Human G(olf) gene polymorphisms and vulnerability to bipolar disorder

Folding of Gα Subunits: Implications for Disease States

G-proteins play a central role in signal transduction by fluctuating between "on" and "off" phases that are determined by a conformational change. cAMP is a secondary messenger whose formation is inhibited or stimulated by activated G_iα1 or G_sα subunit. We used tryptophan fluorescence, UV/vis spectrophotometry, and circular dichroism to probe distinct structural features within active and inactive conformations from wild-type and tryptophan mutants of G_iα1 and G_sα. For all proteins studied, we found that the active conformations were more stable than the inactive conformations, and upon refolding from higher temperatures, activated wild-type subunits recovered significantly more native structure. We also observed that the wild-type subunits partially regained the ability to bind nucleotide. The increased compactness observed upon activation was consistent with the calculated decrease in solvent accessible surface area for wild-type G_iα1. We found that as the temperature increased, G_α subunits, which are known to be rich in α-helices, converted to proteins with increased content of β-sheets and random coil. For active conformations from wild-type and tryptophan mutants of G_iα1, melting temperatures indicated that denaturation starts around hydrophobic tryptophan microenvironments and then radiates toward tyrosine residues at the surface, followed by alteration of the secondary structure. For G_sα, however, disruption of secondary structure preceded unfolding around tyrosine residues. In the active conformations, a π-cation interaction between essential arginine and tryptophan residues, which was characterized by a fluorescence-measured red shift and modeled by molecular dynamics, was also shown to be a contributor to the stability of G_α subunits. The folding properties of G_α subunits reported here are discussed in the context of diseases associated to G-proteins.

Olfactory Receptors in Non-Chemosensory Organs: The Nervous System in Health and Disease

Olfactory receptors (ORs) and down-stream functional signaling molecules adenylyl cyclase 3 (AC3), olfactory G protein α subunit (Gαolf), OR transporters receptor transporter proteins 1 and 2 (RTP1 and RTP2), receptor expression enhancing protein 1 (REEP1), and UDP-glucuronosyltransferases (UGTs) are expressed in neurons of the human and murine central nervous system (CNS). In vitro studies have shown that these receptors react to external stimuli and therefore are equipped to be functional. However, ORs are not directly related to the detection of odors. Several molecules delivered from the blood, cerebrospinal fluid, neighboring local neurons and glial cells, distant cells through the extracellular space, and the cells’ own self-regulating internal homeostasis can be postulated as possible ligands. Moreover, a single neuron outside the olfactory epithelium expresses more than one receptor, and the mechanism of transcriptional regulation may be different in olfactory epithelia and brain neurons. OR gene expression is altered in several neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), progressive supranuclear palsy (PSP) and sporadic Creutzfeldt-Jakob disease (sCJD) subtypes MM1 and VV2 with disease-, region- and subtype-specific patterns. Altered gene expression is also observed in the prefrontal cortex in schizophrenia with a major but not total influence of chlorpromazine treatment. Preliminary parallel observations have also shown the presence of taste receptors (TASRs), mainly of the bitter taste family, in the mammalian brain, whose function is not related to taste. TASRs in brain are also abnormally regulated in neurodegenerative diseases. These seminal observations point to the need for further studies on ORs and TASRs chemoreceptors in the mammalian brain.

Genetics in dystonia: an update

The past year has been extremely successful with regard to the genetics of dystonia, with the identification of four new dystonia genes (CIZ1, ANO3, GNAL, and TUBB4A). This progress was primarily achieved because of the application of a new technology, next-generation DNA sequencing, which allows rapid and comprehensive assessment of a patient's genome. In addition, a combination of next-generation and traditional Sanger sequencing has expanded the phenotypic spectrum associated with some of the dystonia plus (ATP1A3) and paroxysmal (PRRT2) loci. This article reviews the newly identified genes and phenotypes and discusses the future applications of next-generation sequencing to dystonia research.

