DISC1-related signaling pathways in adult neurogenesis of the hippocampus

SRSF10 regulates migration of neural progenitor cells and granule cells and affects the formation of dentate gyrus during the development of mouse hippocampus

Hippocampus is a critical component of the central nervous system. SRSF10 is expressed in central nervous system and plays important roles in maintaining normal brain functions. However, its role in hippocampus development is unknown. In this study, using SRSF10 conditional knock-out mice in neural progenitor cells (NPCs), we found that dysfunction of SRSF10 leads to developmental defects in the dentate gyrus of hippocampus, which manifests as the reduced length and wider suprapyramidal blade and infrapyramidal blade.Furthermore, we proved that loss of SRSF10 in NPCs caused inhibition of the differentiation activity and the abnormal migration of NPCs and granule cells, resulting in reduced granule cells and more ectopic granule cells dispersed in the molecular layer and hilus. Finally, we found that the abnormal migration may be caused by the radial glia scaffold and the reduced DISC1 expression in NPCs. Together, our results indicate that SRSF10 is required for the cell migration and formation of dentate gyrus during the development of hippocampus.

Prenatal stress alters transcription of NMDA-type glutamate receptors in the hippocampus

Prenatal stress increases the risk of neurodevelopmental disorders. NMDA-type glutamate receptor (NMDAR) activity plays an important pathophysiological role in the cortico-hippocampal circuit in these disorders. We tested the hypothesis that transcription of NMDAR subunits is modified in the frontal cortex (FCx) and hippocampus after exposure to prenatal restraint stress (PRS) in mice. At 10 weeks of age, male PRS offspring (n = 20) and non-stressed controls (NS, n = 20) were treated with haloperidol (1 mg/kg), clozapine (5 mg/kg) or saline twice daily for 5 days, before measuring social approach (SOC). Saline-treated and haloperidol-treated PRS mice had reduced SOC relative to NS (P < 0.01), but clozapine-treated PRS mice had similar SOC to NS mice. These effects of PRS were associated with increased transcription of NMDAR subunits encoded by GRIN2A and GRIN2B genes in the hippocampus but not FCx. GRIN transcription in FCx correlated positively with SOC, but hippocampal GRIN transcription had negative correlation with SOC. The ratio of GRIN2A/GRIN2B transcription is known to increase during development but was lower in PRS mice. These results suggest that GRIN2A and GRIN2B transcript levels are modified in the hippocampus by PRS, leading to life-long deficits in social behavior. These data have some overlap with the molecular pathophysiology of schizophrenia. Similar to PRS in mice, schizophrenia, has been associated with social withdrawal, with increased GRIN2 expression in the hippocampus, and reduced GRIN2A/GRIN2B expression ratios in the hippocampus. These findings suggest that PRS in mice may have construct validity as a preclinical model for antipsychotic drug development.

miR-377-3p Regulates Hippocampal Neurogenesis via the Zfp462-Pbx1 Pathway and Mediates Anxiety-Like Behaviors in Prenatal Hypoxic Offspring

Prenatal hypoxia (PH) is one of the most common complications of obstetrics and is closely associated with many neurological disorders such as depression, anxiety, and cognitive impairment. Our previous study found that Zfp462 heterozygous (Het) mice exhibit significant anxiety-like behavior. Interestingly, offspring mice with PH also have anxiety-like behaviors in adulthood, accompanied by reduced expression of Zfp462 and increased expression of miR-377-3p; however, the exact regulatory mechanisms remain unclear. In this study, western blotting, gene knockdown, immunofluorescence, dual-luciferase reporter assay, immunoprecipitation, cell transfection with miR-377-3p mimics or inhibitors, quantitative real-time PCR, and rescue assay were used to detect changes in the miR-377-3p-Zfp462-Pbx1 (pre-B-cell leukemia homeobox1) pathway in the brains of prenatal hypoxic offspring to explain the pathogenesis of anxiety-like behaviors. We found that Zfp462 deficiency promoted Pbx1 protein degradation through ubiquitination and that Zfp462 Het mice showed downregulation of the protein kinase B (PKB, also called Akt)-glycogen synthase kinase-3β (GSK3β)-cAMP response element-binding protein (CREB) pathway and hippocampal neurogenesis with anxiety-like behavior. In addition, PH mice exhibited upregulation of miR-377-3p, downregulation of Zfp462/Pbx1-Akt-GSK3β-CREB pathway activity, reduced hippocampal neurogenesis, and an anxiety-like phenotype. Intriguingly, miR-377-3p directly targets the 3'UTR of Zfp462 mRNA to regulate Zfp462 expression. Importantly, microinjection of miR-377-3p antagomir into the hippocampal dentate gyrus of PH mice upregulated Zfp462/Pbx1-Akt-GSK3β-CREB pathway activity, increased hippocampal neurogenesis, and improved anxiety-like behaviors. Collectively, our findings demonstrated a crucial role for miR-377-3p in the regulation of hippocampal neurogenesis and anxiety-like behaviors via the Zfp462/Pbx1-Akt-GSK3β-CREB pathway. Therefore, miR-377-3p could be a potential therapeutic target for anxiety-like behavior in prenatal hypoxic offspring.

Altered hippocampal neurogenesis in a mouse model of autism revealed by genetic polymorphisms and by atypical development of newborn neurons

Individuals with autism spectrum disorder (ASD) often exhibit atypical hippocampal anatomy and connectivity throughout their lifespan, potentially linked to alterations in the neurogenic process within the hippocampus. In this study, we performed an in-silico analysis to identify single-nucleotide polymorphisms (SNPs) in genes relevant to adult neurogenesis in the C58/J model of idiopathic autism. We found coding non-synonymous (Cn) SNPs in 33 genes involved in the adult neurogenic process, as well as in 142 genes associated with the signature genetic profile of neural stem cells (NSC) and neural progenitors. Based on the potential alterations in adult neurogenesis predicted by the in-silico analysis, we evaluated the number and distribution of newborn neurons in the dentate gyrus (DG) of young adult C58/J mice. We found a reduced number of newborn cells in the whole DG, a higher proportion of early neuroblasts in the subgranular layer (SGZ), and a lower proportion of neuroblasts with morphological maturation signs in the granule cell layer (GCL) of the DG compared to C57BL/6J mice. The observed changes may be associated with a delay in the maturation trajectory of newborn neurons in the C58/J strain, linked to the Cn SNPs in genes involved in adult hippocampal neurogenesis.

