, is among the world's greatest public health concerns; however, its pathophysiology remains poorly understood. Persistent changes in gene expression are known to promote physiological aberrations implicated in MDD. More recently, histone mechanisms affecting cell type- and regional-specific chromatin structures have also been shown to contribute to transcriptional programs related to depressive behaviors, as well as responses to antidepressants. Although much emphasis has been placed in recent years on roles for histone posttranslational modifications and chromatin-remodeling events in the etiology of MDD, it has become increasingly clear that replication-independent histone variants (e.g., H3.3), which differ in primary amino acid sequence from their canonical counterparts, similarly play critical roles in the regulation of activity-dependent neuronal transcription, synaptic connectivity, and behavioral plasticity. Here, we demonstrate a role for increased H3.3 dynamics in the nucleus accumbens (NAc)-a key limbic brain reward region-in the regulation of aberrant social stress-mediated gene expression and the precipitation of depressive-like behaviors in mice. We find that molecular blockade of these dynamics promotes resilience to chronic social stress and results in a partial renormalization of stress-associated transcriptional patterns in the NAc. In sum, our findings establish H3.3 dynamics as a critical, and previously undocumented, regulator of mood and suggest that future therapies aimed at modulating striatal histone dynamics may potentiate beneficial behavioral adaptations to negative emotional stimuli.

In vivo imaging identifies temporal signature of D1 and D2 medium spiny neurons in cocaine reward.

The reinforcing and rewarding properties of cocaine are attributed to its ability to increase dopaminergic transmission in nucleus accumbens (NAc). This action reinforces drug taking and seeking and leads to potent and long-lasting associations between the rewarding effects of the drug and the cues associated with its availability. The inability to extinguish these associations is a key factor contributing to relapse. Dopamine produces these effects by controlling the activity of two subpopulations of NAc medium spiny neurons (MSNs) that are defined by their predominant expression of either dopamine D1 or D2 receptors. Previous work has demonstrated that optogenetically stimulating D1 MSNs promotes reward, whereas stimulating D2 MSNs produces aversion. However, we still lack a clear understanding of how the endogenous activity of these cell types is affected by cocaine and encodes information that drives drug-associated behaviors. Using fiber photometry calcium imaging we define D1 MSNs as the specific population of cells in NAc that encodes information about drug associations and elucidate the temporal profile with which D1 activity is increased to drive drug seeking in response to contextual cues. Chronic cocaine exposure dysregulates these D1 signals to both prevent extinction and facilitate reinstatement of drug seeking to drive relapse. Directly manipulating these D1 signals using designer receptors exclusively activated by designer drugs prevents contextual associations. Together, these data elucidate the responses of D1- and D2-type MSNs in NAc to acute cocaine and during the formation of context-reward associations and define how prior cocaine exposure selectively dysregulates D1 signaling to drive relapse.

Histone arginine methylation in cocaine action in the nucleus accumbens.

Repeated cocaine exposure regulates transcriptional regulation within the nucleus accumbens (NAc), and epigenetic mechanisms-such as histone acetylation and methylation on Lys residues-have been linked to these lasting actions of cocaine. In contrast to Lys methylation, the role of histone Arg (R) methylation remains underexplored in addiction models. Here we show that protein-R-methyltransferase-6 (PRMT6) and its associated histone mark, asymmetric dimethylation of R2 on histone H3 (H3R2me2a), are decreased in the NAc of mice and rats after repeated cocaine exposure, including self-administration, and in the NAc of cocaine-addicted humans. Such PRMT6 down-regulation occurs selectively in NAc medium spiny neurons (MSNs) expressing dopamine D2 receptors (D2-MSNs), with opposite regulation occurring in D1-MSNs, and serves to protect against cocaine-induced addictive-like behavioral abnormalities. Using ChIP-seq, we identified Src kinase signaling inhibitor 1 (Srcin1; also referred to as p140Cap) as a key gene target for reduced H3R2me2a binding, and found that consequent Srcin1 induction in the NAc decreases Src signaling, cocaine reward, and the motivation to self-administer cocaine. Taken together, these findings suggest that suppression of Src signaling in NAc D2-MSNs, via PRMT6 and H3R2me2a down-regulation, functions as a homeostatic brake to restrain cocaine action, and provide novel candidates for the development of treatments for cocaine addiction.

