Identification and characterization of a tandem repeat in exon III of the dopamine receptor D4 (DRD4) gene in cetaceans

A large number of mammalian species harbor a tandem repeat in exon III of the gene encoding dopamine receptor D4 (DRD4), a receptor associated with cognitive functions. In this study, a DRD4 gene exon III tandem repeat from the order Cetacea was identified and characterized. Included in our study were samples from 10 white-beaked dolphins (Lagenorhynchus albirostris), 10 harbor porpoises (Phocoena phocoena), eight sperm whales (Physeter macrocephalus), and five minke whales (Balaenoptera acutorostrata). Using enzymatic amplification followed by sequencing of amplified fragments, a tandem repeat composed of 18-bp basic units was detected in all of these species. The tandem repeats in white-beaked dolphin and harbor porpoise were both monomorphic and consisted of 11 and 12 basic units, respectively. In contrast, the sperm whale harbored a polymorphic tandem repeat with size variants composed of three, four, and five basic units. Also the tandem repeat in minke whale was polymorphic; size variants composed of 6 or 11 basic units were found in this species. The consensus sequences of the basic units were identical in the closely related white-beaked dolphin and harbor porpoise, and these sequences differed by a maximum of two changes when compared to the remaining species. There was a high degree of similarity between the cetacean basic unit consensus sequences and those from members of the horse family and domestic cow, which also harbor a tandem repeat composed of 18-bp basic units in exon III of their DRD4 gene. Consequently, the 18-bp tandem repeat appears to have originated prior to the differentiation of hoofed mammals into odd-toed and even-toed ungulates. The composition of the tandem repeat in cetaceans differed markedly from that in primates, which is composed of 48-bp repeat basic units.     

Origin and divergence of tandem repeats of primate D4 dopamine receptor genes

Human D4 dopamine receptor (D4DR) is polymorphic in terms of the repeat, numbers of the 48-base pairs (bp) sequence located in the third cytoplasmic loop of the receptor. The repeated sequence and its polymorphism in D4DR genes have also been identified in higher non-human primates, suggesting that the structure of D4DR has been maintained during primate evolution. To clarify the origin and divergence of the polymorphism in the D4DR gene, we determined the nucleotide sequence of this region of the D4DR gene in several species of prosimians and the tree shrew, a species which is closely related to primates. Prosimians except the tarsier had one or two unit(s) of the 48-bp sequence, and conserved sequences were recognized in most of the units of the prosimians. The tree shrew had only one unit of the 48-bp sequence, and its sequence was 71–75% identical to those of the nuits of galago, loris, and lemur. These findings suggest that the ancestral primate presumably had one 48-bp unit, and duplication of the unit occurred at the stage of prosimians. Tarsiers appeared to be distinct from other prosimians and simians because of the high repeat numbers of units and their sequences.     

Evolution of exon 1 of the dopamine D4 receptor (DRD4) gene in primates

The dopamine D4 receptor (DRD4) gene exhibits a large amount of expressed polymorphism in humans. To understand the evolutionary history of the first exon of DRD4-which in humans contains a polymorphic 12bp tandem duplication, a polymorphic 13bp deletion, and other rare variants-we examined the homologous exon in thirteen other primate species. The great apes possess a variable number of tandem repeats in the same region as humans, both within and among species. In this sense, the 12bp tandem repeat of exon 1 is similar to the 48bp VNTR of exon 3 of DRD4, previously shown to be polymorphic in all primate species examined. The Old World monkeys show no variation in length, and a much higher conservation of amino acid sequence than great apes and humans. The New World monkeys show interspecific differences in length in the region of the 12bp polymorphism, but otherwise show the higher conservation seen in Old World monkeys. The different patterns of variation in monkeys compared to apes suggest strong purifying selective pressure on the exon in these monkeys, and somewhat different selection, possibly relaxed selection, in the apes.     

Association between the dopamine D4 receptor gene exon III variable number of tandem repeats and political attitudes in female Han Chinese

Twin and family studies suggest that political attitudes are partially determined by an individual''s genotype. The dopamine D4 receptor gene (DRD4) exon III repeat region that has been extensively studied in connection with human behaviour, is a plausible candidate to contribute to individual differences in political attitudes. A first United States study provisionally identified this gene with political attitude along a liberal–conservative axis albeit contingent upon number of friends. In a large sample of 1771 Han Chinese university students in Singapore, we observed a significant main effect of association between the DRD4 exon III variable number of tandem repeats and political attitude. Subjects with two copies of the 4-repeat allele (4R/4R) were significantly more conservative. Our results provided evidence for a role of the DRD4 gene variants in contributing to individual differences in political attitude particularly in females and more generally suggested that associations between individual genes, and neurochemical pathways, contributing to traits relevant to the social sciences can be provisionally identified.     

(G)n-Mononucleotide polymorphism in the human D4 dopamine receptor (DRD4) gene

Polymorphism in intron I of the human dopamine D4 receptor is described.     