DISC1 and reelin interact to alter cognition, inhibition, and neurogenesis in a novel mouse model of schizophrenia

The etiology of schizophrenia (SCZ) is multifactorial, and depending on a host of genetic and environmental factors. Two putative SCZ susceptibility genes, Disrupted-in-Schizophrenia-1 (DISC1) and reelin (RELN), interact at a molecular level, suggesting that combined disruption of both may lead to an intensified SCZ phenotype. To examine this gene-gene interaction, we produced a double mutant mouse line. Mice with heterozygous RELN haploinsufficiency were crossed with mice expressing dominant-negative c-terminal truncated human DISC1 to produce offspring with both mutations (HRM/DISC1 mice). We used an array of behavioral tests to generate a behavioral phenotype for these mice, then examined the prefrontal cortex and hippocampus using western blotting and immunohistochemistry to probe for SCZ-relevant molecular and cellular alterations. Compared to wild-type controls, HRM/DISC1 mice demonstrated impaired pre-pulse inhibition, altered cognition, and decreased activity. Diazepam failed to rescue anxiety-like behaviors, paradoxically increasing activity in HRM/DISC1 mice. At a cellular level, we found increased α1-subunit containing GABA receptors in the prefrontal cortex, and a reduction in fast-spiking parvalbumin positive neurons. Maturation of adult-born neurons in the hippocampus was also altered in HRM/DISC1 mice. While there was no difference in the total number proliferating cells, more of these cells were in immature stages of development. Homozygous DISC1 mutation combined with RELN haploinsufficiency produces a complex phenotype with neuropsychiatric characteristics relevant to SCZ and related disorders, expanding our understanding of how multiple genetic susceptibility factors might interact to influence the variable presentation of these disorders.

Schizophrenia in the genetic era: a review from development history, clinical features and genomic research approaches to insights of susceptibility genes

Schizophrenia is a devastating neuropsychiatric disorder affecting 1% of the world population and ranks as one of the disorders providing the most severe burden for society. Schizophrenia etiology remains obscure involving multi-risk factors, such as genetic, environmental, nutritional, and developmental factors. Complex interactions of genetic and environmental factors have been implicated in the etiology of schizophrenia. This review provides an overview of the historical origins, pathophysiological mechanisms, diagnosis, clinical symptoms and corresponding treatment of schizophrenia. In addition, as schizophrenia is a polygenic, genetic disorder caused by the combined action of multiple micro-effective genes, we further detail several approaches, such as candidate gene association study (CGAS) and genome-wide association study (GWAS), which are commonly used in schizophrenia genomics studies. A number of GWASs about schizophrenia have been performed with the hope to identify novel, consistent and influential risk genetic factors. Finally, some schizophrenia susceptibility genes have been identified and reported in recent years and their biological functions are also listed. This review may serve as a summary of past research on schizophrenia genomics and susceptibility genes (NRG1, DISC1, RELN, BDNF, MSI2), which may point the way to future schizophrenia genetics research. In addition, depending on the above discovery of susceptibility genes and their exact function, the development and application of antipsychotic drugs will be promoted in the future.

Electroconvulsive Therapy Reduces Protein Expression Level of EP300 and Improves Psychiatric Symptoms and Disturbance of Thought in Patients with Schizophrenia

Objective

Although electroconvulsive therapy (ECT) has been employed as an effective treatment strategy and to improve mental symptoms in schizophrenia (SCZ), its action mechanisms remain unclear. Our previous study found that some genes and biological pathways were closely related to ECT through genetic technology analysis, such as LTP pathway and EP300. This study combined with healthy controls and symptomatology analysis to further explore the changes of expression of EP300 protein in treatment and related symptoms of SCZ.

Methods

One hundred and one patients with SCZ and 45 healthy controls (HCs) were enrolled in this study. Patients with SCZ received acute courses of 6 times bilateral ECT. The peripheral blood of patients with SCZ (BECT: before ECT; AECT: after ECT) and the HCs was collected to calculate the changes of expression level of EP300 protein by enzyme-linked immunosorbent assay. The Positive and Negative Symptoms Scale (PANSS) was used to evaluate the severity of symptoms of SCZ patients and the efficiency of the ECT.

Results

There was a statistical difference of EP300 protein expression in patients with SCZ (BECT and AECT) (F = 114.5, p < 0.05). ECT reduced plasma expression level of EP300 protein in patients with SCZ, which was not statistically different from that in HCs (t = 4.47, p = 0.20). The change of the expression level of EP300 protein in patients with SCZ (BECT and AECT) has a positive correlation with reduction rate of positive symptoms (r = 0.228, p < 0.05) and disturbance of thought (r = 0.219, p < 0.05).

Conclusion

Our study suggests that the expression level of EP300 protein has a significant change in patients with SCZ treating with ECT, and EP300 may have some connections with positive symptoms and disturbance thought of patients with SCZ.

Electroacupuncture improves cognitive impairment in diabetic cognitive dysfunction rats by regulating the mitochondrial autophagy pathway

Background

Diabetes-associated cognitive dysfunction has become a major public health concern. However, the mechanisms driving this disease are elusive. Herein, we explored how electroacupuncture improves learning and memory function in diabetic rats.

Methods

The diabetic model was established by intraperitoneal injection of streptozotocin (STZ) in adult Sprague–Dawley rats. Rats were fed on high-fat and high-sugar diets. Learning and memory functions were assessed using behavioral tests. The hematoxylin and eosin (H&E) staining, Western blotting, real-time PCR, ELISA, immunohistochemistry, and transmission electronic microscopy (TEM) was performed to test related indicators.

Results

High-fat and high-sugar diets impaired learning and memory function in rats, while electroacupuncture treatment reversed these changes. The model group presented highly prolonged escape latency compared to the control group, indicating impaired learning and memory functions. The TEM examination showed that electroacupuncture enhanced Aβ clearance and mitochondrial autophagy in hippocampal neuronal cells by increasing DISC1 expression.

Conclusions

Electroacupuncture improves learning and memory function in diabetic rats by increasing DISC1 expression to promote mitophagy. This enhanced Aβ clearance, alleviating cytotoxicity in hippocampal neuronal cells.