Targeted Epigenetic Remodeling of the Cdk5 Gene in Nucleus Accumbens Regulates Cocaine- and Stress-Evoked Behavior.

UNLABELLED: Recent studies have implicated epigenetic remodeling in brain reward regions following psychostimulant or stress exposure. It has only recently become possible to target a given type of epigenetic remodeling to a single gene of interest, and to probe the functional relevance of such regulation to neuropsychiatric disease. We sought to examine the role of histone modifications at the murine Cdk5 (cyclin-dependent kinase 5) locus, given growing evidence of Cdk5 expression in nucleus accumbens (NAc) influencing reward-related behaviors. Viral-mediated delivery of engineered zinc finger proteins (ZFP) targeted histone H3 lysine 9/14 acetylation (H3K9/14ac), a transcriptionally active mark, or histone H3 lysine 9 dimethylation (H3K9me2), which is associated with transcriptional repression, specifically to the Cdk5 locus in NAc in vivo We found that Cdk5-ZFP transcription factors are sufficient to bidirectionally regulate Cdk5 gene expression via enrichment of their respective histone modifications. We examined the behavioral consequences of this epigenetic remodeling and found that Cdk5-targeted H3K9/14ac increased cocaine-induced locomotor behavior, as well as resilience to social stress. Conversely, Cdk5-targeted H3K9me2 attenuated both cocaine-induced locomotor behavior and conditioned place preference, but had no effect on stress-induced social avoidance behavior. The current study provides evidence for the causal role of Cdk5 epigenetic remodeling in NAc in Cdk5 gene expression and in the control of reward and stress responses. Moreover, these data are especially compelling given that previous work demonstrated opposite behavioral phenotypes compared with those reported here upon Cdk5 overexpression or knockdown, demonstrating the importance of targeted epigenetic remodeling tools for studying more subtle molecular changes that contribute to neuropsychiatric disease. SIGNIFICANCE STATEMENT: Addiction and depression are highly heritable diseases, yet it has been difficult to identify gene sequence variations that underlie this heritability. Gene regulation via epigenetic remodeling is an additional mechanism contributing to the neurobiological basis of drug and stress exposure. In particular, epigenetic regulation of the Cdk5 gene alters responses to cocaine and stress in mouse and rat models. In this study, we used a novel technology, zinc-finger engineered transcription factors, to remodel histone proteins specifically at the Cdk5 gene. We found that this is sufficient to regulate the expression of Cdk5 and results in altered behavioral responses to cocaine and social stress. These data provide compelling evidence of the significance of epigenetic regulation in the neurobiological basis of reward- and stress-related neuropsychiatric disease.

Neuropathic pain as a trigger for histone modifications in limbic circuitry.

Chronic pain involves both central and peripheral neuronal plasticity that encompasses changes in the brain, spinal cord, and peripheral nociceptors. Within the forebrain, mesocorticolimbic regions associated with emotional regulation have recently been shown to exhibit lasting gene expression changes in models of chronic pain. To better understand how such enduring transcriptional changes might be regulated within brain structures associated with processing of pain or affect, we examined epigenetic modifications involved with active or permissive transcriptional states (histone H3 lysine 4 mono and trimethylation, and histone H3 lysine 27 acetylation) in periaqueductal gray (PAG), lateral hypothalamus (LH), nucleus accumbens (NAc), and ventral tegmental area (VTA) 5 weeks after sciatic nerve injury in mice to model chronic pain. For both male and female mice in chronic pain, we observed an overall trend for a reduction of these epigenetic markers in periaqueductal gray, LH, and NAc, but not VTA. Moreover, we discovered that some epigenetic modifications exhibited changes associated with pain history, while others were associated with individual differences in pain sensitivity. When taken together, these results suggest that nerve injury leads to chronic chromatin-mediated suppression of transcription in key limbic brain structures and circuits, which may underlie enduring changes in pain processing and sensitivity within these systems.

