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The effective treatment of bipolar disorder (BD) represents a significant unmet medical need. Although lithium remains a mainstay of treatment for BD, limited knowledge regarding how it modulates affective behavior has proven an obstacle to discovering more effective mood stabilizers with fewer adverse side effects. One potential mechanism of action of lithium is through inhibition of the serine/threonine protein kinase GSK3β, however, relevant substrates whose change in phosphorylation may mediate downstream changes in neuroplasticity remain poorly understood. Here, we used human induced pluripotent stem cell (hiPSC)-derived neuronal cells and stable isotope labeling by amino acids in cell culture (SILAC) along with quantitative mass spectrometry to identify global changes in the phosphoproteome upon inhibition of GSK3α/β with the highly selective, ATP-competitive inhibitor CHIR-99021. Comparison of phosphorylation changes to those induced by therapeutically relevant doses of lithium treatment led to the identification of collapsin response mediator protein 2 (CRMP2) as being highly sensitive to both treatments as well as an extended panel of structurally distinct GSK3α/β inhibitors. On this basis, a high-content image-based assay in hiPSC-derived neurons was developed to screen diverse compounds, including FDA-approved drugs, for their ability to mimic lithium’s suppression of CRMP2 phosphorylation without directly inhibiting GSK3β kinase activity. Systemic administration of a subset of these CRMP2-phosphorylation suppressors were found to mimic lithium’s attenuation of amphetamine-induced hyperlocomotion in mice. Taken together, these studies not only provide insights into the neural substrates regulated by lithium, but also provide novel human neuronal assays for supporting the development of mechanism-based therapeutics for BD and related neuropsychiatric disorders.

A subset of individuals with major depressive disorder (MDD) elects treatment with complementary and alternative medicines (CAMs), including the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Previous studies in rodents suggest that DHA modulates neurodevelopmental processes, including adult neurogenesis and neuroplasticity, but the molecular and cellular mechanisms of DHA's potential therapeutic effect in the context of human neurobiology have not been well established. Here we sought to address this knowledge gap by investigating the effects of DHA using human iPSC-derived neural progenitor cells (NPCs) and post-mitotic neurons using pathway-selective reporter genes, multiplexed mRNA expression profiling, and a panel of metabolism-based viability assays. Finally, real-time, live-cell imaging was employed to monitor neurite outgrowth upon DHA treatment. Overall, these studies showed that DHA treatment (0–50 μM) significantly upregulated both WNT and CREB signaling pathways in human neuronal cells in a dose-dependent manner with 2- to 3-fold increases in pathway activation. Additionally, we observed that DHA treatment enhanced survival of iPSC-derived NPCs and differentiation of post-mitotic neurons with live-cell imaging, revealing increased neurite outgrowth with DHA treatment within 24 h. Taken together, this study provides evidence that DHA treatment activates critical pathways regulating neuroplasticity, which may contribute to enhanced neuronal cell viability and neuronal connectivity. The extent to which these pathways represent molecular mechanisms underlying the potential beneficial effects of omega-3 fatty acids in MDD and other brain disorders merits further investigation.

Frontotemporal dementia (FTD) arises from neurodegeneration in the frontal, insular, and anterior temporal lobes. Autosomal dominant causes of FTD include heterozygous mutations in the GRN gene causing haploinsufficiency of progranulin (PGRN) protein. Recently, histone deacetylase (HDAC) inhibitors have been identified as enhancers of PGRN expression, although the mechanisms through which GRN is epigenetically regulated remain poorly understood. Using a chemogenomic toolkit, including optoepigenetic probes, we show that inhibition of class I HDACs is sufficient to upregulate PGRN in human neurons, and only inhibitors with apparent fast binding to their target HDAC complexes are capable of enhancing PGRN expression. Moreover, we identify regions in the GRN promoter in which elevated H3K27 acetylation and transcription factor EB (TFEB) occupancy correlate with HDAC-inhibitor-mediated upregulation of PGRN. These findings have implications for epigenetic and cis-regulatory mechanisms controlling human GRN expression and may advance translational efforts to develop targeted therapeutics for treating PGRN-deficient FTD.

Stochastic mechanisms are ubiquitous in biological systems. Biochemical reactions that involve small numbers of molecules are intrinsically noisy, being dominated by large concentration fluctuations 1‐3 . This intrinsic noise has been implicated in the random lysis/lysogeny decision of bacteriophage-λ 4 , in the loss of synchrony of circadian clocks 5,6 and in the decrease of precision of cell signals7. We sought to quantitatively investigate the extent to which the occurrence of molecular fluctuations within single cells (biochemical noise) could explain the variation of gene expression levels between cells in a genetically identical population (phenotypic noise). We have isolated the biochemical contribution to phenotypic noise from that of other noise sources by carrying out a series of differential measurements. We varied independently the rates of transcription and translation of a single fluorescent reporter gene in the chromosome of Bacillus subtilis, and we quantitatively measured the resulting changes in the phenotypic noise characteristics. We report that of these two parameters, increased translational efficiency is the predominant source of increased phenotypic noise. This effect is consistent with a stochastic model of gene expression in which proteins are produced in random and sharp bursts. Our results thus provide the first direct experimental evidence of the biochemical origin of phenotypic noise, demonstrating that the level of phenotypic variation in an isogenic population can be regulated by genetic parameters. We selected as our reporter system a single-copy chromosomal gene with an inducible promoter. As an estimated 50‐80% of bacterial genes are transcriptionally regulated 8 , this system typifies the majority of naturally occurring genes, allowing our results to be extended to natural systems. We incorporated a single copy of our reporter, the green fluorescent protein gene (gfp), into the chromosome of B. subtilis. We chose to integrate gfpinto the chromosome itself, rather than in the form of plasmids, as variation in plasmid copy number 9,10 can act as an additional and unwanted source of noise. Transcriptional efficiency was regulated by using an isopropyl-β-D-thiogalactopyranoside (IPTG)‐inducible promoter, Pspac, upstream of gfp, and varying the concentration of IPTG in the growth medium. Translational