Adult neural stem cells and schizophrenia

Schizophrenia (SCZ) is a devastating and complicated mental disorder accompanied by variable positive and negative symptoms and cognitive deficits. Although many genetic risk factors have been identified, SCZ is also considered as a neurodevelopmental disorder. Elucidation of the pathogenesis and the development of treatment is challenging because complex interactions occur between these genetic risk factors and environment in essential neurodevelopmental processes. Adult neural stem cells share a lot of similarities with embryonic neural stem cells and provide a promising model for studying neuronal development in adulthood. These adult neural stem cells also play an important role in cognitive functions including temporal and spatial memory encoding and context discrimination, which have been shown to be closely linked with many psychiatric disorders, such as SCZ. Here in this review, we focus on the SCZ risk genes and the key components in related signaling pathways in adult hippocampal neural stem cells and summarize their roles in adult neurogenesis and animal behaviors. We hope that this would be helpful for the understanding of the contribution of dysregulated adult neural stem cells in the pathogenesis of SCZ and for the identification of potential therapeutic targets, which could facilitate the development of novel medication and treatment.

CA1 Spike Timing is Impaired in the 129S Inbred Strain During Cognitive Tasks

A spontaneous mutation of the disrupted in schizophrenia 1 (Disc1) gene is carried by the 129S inbred mouse strain. Truncated DISC1 protein in 129S mouse synapses impairs the scaffolding of excitatory postsynaptic receptors and leads to progressive spine dysgenesis. In contrast, C57BL/6 inbred mice carry the wild-type Disc1 gene and exhibit more typical cognitive performance in spatial exploration and executive behavioral tests. Because of the innate Disc1 mutation, adult 129S inbred mice exhibit the behavioral phenotypes of outbred B6 Disc1 knockdown (Disc1^-/-) or Disc1-L-100P mutant strains. Recent studies in Disc1^-/- and L-100P mice have shown that impaired excitation-driven interneuron activity and low hippocampal theta power underlie the behavioral phenotypes that resemble human depression and schizophrenia. The current study compared the firing rate and connectivity profile of putative neurons in the CA1 of freely behaving inbred 129S and B6 mice, which have mutant and wild-type Disc1 genes, respectively. In cognitive behavioral tests, 129S mice had lower exploration scores than B6 mice. Furthermore, the mean firing rate for 129S putative pyramidal (pyr) cells and interneurons (int) was significantly lower than that for B6 CA1 neurons sampled during similar tasks. Analysis of pyr/int connectivity revealed a significant delay in synaptic transmission for 129S putative pairs. Sampled 129S pyr/int pairs also had lower detectability index scores than B6 putative pairs. Therefore, the spontaneous Disc1 mutation in the 129S strain attenuates the firing of putative pyr CA1 neurons and impairs spike timing fidelity during cognitive tasks.

Mind–Body Exercises for PTSD Symptoms, Depression, and Anxiety in Patients With PTSD: A Systematic Review and Meta-Analysis

Objectives

This study aims to systematically analyze the effects of mind–body exercises on post-traumatic stress disorder (PTSD) symptoms, depression, and anxiety in patients with PTSD. Furthermore, it intends to provide scientific evidence-based exercise prescriptions.

Methods

Chinese (i.e., China National Knowledge Infrastructure, VIP Database for Chinese Technical Periodicals, and Wanfang) and English (i.e., Web of Science, PubMed, the Cochrane Library, and EMBASE) databases were used as data sources to search for studies on the effects of mind–body exercises on symptoms associated with patients with PTSD from January 1980 to November 2020. After a rigorous screening, 16 eligible randomized controlled trials (RCTs) were included in the meta-analysis.

Results

Mind–body exercises exerted a significant effect on PTSD symptoms [standard mean difference (SMD) = −0.41, 95% confidence interval (CI) −0.64 to −0.19, p < 0.001], depression (SMD = −0.35, 95% CI: −0.55 to −0.15, p < 0.001), and anxiety (SMD = −0.31, 95% CI: −0.74 to −0.12, p < 0.001) among patients with PTSD. Subgroup analysis demonstrated that 60–150 min per session for 8–16 weeks of mindfulness was more effective in improving symptoms in patients with PTSD under 45 years of age compared with other subgroups. For depression, 150–180 min of yoga exercises once per week was effective. For anxiety, the frequency, timing, duration, and type of mind–body exercises that are most effective in relieving anxiety in patients with PTSD cannot be determined at this time due to the limited number of eligible RCTs.

Conclusions

Mind–body exercises were found to be significantly effective in improving PTSD symptoms, depression, and anxiety in patients with PTSD. Therefore, they can be used as an adjunct to intervention for symptoms of patients with PTSD. However, this conclusion requires further confirmation through additional scientific and objective RCTs.

Systematic Review Registration:

Unique Identifier: INPLASY2020120072.

Progression of behavioral deficits during periadolescent development differs in female and male DISC1 knockout rats

Mutations in the disrupted in schizophrenia-1 (DISC1) gene are associated with an increased risk of developing psychological disorders including schizophrenia, bipolar disorder, and depression. Assessing the impact of knocking out genes, like DISC1, in animal models provides valuable insights into the relationship between the gene and behavioral outcomes. Previous research has relied on mouse models to assess these impacts, however these may not yield as reliable or rich a behavioral analysis as can be obtained using rats. Thus, the goal of the present study was to characterize the behavioral effects of a biallelic functional deletion of the DISC1 gene in the Sprague Dawley rat. Female and male wild type and DISC1 knockout rats were assessed beginning just prior to weaning and during the post-weaning periadolescent period. The primary outcomes evaluated were activity, anxiety, responses to novel objects and conspecifics, and prepulse inhibition. These behaviors were selected as analogous indices of psychological dysfunction in humans. The DISC1 knockout had significant effects on behavior, although the kind and magnitude of deficits was different for females and males: in females, effects included hyperactivity, aversion to novelty, and a modest prepulse inhibition deficit; in males, effects in anxiety and neophobia were mild but their prepulse inhibition deficit was large. These data confirm that the DISC1 knockout rat model is an excellent way to reproduce and study symptoms of psychological disorders and provides compelling evidence for differential consequences of its dysfunction for females and males in the progression and emergence of specific behavioral deficits.