Overlapping representations of food and social stimuli in mouse VTA dopamine neurons.

Dopamine neurons of the ventral tegmental area (VTADA) respond to food and social stimuli and contribute to both forms of motivation. However, it is unclear whether the same or different VTADA neurons encode these different stimuli. To address this question, we performed two-photon calcium imaging in mice presented with food and conspecifics and found statistically significant overlap in the populations responsive to both stimuli. Both hunger and opposite-sex social experience further increased the proportion of neurons that respond to both stimuli, implying that increasing motivation for one stimulus increases overlap. In addition, single-nucleus RNA sequencing revealed significant co-expression of feeding- and social-hormone-related genes in individual VTADA neurons. Taken together, our functional and transcriptional data suggest overlapping VTADA populations underlie food and social motivation.

Overlapping representations of food and social stimuli in VTA dopamine neurons.

Dopamine neurons of the ventral tegmental area (VTA DA ) respond to food and social stimuli and contribute to both forms of motivation. However, it is unclear if the same or different VTA DA neurons encode these different stimuli. To address this question, we performed 2-photon calcium imaging in mice presented with food and conspecifics, and found statistically significant overlap in the populations responsive to both stimuli. Both hunger and opposite-sex social experience further increased the proportion of neurons that respond to both stimuli, implying that modifying motivation for one stimulus affects responses to both stimuli. In addition, single-nucleus RNA sequencing revealed significant co-expression of feeding- and social-hormone related genes in individual VTA DA neurons. Taken together, our functional and transcriptional data suggest overlapping VTA DA populations underlie food and social motivation.

Oxycodone withdrawal induces HDAC1/HDAC2-dependent transcriptional maladaptations in the reward pathway in a mouse model of peripheral nerve injury.

The development of physical dependence and addiction disorders due to misuse of opioid analgesics is a major concern with pain therapeutics. We developed a mouse model of oxycodone exposure and subsequent withdrawal in the presence or absence of chronic neuropathic pain. Oxycodone withdrawal alone triggered robust gene expression adaptations in the nucleus accumbens, medial prefrontal cortex and ventral tegmental area, with numerous genes and pathways selectively affected by oxycodone withdrawal in mice with peripheral nerve injury. Pathway analysis predicted that histone deacetylase (HDAC) 1 is a top upstream regulator in opioid withdrawal in nucleus accumbens and medial prefrontal cortex. The novel HDAC1/HDAC2 inhibitor, Regenacy Brain Class I HDAC Inhibitor (RBC1HI), attenuated behavioral manifestations of oxycodone withdrawal, especially in mice with neuropathic pain. These findings suggest that inhibition of HDAC1/HDAC2 may provide an avenue for patients with chronic pain who are dependent on opioids to transition to non-opioid analgesics.

Chronic Intermittent Hypoxia Enhances Pathological Tau Seeding, Propagation, and Accumulation and Exacerbates Alzheimer-like Memory and Synaptic Plasticity Deficits and Molecular Signatures.