Identification of a specific assembly of the g protein golf as a critical and regulated module of dopamine and adenosine-activated cAMP pathways in the striatum

In the principal neurons of striatum (medium spiny neurons, MSNs), cAMP pathway is primarily activated through the stimulation of dopamine D1 and adenosine A_2A receptors, these receptors being mainly expressed in striatonigral and striatopallidal MSNs, respectively. Since cAMP signaling pathway could be altered in various physiological and pathological circumstances, including drug addiction and Parkinson’s disease, it is of crucial importance to identify the molecular components involved in the activation of this pathway. In MSNs, cAMP pathway activation is not dependent on the classical Gs GTP-binding protein but requires a specific G protein subunit heterotrimer containing Gαolf/β2/γ7 in particular association with adenylyl cyclase type 5. This assembly forms an authentic functional signaling unit since loss of one of its members leads to defects of cAMP pathway activation in response to D1 or A_2A receptor stimulation, inducing dramatic impairments of behavioral responses dependent on these receptors. Interestingly, D1 receptor (D1R)-dependent cAMP signaling is modulated by the neuronal levels of Gαolf, indicating that Gαolf represents the rate-limiting step in this signaling cascade and could constitute a critical element for regulation of D1R responses. In both Parkinsonian patients and several animal models of Parkinson’s disease, the lesion of dopamine neurons produces a prolonged elevation of Gαolf levels. This observation gives an explanation for the cAMP pathway hypersensitivity to D1R stimulation, occurring despite an unaltered D1R density. In conclusion, alterations in the highly specialized assembly of Gαolf/β2/γ7 subunits can happen in pathological conditions, such as Parkinson’s disease, and it could have important functional consequences in relation to changes in D1R signaling in the striatum.

Association analysis between polymorphisms in the myo-inositol monophosphatase 2 (IMPA2) gene and bipolar disorder

Linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The myo-inositol monophosphatase 2 gene (IMPA2) maps to this genomic region. Myo-inositol monophosphatase dephosphorylates inositol monophosphate, regenerating free inositol. Lithium, a common treatment for BPD, has been shown to inhibit IMPA2 activity and decrease levels of inositol. It is hypothesized that lithium conveys its therapeutic effect for BPD patients partially through inositol regulation. Hence, dysfunction of inositol caused by IMPA2 irregularity may contribute to the pathophysiology of BPD. In this study, we hypothesize that genetic variations in the IMPA2 gene contributes to increased susceptibility to BPD. We tested this hypothesis by genotyping 9 SNPs (rs1787984; rs585247; rs3974759; rs650727; rs589247; rs669838; rs636173; rs3786285; rs613993) in BPD patients (n=556) and controls (n=735). Genotype and allele frequencies were compared between groups using Chi square contingency analysis. Linkage disequilibrium (LD) between markers was calculated and estimated haplotype frequencies were compared between groups. Single marker analysis revealed several associations between IMPA2 variations and BPD, which were subsequently rendered non-significant after correction for multiple testing. Although our study did not show strong support for an association between the tested IMPA2 polymorphisms and susceptibility to BPD, additional larger studies are necessary to comprehensively investigate a role of the IMPA2 gene in the pathophysiology of BPD.

Association between polymorphisms in the metallophosphoesterase (MPPE1) gene and bipolar disorder

Genetic linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The metallophosphoesterase (MPPE1) gene maps to this region. Dysregulation of protein phosphorylation and subsequent abnormal cellular signaling has been postulated to be involved in neuropsychiatric disorders thus making MPPE1 a plausible biological candidate gene for BPD. In this study, we hypothesized that genetic variation in the MPPE1 gene contributes to BPD. We tested this hypothesis by genotyping four SNPs (rs871044; rs3974590; rs593713; rs602201) in BPD patients (n = 570) and healthy controls (n = 725). Genotypes and allele frequencies were compared between groups using Chi square contingency analysis. Linkage disequilibrium (LD) between markers was calculated and estimated haplotype frequencies were compared between groups. Single marker analysis revealed an association of rs3974590 with BPD (P = 0.009; permutation corrected P = 0.046). Haplotype analysis did not show any significant association with disease after permutation correction. Our results provide evidence of an association between a polymorphism in the MPPE1 gene and BPD. Additional studies are necessary to confirm and elucidate the role of MPPE1 as a susceptibility gene for BPD on chromosome 18p.