Behavioral Deficits in Mice with Postnatal Disruption of Ndel1 in Forebrain Excitatory Neurons: Implications for Epilepsy and Neuropsychiatric Disorders

Dysfunction of nuclear distribution element-like 1 (Ndel1) is associated with schizophrenia, a neuropsychiatric disorder characterized by cognitive impairment and with seizures as comorbidity. The levels of Ndel1 are also altered in human and models with epilepsy, a chronic condition whose hallmark feature is the occurrence of spontaneous recurrent seizures and is typically associated with comorbid conditions including learning and memory deficits, anxiety, and depression. In this study, we analyzed the behaviors of mice postnatally deficient for Ndel1 in forebrain excitatory neurons (Ndel1 CKO) that exhibit spatial learning and memory deficits, seizures, and shortened lifespan. Ndel1 CKO mice underperformed in species-specific tasks, that is, the nest building, open field, Y maze, forced swim, and dry cylinder tasks. We surveyed the expression and/or activity of a dozen molecules related to Ndel1 functions and found changes that may contribute to the abnormal behaviors. Finally, we tested the impact of Reelin glycoprotein that shows protective effects in the hippocampus of Ndel1 CKO, on the performance of the mutant animals in the nest building task. Our study highlights the importance of Ndel1 in the manifestation of species-specific animal behaviors that may be relevant to our understanding of the clinical conditions shared between neuropsychiatric disorders and epilepsy.

Akt dependent adult hippocampal neurogenesis regulates the behavioral improvement of treadmill running to mice model of post-traumatic stress disorder

Physical exercise is well-established paradigm for improving adult neurogenesis and brain functions. As considered as an alternative therapeutic strategy, treadmill running could reduce cognitive impairment and psychiatric abnormalities associating post-traumatic stress disorder (PTSD), which might associate with the promote effects to adult neurogenesis. In current study, we aimed to address how treadmill exercise benefit adult hippocampal neurogenesis in PTSD model and the underlying molecular mechanism related with Akt signaling. PTSD was induced by exposure to aggressor and treatments were conducted with different intensity of compulsory treadmill running. We observed treadmill running improved hippocampal neurogenesis including proliferation and neural differentiation of neural stem cells (NSCs). Moreover, behavioral tests showed treadmill could attenuate the cognitive deficit and depressive/anxiety like behaviors in correlating with PTSD model. Moreover, treadmill running recovered the Akt activity in hippocampus. Interrupting treadmill running administrated mice with Akt inhibitor GSK690693 resulted in the blocked the effects of treadmill running to hippocampal neurogenesis and behavioral improvement in PTSD mice model. In conclusion, treadmill running could mediate behavioral functions and improve hippocampal neurogenesis in PTSD model by regulating Akt signaling.

Voluntary exercise improves cognitive deficits in female dominant-negative DISC1 transgenic mouse model of neuropsychiatric disorders

OBJECTIVES

Physical exercise has gained increasing interest as a treatment modality that improves prognosis in psychiatric patients. The disrupted in schizophrenia 1 (DISC1) gene is a candidate gene for major mental illness. In this study, we aimed to determine whether voluntary wheel running can improve cognitive deficits of dominant-negative DISC1 transgenic mice (DN-DISC1).

METHODS

DN-DISC1 and control mice (10-week-old male and female) were placed for 14 days in a cage with or without access to a running wheel. Two weeks later, mice underwent behavioural tests evaluating cognition and social approach and recognition.

RESULTS

Voluntary exercise improved performance in the novel object recognition test, restored the impairment in spatial memory in the Y maze, and reversed the deficit in social recognition memory in DN-DISC1 females. DN-DISC1 males did not exhibit behavioural deficits at baseline. Tissue analysis revealed that exercise induced a significant increase in hippocampal expression of doublecortin (DCX), brain-derived neurotrophic factor (BDNF) and cannabinoid receptor type 1 (CB1R) only in DN-DISC1 females.

CONCLUSIONS

Voluntary exercise is beneficial in attenuating cognitive deficits observed in a rodent model relevant for neuropsychiatric disorders. The data add a preclinical aspect to the accumulating clinical data supporting the incorporation of physical exercise to patients' care.

Mechanisms underlying the role of DISC1 in synaptic plasticity

Disrupted in schizophrenia 1 (DISC1) is an important hub protein, forming multimeric complexes by self-association and interacting with a large number of synaptic and cytoskeletal molecules. The synaptic location of DISC1 in the adult brain suggests a role in synaptic plasticity, and indeed, a number of studies have discovered synaptic plasticity impairments in a variety of different DISC1 mutants. This review explores the possibility that DISC1 is an important molecule for organizing proteins involved in synaptic plasticity and examines why mutations in DISC1 impair plasticity. It concentrates on DISC1's role in interacting with synaptic proteins, controlling dendritic structure and cellular trafficking of mRNA, synaptic vesicles and mitochondria. N-terminal directed mutations appear to impair synaptic plasticity through interactions with phosphodiesterase 4B (PDE4B) and hence protein kinase A (PKA)/GluA1 and PKA/cAMP response element-binding protein (CREB) signalling pathways, and affect spine structure through interactions with kalirin 7 (Kal-7) and Rac1. C-terminal directed mutations also impair plasticity possibly through altered interactions with lissencephaly protein 1 (LIS1) and nuclear distribution protein nudE-like 1 (NDEL1), thereby affecting developmental processes such as dendritic structure and spine maturation. Many of the same molecules involved in DISC1's cytoskeletal interactions are also involved in intracellular trafficking, raising the possibility that impairments in intracellular trafficking affect cytoskeletal development and vice versa. While the multiplicity of DISC1 protein interactions makes it difficult to pinpoint a single causal signalling pathway, we suggest that the immediate-term effects of N-terminal influences on GluA1, Rac1 and CREB, coupled with the developmental effects of C-terminal influences on trafficking and the cytoskeleton make up the two main branches of DISC1's effect on synaptic plasticity and dendritic spine stability.

DISC1 Regulates the Proliferation and Migration of Mouse Neural Stem/Progenitor Cells through Pax5, Sox2, Dll1 and Neurog2

Background: Disrupted-in-schizophrenia 1 (DISC1) regulates neurogenesis and is a genetic risk factor for major psychiatric disorders. However, how DISC1 dysfunction affects neurogenesis and cell cycle progression at the molecular level is still unknown. Here, we investigated the role of DISC1 in regulating proliferation, migration, cell cycle progression and apoptosis in mouse neural stem/progenitor cells (MNSPCs) in vitro. Methods: MNSPCs were isolated and cultured from mouse fetal hippocampi. Retroviral vectors or siRNAs were used to manipulate DISC1 expression in MNSPCs. Proliferation, migration, cell cycle progression and apoptosis of altered MNSPCs were analyzed in cell proliferation assays (MTS), transwell system and flow cytometry. A neurogenesis specific polymerase chain reaction (PCR) array was used to identify genes downstream of DISC1, and functional analysis was performed through transfection of expression plasmids and siRNAs. Results: Loss of DISC1 reduced proliferation and migration of MNSPCs, while an increase in DISC1 led to increased proliferation and migration. Meanwhile, an increase in the proportion of cells in G0/G1 phase was concomitant with reduced levels of DISC1, but significant changes were not observed in the number MNSPCs undergoing apoptosis. Paired box gene 5 (Pax5), sex determining region Y-box 2 (Sox2), delta-like1 (Dll1) and Neurogenin2 (Neurog2) emerged as candidate molecules downstream of DISC1, and rescue experiments demonstrated that increased or decreased expression of either molecule regulated proliferation and migration in DISC1-altered MNSPCs. Conclusion: These results suggest that Pax5, Sox2, Dll1 and Neurog2 mediate DISC1 activity in MNSPC proliferation and migration.