BACKGROUND: Obstructive sleep apnea, characterized by sleep fragmentation and chronic intermittent hypoxia (CIH), is a risk factor for Alzheimer's disease (AD) progression. Recent epidemiological studies point to CIH as the best predictor of developing cognitive decline and AD in older adults with obstructive sleep apnea. However, the precise underlying mechanisms remain unknown. This study was undertaken to evaluate the effect of CIH on pathological human tau seeding, propagation, and accumulation; cognition; synaptic plasticity; neuronal network excitability; and gene expression profiles in a P301S human mutant tau mouse model of AD and related tauopathies. METHODS: We exposed 4- to 4.5-month-old male P301S and wild-type mice to an 8-week CIH protocol (6-min cycle: 21% O2 to 8% O2 to 21% O2, 80 cycles per 8 hours during daytime) and assessed its effect on tau pathology and various AD-related phenotypic and molecular signatures. Age- and sex-matched P301S and wild-type mice were reared in normoxia (21% O2) as experimental controls. RESULTS: CIH significantly enhanced pathological human tau seeding and spread across connected brain circuitry in P301S mice; it also increased phosphorylated tau load. CIH also exacerbated memory and synaptic plasticity deficits in P301S mice. However, CIH had no effect on seizure susceptibility and network hyperexcitability in these mice. Finally, CIH exacerbated AD-related pathogenic molecular signaling in P301S mice. CONCLUSIONS: CIH-induced increase in pathologic human tau seeding and spread and exacerbation of other AD-related impairments provide new insights into the role of CIH and obstructive sleep apnea in AD pathogenesis.

Sex-Specific Role for SLIT1 in Regulating Stress Susceptibility.

BACKGROUND: Major depressive disorder is a pervasive and debilitating syndrome characterized by mood disturbances, anhedonia, and alterations in cognition. While the prevalence of major depressive disorder is twice as high for women as men, little is known about the molecular mechanisms that drive sex differences in depression susceptibility. METHODS: We discovered that SLIT1, a secreted protein essential for axonal navigation and molecular guidance during development, is downregulated in the adult ventromedial prefrontal cortex (vmPFC) of women with depression compared with healthy control subjects, but not in men with depression. This sex-specific downregulation of Slit1 was also observed in the vmPFC of mice exposed to chronic variable stress. To identify a causal, sex-specific role for SLIT1 in depression-related behavioral abnormalities, we performed knockdown (KD) of Slit1 expression in the vmPFC of male and female mice. RESULTS: When combined with stress exposure, vmPFC Slit1 KD reflected the human condition by inducing a sex-specific increase in anxiety- and depression-related behaviors. Furthermore, we found that vmPFC Slit1 KD decreased the dendritic arborization of vmPFC pyramidal neurons and decreased the excitability of the neurons in female mice, effects not observed in males. RNA sequencing analysis of the vmPFC after Slit1 KD in female mice revealed an augmented transcriptional stress signature. CONCLUSIONS: Together, our findings establish a crucial role for SLIT1 in regulating neurophysiological and transcriptional responses to stress within the female vmPFC and provide mechanistic insight into novel signaling pathways and molecular factors influencing sex differences in depression susceptibility.

Comparative Transcriptional Analyses in the Nucleus Accumbens Identifies RGS2 as a Key Mediator of Depression-Related Behavior.

BACKGROUND: Major depressive disorder is one of the most commonly diagnosed mental illnesses worldwide, with a higher prevalence in women than in men. Although currently available pharmacological therapeutics help many individuals, they are not effective for most. Animal models have been important for the discovery of molecular alterations in stress and depression, but difficulties in adapting animal models of depression for females has impeded progress in developing novel therapeutic treatments that may be more efficacious for women. METHODS: Using the California mouse social defeat model, we took a multidisciplinary approach to identify stress-sensitive molecular targets that have translational relevance for women. We determined the impact of stress on transcriptional profiles in male and female California mouse nucleus accumbens (NAc) and compared these results with data from postmortem samples of the NAc from men and women diagnosed with major depressive disorder. RESULTS: Our cross-species computational analyses identified Rgs2 (regulator of G protein signaling 2) as a transcript downregulated by social defeat stress in female California mice and in women with major depressive disorder. RGS2 plays a key role in signal regulation of neuropeptide and neurotransmitter receptors. Viral vector-mediated overexpression of Rgs2 in the NAc restored social approach and sucrose preference in stressed female California mice. CONCLUSIONS: These studies show that Rgs2 acting in the NAc has functional properties that translate to changes in anxiety- and depression-related behavior. Future studies should investigate whether targeting Rgs2 represents a novel target for treatment-resistant depression in women.