Subcellular localization of a novel G protein XLGalpha(olf)

XLGalpha(olf) was identified as a transcriptional variant of the heterotrimeric G protein, Galpha(olf). Previous work showed that XLGalpha(olf) couples with adenosine A2a receptor and dopamine D1 receptor in vitro. However, physiological functions of XLGalpha(olf) remain to be elucidated. In this study, we performed indirect immunofluorescence confocal analyses to examine the subcellular localization of XLGalpha(olf). With overexpression, surprisingly, many large endosomes resulted. We also observed that XLGalpha(olf) localizes at the Golgi apparatus. The N-terminal region of XLGalpha(olf) appears necessary for both endosome formation and the Golgi localization. The results indicate that XLGalpha(olf) and Galpha(olf) play distinctly separate roles. Moreover, XLGalpha(olf) colocalized with Rab3A and Rab8A, as well as partially with Rab11A, but not with other endocytotic endosomes. We could confirm the interaction between XLGalpha(olf) and Rab3A/Rab8A by co-immunoprecipitation experiments. Our study provides important clues toward understanding physiological functions of XLGalpha(olf).

Association analysis of the pituitary adenylate cyclase-activating polypeptide (PACAP/ADCYAP1) gene in bipolar disorder

BACKGROUND

Linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The pituitary adenylate cyclase-activating polypeptide/adenylate cyclase-activating polypeptide 1 (pituitary) (PACAP/ADCYAP1) gene maps to this region. PACAP is a neuropeptide involved in neurotransmission in both the peripheral nervous system and central nervous system and is required for catecholamine secretion. Animal models of PACAP mutations show remarkable behavioral defects, including hyperactivity and increased exploratory behavior.

OBJECTIVE

In this study we tested the hypothesis that genetic variations in the human PACAP gene contribute to BPD.

METHODS

Genotyping of seven single nucleotide polymorphisms (rs1893154; rs2846811; rs8192595; rs2856966; rs928978; rs2231187; rs1610037) was performed in BPD patients (n=570) and healthy controls (n=710). Genotypes and allele frequencies were compared between groups using chi contingency analysis. Linkage disequilibrium between markers was calculated and estimated haplotype frequencies were compared between groups.

MAIN RESULTS

There were no significant differences between groups on the allele, genotype or haplotype level for any of the tested single nucleotide polymorphisms.

CONCLUSION

Our results provide no evidence of an association of the PACAP gene with BPD in this group of patients and controls. Additional studies are necessary to elucidate the BPD susceptibility locus on chromosome 18p.

Suggestive linkage of a chromosomal locus on 18p11 to cyclothymic temperament in bipolar disorder families

Attempts to identify bipolar disorder (BP) genes have only enjoyed limited success. One potential cause for this problem is that the traditional categorical BP phenotypes currently used in genetic linkage studies are not the most informative, efficient, or biologically relevant. An alternative to these strict categorical BP phenotypes is quantitative BP phenotypes. By isolating one aspect of a complex trait such as BP into a simple, intermediate, quantitative trait, genes that contribute to the larger complex trait can be more readily identified. Along these lines, we utilized a temperament-based measure (cyclothymic temperament) as a quantitative, intermediate BP phenotype in linkage analyses and hypothesized that this measure might more efficiently detect loci for BP or temperamental traits that predispose to BP. A total of 158 individuals with temperament data from 28 BP families were used in the linkage analyses. All pedigrees had a proband diagnosed with BPI or BPII and at least two other family members with a mood disorder diagnosis. An 8 cM genome scan was performed and analyzed using MERLIN nonparametric multipoint regression linkage for a cyclothymic temperament trait. The highest overall LOD score was on chromosome 18 (LOD = 2.71, P = 0.0002). Other linkage peaks which may indicate potential regions of interest were found on chromosomes 3 and 7. The temperament-based cyclothymic trait yielded a higher peak LOD score and a lower P-value than analyses using traditional, categorical phenotypes in a separate analysis including these same families.