From Gene to Behavior: L-Type Calcium Channel Mechanisms Underlying Neuropsychiatric Symptoms

The L-type calcium channels (LTCCs) Cav1.2 and Cav1.3, encoded by the CACNA1C and CACNA1D genes, respectively, are important regulators of calcium influx into cells and are critical for normal brain development and plasticity. In humans, CACNA1C has emerged as one of the most widely reproduced and prominent candidate risk genes for a range of neuropsychiatric disorders, including bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. Separately, CACNA1D has been found to be associated with BD and autism spectrum disorder, as well as cocaine dependence, a comorbid feature associated with psychiatric disorders. Despite growing evidence of a significant link between CACNA1C and CACNA1D and psychiatric disorders, our understanding of the biological mechanisms by which these LTCCs mediate neuropsychiatric-associated endophenotypes, many of which are shared across the different disorders, remains rudimentary. Clinical studies with LTCC blockers testing their efficacy to alleviate symptoms associated with BD, SCZ, and drug dependence have provided mixed results, underscoring the importance of further exploring the neurobiological consequences of dysregulated Cav1.2 and Cav1.3. Here, we provide a review of clinical studies that have evaluated LTCC blockers for BD, SCZ, and drug dependence-associated symptoms, as well as rodent studies that have identified Cav1.2- and Cav1.3-specific molecular and cellular cascades that underlie mood (anxiety, depression), social behavior, cognition, and addiction.

Fragile X related protein 1 (FXR1P) regulates proliferation of adult neural stem cells

Fragile X related protein 1 (FXR1P) is a member of the fragile X family of RNA-binding proteins, which includes FMRP and FXR2P. Both FMRP and FXR2P regulate neurogenesis, a process affected in a number of neurological and neuropsychiatric disorders, including fragile X syndrome. Although FXR1P has been implicated in various developmental processes and neuropsychiatric diseases, its role in neurodevelopment is not well understood. The goal of the present study was to elucidate the function of FXR1P in adult neurogenesis. We used an inducible mouse model that allows us to investigate how FXR1P deficiency in adult neural stem cells (aNSCs) affects proliferation and neuronal differentiation. Deletion of FXR1 in aNSCs resulted in fewer adult-born cells in the dentate gyrus (DG) overall, reducing populations across different stages of neurogenesis, including radial glia-like cells, intermediate progenitors, neuroblasts, immature neurons and neurons. We hypothesized that this reduction in new cell numbers resulted from impaired proliferation, which we confirmed both in vivo and in vitro. We discovered that FXR1P-deficient aNSCs have altered expression of a select number of cell-cycle genes, and we identified the mRNA of cyclin-dependent kinase inhibitor 1A (Cdkn1a, p21) as a direct target of FXR1P. Restoration of p21 mRNA to wild-type levels rescued the proliferation deficit in cells lacking FXR1P, demonstrating that p21 is a mediator of FXR1P in aNSCs. These results indicate that FXR1P plays an important role in regulating aNSC self-renewal and maintenance in the adult brain, which may have implications for a number of neurodevelopmental and psychiatric disorders.

DISC1 as a Possible Genetic Contribution to Opioid Dependence in a Polish Sample

OBJECTIVE

Disrupted-in-schizophrenia 1 (DISC1) has been linked to vulnerability to a variety of psychiatric disorders and neuropsychiatric phenotypes. However, DISC1 has not been frequently examined as a potential risk factor for substance dependence. An association between opioid dependence and DISC1 rs2738888 polymorphism has been recently reported. In addition, opioid dependence was associated with rs6419156 located close to the protein phosphatase 3 catalytic subunit alpha isoform (PPP3CA) gene. The aim of the present study was to examine the associations between opioid dependence with rs2738888 and rs6419156 in an independent sample.

METHOD

The selected polymorphisms were genotyped in a sample of 392 individuals (69.9% male) diagnosed as alcohol- and/or opioid-dependent. A control group (n = 257; 67.7% male) was derived from the Polish National Health Survey (N = 14,350).

RESULTS

The frequency of rs2738888 C allele was higher in controls than in opioid-dependent cases (OR = 0.65, p = .045). Phenotypic-oriented analyses performed within opioid-dependent individuals revealed the association between lifetime suicide attempt and rs2738888. The C allele of rs2738888 had a protective effect on lifetime suicide attempt in opioid-dependent patients (OR = 0.25, p = .003). Rs6419156 was not associated with substance dependence in the examined sample.

CONCLUSIONS

The DISC1 may play an important role in vulnerability to opioid dependence. In addition, DISC1 may also be a genetic risk factor for suicide attempt in opioid-dependent individuals.

Association study of MiRSNPs with schizophrenia, tardive dyskinesia and cognition

MicroRNAs (miRNAs) bind to 3'UTRs of genes and negatively regulate their expression. With ~50% of miRNAs expressing in the brain, they play an important role in neuronal development, plasticity, cognition and neurological disorders. Conserved miRNA targets are present in >60% genes in humans and are under evolutionary pressure to maintain pairing with miRNA. However, such binding may be affected by genetic variant(s) in the target sites (MiRSNPs), thereby altering gene expression. Differential expression of a large number of genes in postmortem brains of schizophrenia (SZ) patients compared to controls has been documented. Thus studying the role of MiRSNPs which are underinvestigated in SZ becomes attractive. We systematically selected 35 MiRSNPs with predicted functional relevance in 3'UTRs of genes shown previously to be associated with SZ, genotyped and tested their association with disease, using independent discovery and replication samples (total n=1017 cases; n=1073 controls). We also explored genetic associations with two sets of quantitative traits, namely tardive dyskinesia (TD) and cognitive functions disrupted in SZ in subsets of the study cohort. In the primary analysis, a significant association of MiRSNP rs7430 at PPP3CC was observed with SZ in the discovery and the replication samples [discovery: P=0.01; OR (95% CI) 1.24 (1.04-1.48); replication: P=0.03; OR (95% CI) 1.20 (1.02-1.43)]. In the exploratory analyses, five SNPs were nominally associated with TD (P values 0.04-0.004). Separately, 12 SNPs were associated with one or more of the eight cognitive domains (P values 0.05-0.003). These associations, particularly the SNP at PPP3CC merit further investigations.