Crystallin Mu in Medial Amygdala Mediates the Effect of Social Experience on Cocaine Seeking in Males but Not in Females.

BACKGROUND: Social experiences influence susceptibility to substance use disorder. The adolescent period is associated with the development of social reward and is exceptionally sensitive to disruptions to reward-associated behaviors by social experiences. Social isolation (SI) during adolescence alters anxiety- and reward-related behaviors in adult males, but little is known about females. The medial amygdala (meA) is a likely candidate for the modulation of social influence on drug reward because it regulates social reward, develops during adolescence, and is sensitive to social stress. However, little is known regarding how the meA responds to drugs of abuse. METHODS: We used adolescent SI coupled with RNA sequencing to better understand the molecular mechanisms underlying meA regulation of social influence on reward. RESULTS: We show that SI in adolescence, a well-established preclinical model for addiction susceptibility, enhances preference for cocaine in male but not in female mice and alters cocaine-induced protein and transcriptional profiles within the adult meA particularly in males. To determine whether transcriptional mechanisms within the meA are important for these behavioral effects, we manipulated Crym expression, a sex-specific key driver gene identified through differential gene expression and coexpression network analyses, specifically in meA neurons. Overexpression of Crym, but not another key driver that did not meet our sex-specific criteria, recapitulated the behavioral and transcriptional effects of adolescent SI. CONCLUSIONS: These results show that the meA is essential for modulating the sex-specific effects of social experience on drug reward and establish Crym as a critical mediator of sex-specific behavioral and transcriptional plasticity.

Impact of Early Life Stress on Reward Circuit Function and Regulation.

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

Long-term behavioral and cell-type-specific molecular effects of early life stress are mediated by H3K79me2 dynamics in medium spiny neurons.

Animals susceptible to chronic social defeat stress (CSDS) exhibit depression-related behaviors, with aberrant transcription across several limbic brain regions, most notably in the nucleus accumbens (NAc). Early life stress (ELS) promotes susceptibility to CSDS in adulthood, but associated enduring changes in transcriptional control mechanisms in the NAc have not yet been investigated. In this study, we examined long-lasting changes to histone modifications in the NAc of male and female mice exposed to ELS. Dimethylation of lysine 79 of histone H3 (H3K79me2) and the enzymes (DOT1L and KDM2B) that control this modification are enriched in D2-type medium spiny neurons and are shown to be crucial for the expression of ELS-induced stress susceptibility. We mapped the site-specific regulation of this histone mark genome wide to reveal the transcriptional networks it modulates. Finally, systemic delivery of a small molecule inhibitor of DOT1L reversed ELS-induced behavioral deficits, indicating the clinical relevance of this epigenetic mechanism.

Chronic stress and antidepressant treatment alter purine metabolism and beta oxidation within mouse brain and serum.

Major depressive disorder (MDD) is a complex condition with unclear pathophysiology. Molecular disruptions within limbic brain regions and the periphery contribute to depression symptomatology and a more complete understanding the diversity of molecular changes that occur in these tissues may guide the development of more efficacious antidepressant treatments. Here, we utilized a mouse chronic social stress model for the study of MDD and performed metabolomic, lipidomic, and proteomic profiling on serum plus several brain regions (ventral hippocampus, nucleus accumbens, and medial prefrontal cortex) of susceptible, resilient, and unstressed control mice. To identify how commonly used tricyclic antidepressants impact the molecular composition in these tissues, we treated stress-exposed mice with imipramine and repeated our multi-OMIC analyses. Proteomic analysis identified three serum proteins reduced in susceptible animals; lipidomic analysis detected differences in lipid species between resilient and susceptible animals in serum and brain; and metabolomic analysis revealed dysfunction of purine metabolism, beta oxidation, and antioxidants, which were differentially associated with stress susceptibility vs resilience by brain region. Antidepressant treatment ameliorated stress-induced behavioral abnormalities and affected key metabolites within outlined networks, most dramatically in the ventral hippocampus. This work presents a resource for chronic social stress-induced, tissue-specific changes in proteins, lipids, and metabolites and illuminates how molecular dysfunctions contribute to individual differences in stress sensitivity.