Investigation of the G protein subunit Galphaolf gene (GNAL) in attention deficit/hyperactivity disorder

The dopamine system plays an important role in the regulation of attention and motor behavior, subsequently, several dopamine-related genes have been associated with Attention Deficit/Hyperactivity Disorder (ADHD). Among them are the dopamine receptors D1 and D5 that mediate adenylyl cyclase activation through coupling with G(s)-like proteins. We thus hypothesized that the G(s)-like subunit Galpha(olf), expressed in D1-rich areas of the brain, contributes to the genetic susceptibility of ADHD. To evaluate the involvement of the Galpha(olf) gene, GNAL, in ADHD, we examined the inheritance pattern of 12 GNAL polymorphisms in 258 nuclear families ascertained through a proband with ADHD (311 affected children) using the transmission/disequilibrium test (TDT). Categorical analysis of individual marker alleles demonstrated biased transmission of one polymorphism in GNAL intron 3 (rs2161961; P=0.011). We also observed significant relationships between rs2161961 and dimensional symptoms of inattention and hyperactivity/impulsivity (P=0.003 and P=0.008). In addition, because of recent evidence of imprinting at the GNAL locus, secondary analyses were split into maternal and paternal transmissions to assess a contribution of parental effects. We found evidence of strong maternal effect, with preferential transmission of maternal alleles for rs2161961A (P=0.005) and rs8098539A (P=0.035). These preliminary findings suggest a possible contribution of GNAL in the susceptibility to ADHD, with possible involvement of parent-of-origin effects.

Phosducin-like protein levels in leukocytes of patients with major depression and in rat cortex: the effect of chronic treatment with antidepressants

The importance of signal transduction processes beyond receptors involving receptor-G protein coupling, in both the pathophysiology and the treatment of mood disorders, is well documented. Thus, regulatory elements of G protein function may play a role in the molecular mechanisms underlying these alterations. Phosducin-like proteins, a family of regulators of G protein function expressed throughout brain and body, modulate G protein function by high affinity sequestration of G protein-betagamma subunits, thus impeding G protein-mediated signal transmission by both Galpha and Gbetagamma subunits. An important consequence of Gbetagamma neutralization is the prevention of G protein-coupled receptor kinase phosphorylation resulting in a temporary protection to agonist-bound receptor desensitization. Phosducin-like protein levels were measured in brain cortices of rats chronically treated with one of five classes of antidepressants: imipramine, venlafaxine, maprotiline, citalopram, and moclobemide. None of the antidepressant treatments had any significant effect on phosducin-like protein levels. Phosducin-like protein levels were evaluated in mononuclear leukocytes from a group of 15 patients diagnosed with major depressive episode, both before the initiation of antidepressant treatment and after 4 weeks of antidepressant medication. No protein changes were found in leukocytes of either untreated patients with major depressive disorder or after 4 weeks of the treatment in comparison with healthy volunteers.

The involvement of G proteins and regulators of receptor-G protein coupling in the pathophysiology, diagnosis and treatment of mood disorders

Biochemical research in mood disorders has focused, along the cascade of events involved in signal transduction, from studies at the level of the monoamine neurotransmitter to the level of the neurotransmitter receptors, and lately to information transduction mechanisms beyond receptors, involving the coupling of receptors with signal transducers. We review findings concerning (a) the involvement of G proteins, in the pathophysiology, diagnosis and treatment of mood disorders; (b) the importance of regulation of receptor-G protein coupling, G protein-coupled receptor kinases (GRKs), beta-arrestins, to the pathophysiology of mood disorders and the mechanism of action of antidepressants. We relate to the special complexity of mental disorders with regards to etiology and pathophysiological diagnosis as well as to the strength and limitations of the 'pharmacological bridge' approach governing studies to unravel the etiology of mental disorders. There are presently no established and reliable, sensitive and specific objective biological diagnostic markers in psychiatry that can serve as 'gold standards'. The future achievement of an objective biochemical differential diagnostic system for major mental disorders that will also enable an objective biological treatment monitoring is expected to be revolutionary for psychiatry with a magnitude similar to the impact of the discovery of psychopharmacological treatments for mental disorders more than 50 years ago.

Lack of association between variations in the melanocortin 5 receptor gene and bipolar disorder

OBJECTIVE

The melanocortin 5 receptor gene maps to the bipolar susceptibility locus on chromosome 18p11.2. Given the biological role of melanocortins and their influence on the hypothalamic-pituitary-adrenal axis, the melanocortin 5 receptor gene is a plausible candidate gene for bipolar disorder. We tested the hypothesis that the potential functional variation Phe209Leu confers susceptibility to bipolar disorder in a case-control study.

METHODS

Genotypes for two variations in the coding region and one variation approximately 7 kb upstream from the coding region were obtained from 345 unrelated bipolar I patients and 275 control samples. Genotypes and allele frequencies were compared between groups using chi(2) contingency analysis.