Catecholaminergic neuronal network dysfunction in the frontal lobe of a genetic mouse model of schizophrenia

BACKGROUND

The precise aetiology of schizophrenia remains unclear. The neurodevelopmental hypothesis of schizophrenia has been proposed based on the accumulation of genomic or neuroimaging studies.

OBJECTIVE

In this study, we examined the catecholaminergic neuronal networks in the frontal cortices of disrupted-in-schizophrenia 1 (DISC1) knockout (KO) mice, which are considered to be a useful model of schizophrenia.

METHODS

Six DISC1 homozygous KO mice and six age-matched littermates were used. The animals' brains were cut into 20-μm-thick slices, which were then immunohistochemically stained using an anti-tyrosine hydroxylase (TH) monoclonal antibody.

RESULTS

The TH-immunopositive fibres detected in the orbitofrontal cortices of the DISC1 KO mice were significantly shorter than those seen in the wild-type mice.

CONCLUSION

These neuropathological findings indicate that the hypofrontal symptoms of schizophrenia are associated with higher mental function deficiencies or cognitive dysfunction such as a loss of working memory.

The role of GSK-3 in treatment-resistant depression and links with the pharmacological effects of lithium and ketamine: A review of the literature

BACKGROUND

Since the discovery of antidepressants, new treatments have emerged with fewer side effects but no greater efficacy. Glycogen synthase kinase 3 β (GSK-3β), a kinase known for its activity on glycogen synthesis, has in the last few years raised growing interest in biological psychiatry. Several efficient treatments in major depression have an inhibitory effect on this kinase, which could be targeted in new mood disorder treatments.

METHODS

The aim of this review is to summarize findings concerning the intracellular pharmacologic effects of GSK-3β inhibitors on mood. After a brief description of the intracellular transduction pathways implicated in both GSK-3β and mood disorders, we reviewed the results demonstrating GSK-3β involvement in the effects of lithium and ketamine.

RESULTS

GSK-3β can be inhibited through several mechanisms such as serine phosphorylation or binding in a proteic scaffold and others. Its inhibition is implicated in numerous cellular pathways of interest involved in neuronal growth and architecture, cell survival, neurogenesis or synaptic plasticity. This inhibition appears to be both efficient and sufficient in improving mood in animal models. In human beings, several levels of evidence show GSK-3β inhibition with antidepressant use. Crucially, strong inhibition has been shown with lithium via the proteic scaffold PP2A/β-arrestin/AKT, and with the rapid antidepressant effect of ketamine via p70S6K.

CONCLUSION

Our review focuses on mechanisms whereby the GSK-3β pathway has a part in the antidepressant effect of lithium and ketamine. This article highlights the importance of translational research from cell and animal models to the clinical setting in order to develop innovative therapeutic targets.

The Neuropsychiatric Disease-Associated Gene cacna1c Mediates Survival of Young Hippocampal Neurons

Genetic variations in CACNA1C, which encodes the Cav1.2 subunit of L-type calcium channels (LTCCs), are associated with multiple forms of neuropsychiatric disease that manifest high anxiety in patients. In parallel, mice harboring forebrain-specific conditional knockout of cacna1c (forebrain-Cav1.2 cKO) display unusually high anxiety-like behavior. LTCCs in general, including the Cav1.3 subunit, have been shown to mediate differentiation of neural precursor cells (NPCs). However, it has not previously been determined whether Cav1.2 affects postnatal hippocampal neurogenesis in vivo. Here, we show that forebrain-Cav1.2 cKO mice exhibit enhanced cell death of young hippocampal neurons, with no change in NPC proliferation, hippocampal size, dentate gyrus thickness, or corticosterone levels compared with wild-type littermates. These mice also exhibit deficits in brain levels of brain-derived neurotrophic factor (BDNF), and Cre recombinase-mediated knockdown of adult hippocampal Cav1.2 recapitulates the deficit in young hippocampal neurons survival. Treatment of forebrain-Cav1.2 cKO mice with the neuroprotective agent P7C3-A20 restored the net magnitude of postnatal hippocampal neurogenesis to wild-type levels without ameliorating their deficit in BDNF expression. The role of Cav1.2 in young hippocampal neurons survival may provide new approaches for understanding and treating neuropsychiatric disease associated with aberrations in CACNA1C. Visual Abstract.

Fibroblast Growth Factor 14 Modulates the Neurogenesis of Granule Neurons in the Adult Dentate Gyrus

Adult neurogenesis, the production of mature neurons from progenitor cells in the adult mammalian brain, is linked to the etiology of neurodegenerative and psychiatric disorders. However, a thorough understanding of the molecular elements at the base of adult neurogenesis remains elusive. Here, we provide evidence for a previously undescribed function of fibroblast growth factor 14 (FGF14), a brain disease-associated factor that controls neuronal excitability and synaptic plasticity, in regulating adult neurogenesis in the dentate gyrus (DG). We found that FGF14 is dynamically expressed in restricted subtypes of sex determining region Y-box 2 (Sox2)-positive and doublecortin (DCX)-positive neural progenitors in the DG. Bromodeoxyuridine (BrdU) incorporation studies and confocal imaging revealed that genetic deletion of Fgf14 in Fgf14 ^-/- mice leads to a significant change in the proportion of proliferating and immature and mature newly born adult granule cells. This results in an increase in the late immature and early mature population of DCX and calretinin (CR)-positive neurons. Electrophysiological extracellular field recordings showed reduced minimal threshold response and impaired paired-pulse facilitation at the perforant path to DG inputs in Fgf14 ^-/- compared to Fgf14 ^+/+ mice, supporting disrupted synaptic connectivity as a correlative read-out to impaired neurogenesis. These new insights into the biology of FGF14 in neurogenesis shed light into the signaling pathways associated with disrupted functions in complex brain diseases.