Sex-Specific Role for the Long Non-coding RNA LINC00473 in Depression.

Depression is a common disorder that affects women at twice the rate of men. Here, we report that long non-coding RNAs (lncRNAs), a recently discovered class of regulatory transcripts, represent about one-third of the differentially expressed genes in the brains of depressed humans and display complex region- and sex-specific patterns of regulation. We identified the primate-specific, neuronal-enriched gene LINC00473 as downregulated in prefrontal cortex (PFC) of depressed females but not males. Using viral-mediated gene transfer to express LINC00473 in adult mouse PFC neurons, we mirrored the human sex-specific phenotype by inducing stress resilience solely in female mice. This sex-specific phenotype was accompanied by changes in synaptic function and gene expression selectively in female mice and, along with studies of human neuron-like cells in culture, implicates LINC00473 as a CREB effector. Together, our studies identify LINC00473 as a female-specific driver of stress resilience that is aberrant in female depression.

A novel role for E2F3b in regulating cocaine action in the prefrontal cortex.

Drug abuse is a multifaceted disorder that involves maladaptive decision making. Long-lasting changes in the addicted brain are mediated by a complex circuit of brain reward regions. The prefrontal cortex (PFC) is one region in which chronic drug exposure changes expression and function of upstream transcriptional regulators to alter drug responses and aspects of the addicted phenotype. We reported recently that the transcription factor E2F3a is a critical mediator of cocaine responses in the nucleus accumbens. E2F3a is one of two splice variants of the E2f3 gene; the other is E2F3b. Another recent study predicted E2F3 as an upstream regulator of the transcriptional response to cocaine self-administration (SA) in PFC. Based on previous findings that E2F3a and E2F3b have divergent regulatory roles, we set out to study the putative transcriptional role of these transcripts in PFC in the context of repeated I.P. cocaine exposure. We implemented viral-mediated isoform-specific gene manipulation, RNA-sequencing, advanced bioinformatics analyses, and animal behavior to determine how E2F3a and E2F3b contribute to persistent cocaine-induced transcriptional changes in PFC. We show that E2F3b, but not E2F3a, in PFC is critical for cocaine locomotor and place preference behaviors. Interestingly, RNA-seq of PFC following E2f3b overexpression or I.P. cocaine exposure showed very different effects on expression levels of differentially expressed genes. However, we found that E2F3b drives a similar transcriptomic pattern to that of cocaine SA with overlapping upstream regulators and downstream pathways predicted. These findings reveal a novel transcriptional mechanism in PFC that controls behavioral and molecular responses to cocaine.

Progress in Epigenetics of Depression.

Depression is a prevalent and complex psychiatric syndrome. Epigenetic mechanisms bridge the genetic and environmental factors that contribute to the pathophysiology of depression. A surge of research over the last decade has identified changes in DNA methylation, histone modifications, histone organization, and noncoding RNAs associated with depression and stress-induced depression-like behavior in animal models. We focus here on associations of epigenetic factors concurrent with depression and depression-like behavior, although risk for depression and some of the associated epigenetic changes are known to have developmental origins. Finally, emerging technology may enable breakthroughs in the ability to rescue depression-associated epigenetic modifications at specific genes, greatly enhancing specificity of future potential therapeutic treatments.