RESULTS

Allele frequencies of the Phe209Leu polymorphism did not differ significantly between bipolar patients and controls (P=0.679). Allele frequencies of the C744T and the intergenic A/G polymorphism did not differ significantly between bipolar patients and controls. All variations were in strong linkage disequilibrium.

CONCLUSION

Variations in the melanocortin 5 receptor gene are unlikely to confer susceptibility to bipolar disorder in this sample. Further studies are required to elucidate the susceptibility locus for bipolar disorder on chromosome 18p11.

Association analysis of CHMP1.5 genetic variation and bipolar disorder

OBJECTIVES

The18p11.2 region surrounding the G-olf gene has been linked in several independent studies to bipolar disorder and schizophrenia, yet association studies between G-olf genetic variations and bipolar disorder have been negative. We hypothesized that the linkage in this region might be due to a gene in close physical proximity to G-olf, and we examined variations in the CHMP1.5 gene within intron 5 of G-olf for association with bipolar disorder.

METHODS

Two single-nucleotide polymorphisms, rs1786581 and rs1249624, were analyzed for association with bipolar disorder in 402 unrelated bipolar individuals and 181 unrelated controls. Genotyping was performed via pyrosequencing and restriction fragment length polymorphism analysis; results were compared by chi2 contingency analysis.

RESULTS

No evidence was found for association of either allele at rs1249624 with bipolar disorder (chi2=1.25, degrees of freedom=1, P=0.26); however, a trend towards association with the 'T' allele at rs1786581 and with the 'T/T' 1786581/1249624 haplotype was observed. The chi2 for the haplotype was 7.16, (degrees of freedom=3, P=0.067) and for rs1786581 chi2=3.56, degrees of freedom=1, P=0.060; these differences are not statistically significant.

CONCLUSIONS

Variation in the CHMP1.5 gene does not appear to be associated with bipolar disorder. A systematic assessment of genetic variation in the region using association studies will be necessary.

Alternative transcripts and evidence of imprinting of GNAL on 18p11.2

Genetic studies implicating the region of human chromosome 18p11.2 in susceptibility to bipolar disorder and schizophrenia have observed parent-of-origin effects that may be explained by genomic imprinting. We have identified a transcriptional variant of the GNAL gene in this region, employing an alternative first exon that is 5' to the originally identified start site. This alternative GNAL transcript encodes a longer functional variant of the stimulatory G-protein alpha subunit, Golf. The isoforms of Golf display different expression patterns in the CNS and functionally couple to the dopamine D1 receptor when heterologously expressed in Sf9 cells. In addition, there are CpG islands in the vicinity of both first exons that are differentially methylated, a hallmark of genomic imprinting. These results suggest that GNAL, and possibly other genes in the region, is subject to epigenetic regulation and strengthen the case for a susceptibility gene in this region.

Insertion/deletion polymorphism in clusterin gene influences serum lipid levels and carotid intima-media thickness in hypertensive Japanese females

Clusterin has been implicated in lipid metabolism and atherogenesis, however, the influence of genetic variation has not been examined in Japanese. In this study, we identified 11 single nucleotide polymorphisms (SNPs) of clusterin gene by direct sequencing. Among them, one promoter SNP (-4453T>G), one missense SNP (4183G>A), and 2 common SNPs (5608T>C and 6316delT) were genotyped in 525 asymptomatic hypertensives not treated with lipid lowering agents. -4453T>G, 4183G>A, and 5608T>C showed no correlation with the clinical characteristics, however, in the 6316delT, an insertion (I)/deletion (D) polymorphism, D/D subjects had significantly higher levels of total cholesterol and low-density lipoprotein (LDL)-cholesterol than I/I subjects in females but not in males. Female subjects with the D allele (D/D+I/D) had greater intima-media thickness of the carotid artery than I/I subjects. In a multiple logistic regression analysis, the D allele of 6316delT was detected as an independent predictor for the plaque prevalence. In conclusion, the clusterin gene polymorphism may contribute to the serum lipid levels and the progression of carotid atherosclerosis in hypertensive Japanese females.