Circuit- and Diagnosis-Specific DNA Methylation Changes at γ-Aminobutyric Acid-Related Genes in Postmortem Human Hippocampus in Schizophrenia and Bipolar Disorder

IMPORTANCE

Dysfunction related to γ-aminobutyric acid (GABA)-ergic neurotransmission in the pathophysiology of major psychosis has been well established by the work of multiple groups across several decades, including the widely replicated downregulation of GAD1. Prior gene expression and network analyses within the human hippocampus implicate a broader network of genes, termed the GAD1 regulatory network, in regulation of GAD1 expression. Several genes within this GAD1 regulatory network show diagnosis- and sector-specific expression changes within the circuitry of the hippocampus, influencing abnormal GAD1 expression in schizophrenia and bipolar disorder.

OBJECTIVE

To investigate the hypothesis that aberrant DNA methylation contributes to circuit- and diagnosis-specific abnormal expression of GAD1 regulatory network genes in psychotic illness.

DESIGN, SETTING, AND PARTICIPANTS

This epigenetic association study targeting GAD1 regulatory network genes was conducted between July 1, 2012, and June 30, 2014. Postmortem human hippocampus tissue samples were obtained from 8 patients with schizophrenia, 8 patients with bipolar disorder, and 8 healthy control participants matched for age, sex, postmortem interval, and other potential confounds from the Harvard Brain Tissue Resource Center, McLean Hospital, Belmont, Massachusetts. We extracted DNA from laser-microdissected stratum oriens tissue of cornu ammonis 2/3 (CA2/3) and CA1 postmortem human hippocampus, bisulfite modified it, and assessed it with the Infinium HumanMethylation450 BeadChip (Illumina, Inc). The subset of CpG loci associated with GAD1 regulatory network genes was analyzed in R version 3.1.0 software (R Foundation) using the minfi package. Findings were validated using bisulfite pyrosequencing.

MAIN OUTCOMES AND MEASURES

Methylation levels at 1308 GAD1 regulatory network-associated CpG loci were assessed both as individual sites to identify differentially methylated positions and by sharing information among colocalized probes to identify differentially methylated regions.

RESULTS

A total of 146 differentially methylated positions with a false detection rate lower than 0.05 were identified across all 6 groups (2 circuit locations in each of 3 diagnostic categories), and 54 differentially methylated regions with P < .01 were identified in single-group comparisons. Methylation changes were enriched in MSX1, CCND2, and DAXX at specific loci within the hippocampus of patients with schizophrenia and bipolar disorder.

CONCLUSIONS AND RELEVANCE

This work demonstrates diagnosis- and circuit-specific DNA methylation changes at a subset of GAD1 regulatory network genes in the human hippocampus in schizophrenia and bipolar disorder. These genes participate in chromatin regulation and cell cycle control, supporting the concept that the established GABAergic dysfunction in these disorders is related to disruption of GABAergic interneuron physiology at specific circuit locations within the human hippocampus.

Multivariate genetic determinants of EEG oscillations in schizophrenia and psychotic bipolar disorder from the BSNIP study

Schizophrenia (SZ) and psychotic bipolar disorder (PBP) are disabling psychiatric illnesses with complex and unclear etiologies. Electroencephalogram (EEG) oscillatory abnormalities in SZ and PBP probands are heritable and expressed in their relatives, but the neurobiology and genetic factors mediating these abnormalities in the psychosis dimension of either disorder are less explored. We examined the polygenic architecture of eyes-open resting state EEG frequency activity (intrinsic frequency) from 64 channels in 105 SZ, 145 PBP probands and 56 healthy controls (HCs) from the multisite BSNIP (Bipolar-Schizophrenia Network on Intermediate Phenotypes) study. One million single-nucleotide polymorphisms (SNPs) were derived from DNA. We assessed eight data-driven EEG frequency activity derived from group-independent component analysis (ICA) in conjunction with a reduced subset of 10,422 SNPs through novel multivariate association using parallel ICA (para-ICA). Genes contributing to the association were examined collectively using pathway analysis tools. Para-ICA extracted five frequency and nine SNP components, of which theta and delta activities were significantly correlated with two different gene components, comprising genes participating extensively in brain development, neurogenesis and synaptogenesis. Delta and theta abnormality was present in both SZ and PBP, while theta differed between the two disorders. Theta abnormalities were also mediated by gene clusters involved in glutamic acid pathways, cadherin and synaptic contact-based cell adhesion processes. Our data suggest plausible multifactorial genetic networks, including novel and several previously identified (DISC1) candidate risk genes, mediating low frequency delta and theta abnormalities in psychoses. The gene clusters were enriched for biological properties affecting neural circuitry and involved in brain function and/or development.

Modulation of the NMDA Receptor Through Secreted Soluble Factors

Synaptic activity is a critical determinant in the formation and development of excitatory synapses in the central nervous system (CNS). The excitatory current is produced and regulated by several ionotropic receptors, including those that respond to glutamate. These channels are in turn regulated through several secreted factors that function as synaptic organizers. Specifically, Wnt, brain-derived neurotrophic factor (BDNF), fibroblast growth factor (FGF), and transforming growth factor (TGF) particularly regulate the N-methyl-D-aspartate receptor (NMDAR) glutamatergic channel. These factors likely regulate early embryonic development and directly control key proteins in the function of important glutamatergic channels. Here, we review the secreted molecules that participate in synaptic organization and discuss the cell signaling behind of this fine regulation. Additionally, we discuss how these factors are dysregulated in some neuropathologies associated with glutamatergic synaptic transmission in the CNS.

No evidence of DISC1-associated morphological changes in the hippocampus, anterior cingulate cortex, or striatum in major depressive disorder cases and healthy controls

BACKGROUND

DISC1 imaging genetics studies in healthy controls, schizophrenia, and bipolar disorder cases have revealed morphological changes in brain regions involved in the pathophysiology of psychiatric disease including the hippocampus, anterior cingulate cortex (ACC), and the striatum. However, many of these studies have yielded discordant findings so there is a need for replication. Furthermore, despite evidence from human genetic studies and animal models implicating DISC1 in major depressive disorder (MDD), a DISC1 imaging genetics study in MDD cases has yet to be published. Thus, using neuroimaging data from MDD cases and a large sample of healthy controls we aimed to identify morphological changes representing neurobiological mechanisms underlying the association between DISC1 and MDD.

METHODS

We utilized structural magnetic resonance imaging (sMRI) data from 512 healthy controls and 171 current MDD (SCID interview) cases, each with genotype data for non-synonymous DISC1 SNPs rs3738401, rs6675281, and rs821616.