We identified a signaling pathway that prevents initiation of sporulation in Bacillus subtilis when replication initiation is impaired. We isolated mutations that allow a replication initiation mutant (dnaA) to sporulate. These mutations affect a small open reading frame, sda, that was overexpressed in replication initiation mutants and appears to be directly regulated by DnaA. Mutations in replication initiation genes inhibit the onset of sporulation by preventing activation of a transcription factor required for sporulation, Spo0A. Deletion of sda restored activation of Spo0A in replication initiation mutants. Overexpression of sda in otherwise wild-type cells inhibited activation of Spo0A and sporulation. Purified Sda inhibited a histidine kinase needed for activation of Spo0A. Our results indicate that control of sda by DnaA establishes a checkpoint that inhibits activation of Spo0A and prevents futile attempts to initiate sporulation.

Many circular genomes have replication termination systems, yet disruption of these systems does not cause an obvious defect in growth or viability. We have found that the replication termination system of Bacillus subtilis contributes to accurate chromosome partitioning. Partitioning of the terminus region requires that chromosome dimers, that have formed as a result of RecA-mediated homologous recombination, be resolved to monomers by the site-specific recombinase encoded by ripX. In addition, the chromosome must be cleared from the region of formation of the division septum. This process is facilitated by the spoIIIE gene product which is required for movement of a chromosome out of the way of the division septum during sporulation. We found that deletion of rtp, which encodes the replication termination protein, in combination with mutations in ripX or spoIIIE, led to an increase in production of anucleate cells. This increase in production of anucleate cells depended on recA, indicating that there is probably an increase in chromosome dimer formation in the absence of the replication termination system. Our results also indicate that SpoIIIE probably enhances the function of the RipX recombinase system. We also determined the subcellular location of the replication termination protein and found that it is a good marker for the position of the chromosome terminus.

The competence and sporulation factor (CSF) of Bacillus subtilis is an extracellular pentapeptide produced from the product of phrC . CSF has at least three activities: (i) at low concentrations, it stimulates expression of genes activated by the transcription factor ComA; at higher concentrations, it (ii) inhibits expression of those same genes and (iii) stimulates sporulation. Because the activities of CSF are concentration dependent, we measured the amount of extracellular CSF produced by cells. We found that by mid-exponential phase, CSF accumulated to concentrations (1 to 5 nM) that stimulate ComA-dependent gene expression. Upon entry into stationary phase, CSF reached 50 to 100 nM, concentrations that stimulate sporulation and inhibit ComA-dependent gene expression. Transcription of phrC was found to be controlled by two promoters: P1, which precedes rapC , the gene upstream of phrC ; and P2, which directs transcription of phrC only. Both RapC and CSF were found to be part of autoregulatory loops that affect transcription from P1, which we show is activated by ComA∼P. RapC negatively regulates its own expression, presumably due to its ability to inhibit accumulation of ComA∼P. CSF positively regulates its own expression, presumably due to its ability to inhibit RapC activity. Transcription from P2, which is controlled by the alternate sigma factor ς H , increased as cells entered stationary phase, contributing to the increase in extracellular CSF at this time. In addition to controlling transcription of phrC , ς H appears to control expression of at least one other gene required for production of CSF.

Initiation of spore formation in Bacillus subtilis appears to depend on initiation of DNA replication. This regulation was first identified using a temperature-sensitive mutation in dnaB . We found that mutations in the replication initiation genes dnaA and dnaD also inhibit sporulation, indicating that inhibition of sporulation is triggered by general defects in the function of replication initiation proteins.

During the bacterial cell cycle, the tubulin-like cell-division protein FtsZ polymerizes into a ring structure that establishes the location of the nascent division site. We have identified a regulator of FtsZ ring formation in Bacillus subtilis . This protein, EzrA, modulates the frequency and position of FtsZ ring formation. The loss of ezrA resulted in cells with multiple FtsZ rings located at polar as well as medial sites. Moreover, the critical concentration of FtsZ required for ring formation was lower in ezrA null mutants than in wild-type cells. EzrA was associated with the cell membrane and also colocalized with FtsZ to the nascent septal site. We propose that EzrA interacts either with FtsZ or with one of its binding partners to promote depolymerization.