No association between common variations in the human alpha 2 subunit gene (ATP1A2) of the sodium–potassium-transporting ATPase and idiopathic generalized epilepsy

Quantitative trait loci studies in inbred mice have identified a locus on chromosome 1 (Szs1) of fundamental importance to seizure susceptibility. High-ranking candidate genes in this susceptibility region include KCNJ9, KCNJ10 and ATP1A2. We performed a systematic mutation scan of the coding region of the human ATP1A2 gene and performed a case-control association study with seven common markers. Genotypes were assessed in 152 idiopathic generalized epilepsy (IGE) patients of German ancestry and 111 healthy German controls for all seven polymorphisms. No significant differences were found in genotype or allele frequencies for any of the variations between the IGE patients and controls. No haplotypes were associated with IGE when compared to controls. Linkage disequilibrium was demonstrated throughout the gene. Results suggest that the polymorphisms we studied in the ATP1A2 gene do not represent major susceptibility factors for common forms of IGE.

Analysis of polymorphisms in the alpha-subunit of the olfactory G-protein Golf in lithium-treated bipolar patients

OBJECTIVE

This study examines the alpha-subunit of the olfactory G-protein (G(olf)) as a possible candidate gene for bipolar disorder. The alpha-subunit of the G(olf) gene maps to a region on chromosome 18p that has been implicated in several linkage studies as a potential site of a bipolar disorder susceptibility loci.

METHODS

We investigated whether two polymorphisms in the alpha-subunit of the G(olf) gene (A-->G in intron 3 and T-->G in intron 10) are associated with bipolar disorder in a sample of 149 bipolar patients under lithium treatment compared with 139 healthy controls using haplotype analysis.

RESULTS

There was no evidence for an association between the investigated polymorphisms in the G(olf) gene and bipolar disorders, as well as to response to lithium treatment or common side effects, like hand tremor, weight gain and cognitive dysfunction.

CONCLUSION

The results of the present study do not support the hypothesis that the G(olf) gene is a major susceptibility factor for bipolar disorders.

Linkage analysis in psychiatric disorders: the emerging picture

Gene finding in genetically complex diseases has been difficult as a result of many factors that have diagnostic and methodologic considerations. For bipolar disorder and schizophrenia, numerous family, twin, and adoption studies have identified a strong genetic component to these behavioral psychiatric disorders. Despite difficulties that include diagnostic differences between sample populations and the lack of statistical significance in many individual studies, several promising patterns have emerged, suggesting that true susceptibility loci for schizophrenia and bipolar disorder may have been identified. In this review, the genetic epidemiology of these disorders is covered as well as linkage findings on chromosomes 4, 12, 13, 18, 21, and 22 in bipolar disorder and on chromosomes 1, 6, 8, 10, 13, 15, and 22 in schizophrenia. The sequencing of the human genome and identification of numerous single nucleotide polymorphisms (SNP) should substantially enhance the ability of investigators to identify disease-causing genes in these areas of the genome.

Toward molecular diagnostics of mood disorders in psychiatry

Mental disorders are highly prevalent and often difficult to diagnose. There is a significant gap between advances in their pharmacotherapy and the present lack of objective biologic tests for diagnosis. The special complexity of diagnosis in psychiatry is related to the absence of objective diagnostic "gold standards", co-morbidity, heterogeneity and equifinality, quantitative trait loci, and locus heterogeneity. Here, we review recent findings relating to diagnostic, pathophysiological, and linkage markers for mood disorders at the biochemical level involving monoamine neurotransmitters, hormones, and signal-transducing G proteins. Identification of biological diagnostic markers could enable segregating mood disorders to several biologically different subtypes. New-era methods and strategies involving genomics, proteomics, multi-marker approach and single nucleotide polymorphisms have the potential to revolutionize future diagnosis in psychiatry.

Analysis of polymorphisms in the olfactory G-protein Golf in major depression

It is well established that G-proteins represent essential regulatory components in transmembrane signaling. The alpha subunit of the olfactory G-protein Golf (GNAL) maps to a region on chromosome 18 where linkage to affective disorders has been reported, as well as a parent-of-origin effect in affective disorders with some markers near the locus for the alpha subunit of the Golf gene. We investigated whether two polymorphisms in the alpha subunit of the Golf gene (A-->G in intron 3, and T-->G in intron 10) are associated with major depression in 176 major depressive patients compared with 145 healthy control subjects, and additionally tested for a parent-of-origin effect in separated gender groups. In the control group, we found a significant increase in the G-allele frequency of the intron 3 polymorphism in females (P=0.0036, odds ratio=2.13, 95% confidence interval=1.29-3.54, Fisher's Exact Test). In patients, we found a similar tendency for higher G-allele frequencies in females. Concerning the intron 10 polymorphism, no differences in the genotype or allele frequencies were detectable for any of the separated gender groups. Also, the total patient and control groups showed no differences in allele or genotype frequencies for any of the investigated polymorphisms. The results of this study agree with the reported parent-of-origin effects on chromosome 18, but do not support the hypothesis that the Golf gene is a major susceptibility factor for major depression.