RESULTS

Region of interest analyses failed to reveal DISC1-associated morphological changes in the hippocampus, ACC, or striatum in MDD patients and healthy controls. Whole brain exploratory analyses identified a nominally significant cluster mapping to the border of the precentral and postcentral gyri associated with rs821616 in healthy controls only (p(uncorrected)<0.001).

LIMITATIONS

We focused our analyses exclusively on three, but previously heavily studied, SNPs in DISC1.

CONCLUSIONS

Our findings suggest that morphological changes in the hippocampus, ACC, and/or striatum of MDD patients do not represent neurobiological mechanisms underlying the association between DISC1 and MDD. However, we urge replication in independent samples of MDD cases.

Loss of the mu opioid receptor induces strain-specific alterations in hippocampal neurogenesis and spatial learning

Alterations in hippocampal neurogenesis affect spatial learning, though, the relative contributions of cell proliferation and cell survival on this process are poorly understood. The current study utilized mu opioid receptor (MOR-1) knockout (KO) mice on two background strains, C57BL/6 and 129S6, to assess cell survival as well as determine the impact on spatial learning using the Morris water maze. These experiments were designed to extend prior work showing that both C57BL/6 and 129S6 MOR-1 KO mice have an increased number of proliferating cells in the dentate gyrus (DG) when compared to wild-type (WT) mice. The current study indicates that newly born neurons in the DG of C57BL/6 MOR-1 KO mice exhibit enhanced survival when compared to WT mice, while new neurons in the DG of 129S6 MOR-1 KO mice do not. In addition, C57BL/6 MOR-1 KO mice have a lower number of apoptotic cells in the DG compared to WT mice while, in contrast, 129S6 MOR-1 KO mice have a higher number of apoptotic cells in this region. These alterations collectively contribute to an increase in the granule cell number in the DG of C57BL/6 MOR-1 KO mice, while the total number of granule cells in 129S6 MOR-1 KO mice is unchanged. Thus, although C57BL/6 and 129S6 MOR-1 KO mice both exhibit increased cell proliferation in the DG, the impact of the MOR-1 mutation on cell survival differs between strains. Furthermore, the decrease in DG cell survival displayed by 129S6 MOR-1 KO mice is correlated with functional deficits in spatial learning, suggesting that MOR-1-dependent alterations in the survival of new neurons in the DG, and not MOR-1-dependent changes in proliferation of progenitor cells in the DG, is important for spatial learning.

Formation of chimeric genes by copy-number variation as a mutational mechanism in schizophrenia

Chimeric genes can be caused by structural genomic rearrangements that fuse together portions of two different genes to create a novel gene. We hypothesize that brain-expressed chimeras may contribute to schizophrenia. Individuals with schizophrenia and control individuals were screened genome wide for copy-number variants (CNVs) that disrupted two genes on the same DNA strand. Candidate events were filtered for predicted brain expression and for frequency < 0.001 in an independent series of 20,000 controls. Four of 124 affected individuals and zero of 290 control individuals harbored such events (p = 0.002); a 47 kb duplication disrupted MATK and ZFR2, a 58 kb duplication disrupted PLEKHD1 and SLC39A9, a 121 kb duplication disrupted DNAJA2 and NETO2, and a 150 kb deletion disrupted MAP3K3 and DDX42. Each fusion produced a stable protein when exogenously expressed in cultured cells. We examined whether these chimeras differed from their parent genes in localization, regulation, or function. Subcellular localizations of DNAJA2-NETO2 and MAP3K3-DDX42 differed from their parent genes. On the basis of the expression profile of the MATK promoter, MATK-ZFR2 is likely to be far more highly expressed in the brain during development than the ZFR2 parent gene. MATK-ZFR2 includes a ZFR2-derived isoform that we demonstrate localizes preferentially to neuronal dendritic branch sites. These results suggest that the formation of chimeric genes is a mechanism by which CNVs contribute to schizophrenia and that, by interfering with parent gene function, chimeras may disrupt critical brain processes, including neurogenesis, neuronal differentiation, and dendritic arborization.

Neurodevelopment in schizophrenia: the role of the wnt pathways

OBJECTIVES

To review the role of Wnt pathways in the neurodevelopment of schizophrenia.

METHODS

SYSTEMATIC PUBMED SEARCH, USING AS KEYWORDS ALL THE TERMS RELATED TO THE WNT PATHWAYS AND CROSSING THEM WITH EACH OF THE FOLLOWING AREAS: normal neurodevelopment and physiology, neurodevelopmental theory of schizophrenia, schizophrenia, and antipsychotic drug action.

RESULTS

Neurodevelopmental, behavioural, genetic, and psychopharmacological data point to the possible involvement of Wnt systems, especially the canonical pathway, in the pathophysiology of schizophrenia and in the mechanism of antipsychotic drug action. The molecules most consistently found to be associated with abnormalities or in antipsychotic drug action are Akt1, glycogen synthase kinase3beta, and beta-catenin. However, the extent to which they contribute to the pathophysiology of schizophrenia or to antipsychotic action remains to be established.

CONCLUSIONS

The study of the involvement of Wnt pathway abnormalities in schizophrenia may help in understanding this multifaceted clinical entity; the development of Wnt-related pharmacological targets must await the collection of more data.

Maturation and integration of adult born hippocampal neurons: signal convergence onto small Rho GTPases

Adult neurogenesis, restricted to specific regions in the mammalian brain, represents one of the most interesting forms of plasticity in the mature nervous system. Adult-born hippocampal neurons play important roles in certain forms of learning and memory, and altered hippocampal neurogenesis has been associated with a number of neuropsychiatric diseases such as major depression and epilepsy. Newborn neurons go through distinct developmental steps, from a dividing neurogenic precursor to a synaptically integrated mature neuron. Previous studies have uncovered several molecular signaling pathways involved in distinct steps of this maturational process. In this context, the small Rho GTPases, Cdc42, Rac1, and RhoA have recently been shown to regulate the morphological and synaptic maturation of adult-born dentate granule cells in vivo. Distinct upstream regulators, including growth factors that modulate maturation and integration of newborn neurons have been shown to also recruit the small Rho GTPases. Here we review recent findings and highlight the possibility that small Rho GTPases may act as central assimilators, downstream of critical input onto adult-born hippocampal neurons contributing to their maturation and integration into the existing dentate gyrus (DG) circuitry.