Activation of adenylyl cyclases, regulation of insulin status, and cell survival by G(alpha)olf in pancreatic beta-cells

Because we recently identified the G(alpha)olf subunit in rat pancreatic beta-cells, we investigated the downstream effectors and the biological functions of this G protein in HEK-293T cells and the insulin-secreting mouse betaTC-3 cell line. With the use of transient transfection of HEK-293T cells with constitutively activated G(alpha)olf (G(alpha)olfQ214L, i.e., AG(alpha)olf), together with expression vectors encoding the adenylyl cyclase (AC) isoforms (AC-I to -VIII and soluble AC), compared with cotransfections using AG(alphas) (G(alphas)R201C), we observed that AG(alpha)olf preferentially activates AC-I and -VIII, which are also expressed in beta-cells. Stable overexpression of wild-type or AG(alpha)olf in betaTC-3 cells resulted in partial attenuation of insulin secretion and biosynthesis, suggesting that chronic activation of the G(alpha)olf-signaling pathway is associated with beta-cell desensitization. In agreement, transfected betaTC-3 cells present a decreased insulin content with respect to parental cells, whereas the proinsulin convertases PC-1 and PC-2 were unaffected. Furthermore, betaTC-3-AG(alpha)olf cells are resistant to serum starvation-induced apoptosis. Our findings suggest that G(alpha)olf is involved in insulin status, cell survival, and regeneration of the insulin-secreting beta-cells during development and diabetes.

Molecular genetics of bipolar disorder

Alteration of monoaminergic neurotransmission is implicated in the pathophysiology of bipolar disorder (manic-depressive illness). Candidate genes participating in monoaminergic neurotransmission, especially serotonin transporter and monoamine oxidase A, may be associated with bipolar disorder. And the regulating regions of these genes and the molecules participating in intracellular signal transduction are now under investigation. To date, 13 whole genome positional cloning studies have been performed and many candidate loci identified. Using patients from a pedigree in which schizophrenia, depression or bipolar disorder have been linked with a balanced translocation at 1 and 11, candidate pathogenetic genes were cloned as DISC1 (disrupted in schizophrenia-1) and DISC2. Recently, pathogenetic mutations have been identified in two genetic diseases frequently co-morbid with mood disorder; WFS1 for Wolfram syndrome and ATP2A2 (SERCA2) for Darier's disease. Transmission of bipolar disorder may be characterized by anticipation and parent-of-origin effect, and extended CTG repeat at SEF2-1B gene was identified from a bipolar patient. However, its pathogenetic role was not supported by subsequent studies. Association of bipolar disorder with mitochondrial DNA has also been suggested. The role of genomic imprinting is also possible because linkage to 18p11 is limited to paternally transmitted pedigrees. These results warrant further study of molecular genetics of bipolar disorder.

Implications of the cAMP signaling pathway in psychiatric disorders: a systematic review of the evidence

The last decade has seen a shift in the theoretical framework addressing the pathophysiology of psychiatric disorders. During this period, research endeavors have been directed toward investigating the biochemical mechanisms involved in the transduction of information from the cell surface to the cell interior. The emerging picture, supported by growing evidence, is that in addition to neurotransmitters and their receptors, various signal transduction pathways may be linked to the pathophysiology of major psychiatric disorders. In this review, the role of one such pathway--the cyclic adenosine monophosphate (cAMP) signaling pathway--will be highlighted. We review data suggesting the involvement of the upstream and downstream components of this system in the pathophysiology of psychiatric disorders.

Sequence and genomic organization of the human G-protein Golfalpha gene (GNAL) on chromosome 18p11, a susceptibility region for bipolar disorder and schizophrenia

The sequence and genomic organization of the human Golfalpha (GNAL) gene were determined. The human GNAL gene was found to contain 12 coding exons, and it spans over 80 kb on chromosome 18p11. 5' RACE analysis suggested an additional transcription initiation start site. Sequence analysis of the putative promoter region revealed conserved binding sites for several transcription factors. Sequence analysis of the 3'-untranslated region revealed the presence of two Alu sequences and two polyadenylation signals. 3' RACE analysis confirmed the functionality of the most downstream poly-a signal. The human GNAL was found to be expressed as a single transcript of about 5.9 kb in the brain. One highly informative dinucleotide repeat was found in intron 5. Additionally, a processed pseudogene for asparagine synthetase was found about 6 kb upstream of the GNAL gene. Knowledge of the sequence and structure of the human GNAL gene provides essential information for further analysis of the GNAL locus at chromosome 18p11 which has been linked to bipolar disorder and schizophrenia.

Identification of candidate genes for psychiatric disorders on 18p11

Linkage studies have suggested a locus for bipolar disorder as well as schizophrenia in the pericentric region of chromosome 18. Several candidate genes have been identified in the region including ACTH, IMP, and G(olf), however no reports of mutations in families showing linkage to the 18p11 locus have been reported. Recently, mild linkage disequilibrium has been observed with a polymorphic marker that maps within the G(olf) gene and schizophrenia in families from Germany and Israel, suggesting that a gene mapping near G(olf) may be involved in psychiatric disorders. A BAC and cosmid contig around the G(olf) locus has been generated and BAC clones were used for cDNA selection experiments. Several novel genes have been identified which are expressed in the brain. These genes may be possible candidate genes for psychiatric illness.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Genetics of bipolar affective disorder

Bipolar affective disorder is a highly heritable condition, as demonstrated in twin, family, and adoption studies. Morbid risk in first degree relatives is four to six times higher than the population prevalence of about 1%. However, the mode of inheritance is complex, and linkage findings have been difficult to replicate. Despite these limitations, consistent linkage findings have emerged on several chromosomes, notably 18p, 18q, 21q, 12q, 4p, and Xq. Two additional areas, 10p and 13q, have shown linkage in regions that appear to overlap with significant linkage findings in schizophrenia. Separate linkage studies in schizophrenia also have targeted the replicated bipolar linkages on 18p and 22q. New methods are being developed for fine mapping and candidate identification. Recent candidate gene studies include some positive results for the serotonin transporter gene on 17q and the catechol-o-methyltransferase gene on 22q. No other candidate gene studies are yet showing replicated results. A convincing demonstration for a susceptibility gene will probably require a mixture of case- control studies, family-based association methods, and pathophysiologic studies.

The role of G proteins in the psychobiology and treatment of affective disorders and their integration with the neurotransmitter hypothesis

Heterotrimeric G proteins are a crucial point of convergence in the transmission of signals from a variety of primary messengers and their membrane receptors to downstream intracellular second messenger effector enzymes and ionic channels. Thus, these proteins have raised increasing interest in the clinical perspective of altered G protein function. This article addresses the most recent significant findings regarding the role of G proteins in the pathophysiology of mood disorders and in the molecular mechanisms underlying the treatment of these disorders, with emphasis on biochemical and genetic approaches.

Do schizophrenia and affective disorder share susceptibility genes?

Schizophrenia and affective disorders are relatively common neuropsychiatric diseases with a complex genetic etiology. A multigenic inheritance with variable influence of unknown environmental factors may be involved. Family studies have demonstrated the existence of both phenotypes in the same kindreds, and in certain cases, a transition from one phenotype to another occurs. In addition, intermediate phenotypes such as schizoaffective disorders are found in families with schizophrenia and affective illness. Recent genome and chromosomal scans appear to support these epidemiologic data, since susceptibility regions for both schizophrenia and affective disorders have been found to overlap, on chromosomes 10p13-p12, 13q32, 18p and 22q11-q13. These studies were performed in independently ascertained family samples with index patients afflicted either with schizophrenia or bipolar disorder. Taken together, these findings imply shared loci for schizophrenia and affective disorders among those required for the full expression of the phenotype. Identification and molecular characterization of the genetic components conferring risk to both disorders would impact positively on diagnosis, prevention, and treatment.