The genetic architecture of selection at the human dopamine receptor D4 (DRD4) gene locus

Associations of the seven-repeat (7R) allele of the human dopamine receptor D4 (DRD4) gene with both the personality trait of novelty seeking and attention deficit/hyperactivity disorder have been reported. Recently, on the basis of the unusual DNA sequence organization of the DRD4 7R 48-bp tandem repeat (VNTR), we proposed that the 7R allele originated as a rare mutational event that increased to high frequency by positive selection. We now have resequenced the entire DRD4 locus from 103 individuals homozygous for 2R, 4R, or 7R variants of the VNTR, a method developed to directly estimate haplotype diversity. DNA from individuals of African, European, Asian, North and South American, and Pacific Island ancestry were used. 4R/4R homozygotes exhibit little linkage disequilibrium (LD) over the region examined, with more polymorphisms observed in DNA samples from African individuals. In contrast, the evidence for strong LD surrounding the 7R allele is dramatic, with all 7R/7R individuals (including those from Africa) exhibiting the same alleles at most polymorphic sites. By intra-allelic comparison at 18 high-heterozygosity sites spanning the locus, we estimate that the 7R allele arose prior to the upper Paleolithic era (approximately 40000-50000 years ago). Further, the pattern of recombination at these polymorphic sites is the pattern expected for selection acting at the 7R VNTR itself, rather than at an adjacent site. We propose a model for selection at the DRD4 locus consistent with these observed LD patterns and with the known biochemical and physiological differences between receptor variants.     

The D4 dopamine receptor (DRD4) maps to distal 11p close to HRAS.

Dopaminergic pathophysiology is important in several psychiatric illnesses. The recently cloned D4 dopamine receptor gene (DRD4) shows considerable homology to the D2 and D3 dopamine receptors (DRD2 and DRD3); pharmacologically, its affinity for the atypical antipsychotic clozapine is much higher than that of these other dopamine receptors. Probe pB28 for this locus recognizes an informative HincII polymorphism. We typed this polymorphism on several large reference families (a total of about 271 individuals) to place DRD4 in the genetic linkage map. Pairwise linkage analysis (using ILINK) provided evidence for close linkage to the distal 11p loci tyrosine hydroxylase (TH) and the Harvey ras oncogene (HRAS). We used our version of LINKMAP adapted to run under distributed parallel processing (Linda-LINKMAP) for an analysis moving DRD4 across a fixed map with HRAS set 3.8 cM distal to TH. This localized DRD4 close to HRAS, with no crossovers observed between those loci and a maximum lod score of 19.9 (2 cM distal to HRAS). The one LOD unit support interval extends from about 1 cM proximal to HRAS to 8 cM distal to HRAS. Crossovers identified in one kindred place DRD4 distal to TH, providing further evidence for its location close to HRAS, making DRD4 one of the most telomeric of 11p markers. (This also places DRD4 in band 11p15.5.)     

Polymorphism of dopamine receptor D4 exon I corresponding region in chicken

In stockbreeding, there are indications that behavioral traits of livestock have an effect on breeding and production. If the variation in individual behavior is related to that in neurotransmitter-related genes such as in humans, it would be possible to breed pedigrees composed of individuals having behavioral traits that are useful to production and breeding using selection based on genotypes. In this study, we investigated the exon I region of dopamine receptor D4 (DRD4), in which variation is related to psychiatric disorder in humans, in major poultry species namely Japanese quail (Coturnix japonica), chicken (Gallus gallus), ring-necked pheasant (Phasianus colchicus) and helmeted guinea fowl (Numida meleagris). Furthermore, we investigated Japanese cormorant (Phalacrocorax capillatus) and Japanese jungle crow (Corvus macrorhynchos) as an out-group. In these species of birds, the repeat of proline was identified in the region corresponding to the human polymorphic region. The repeat number was 9 in Japanese quail, ring-necked pheasant and Japanese cormorant; 12 in helmeted guinea fowl; and 3 in Japanese jungle crow. However, no polymorphism was found in these species. In contrast, polymorphism was observed in chicken and two alleles with 8 and 9 repeats were identified. Although 9 repeats (allele 9) were predominant in most chicken breeds, Black Minorca had only 8 repeats (allele 8). Intra-breed polymorphism was found in 6 out of 12 breeds, and two alleles (alleles 8 and 9) were detected in these breeds. This polymorphism, which is the first to be reported on a neurotransmitter-related gene in birds, would contribute significant information for elucidation of differences in behavioral traits in chicken breeds.     

Dopamine transporter (DAT1) and dopamine receptor D4 (DRD4) genotypes differentially impact on electrophysiological correlates of error processing

Recent studies as well as theoretical models of error processing assign fundamental importance to the brain's dopaminergic system. Research about how the electrophysiological correlates of error processing--the error-related negativity (ERN) and the error positivity (Pe)--are influenced by variations of common dopaminergic genes, however, is still relatively scarce. In the present study, we therefore investigated whether polymorphisms in the DAT1 gene and in the DRD4 gene, respectively, lead to interindividual differences in these error processing correlates. One hundred sixty participants completed a version of the Eriksen Flanker Task while a 26-channel EEG was recorded. The task was slightly modified in order to increase error rates. During data analysis, participants were split into two groups depending on their DAT1 and their DRD4 genotypes, respectively. ERN and Pe amplitudes after correct responses and after errors as well as difference amplitudes between errors and correct responses were analyzed. We found a differential effect of DAT1 genotype on the Pe difference amplitude but not on the ERN difference amplitude, while the reverse was true for DRD4 genotype. These findings are in line with predictions from theoretical models of dopaminergic transmission in the brain. They furthermore tie results from clinical investigations of disorders impacting on the dopamine system to genetic variations known to be at-risk genotypes.     

Polar alteration of short tandem repeats (STRs) in mammalian cells

Instability of short tandem repeats (STRs) in DNA during replication is observed in all organisms examined, and is causatively involved in various human diseases. We explore the mechanisms involved in instability by examining length changes occurring during the replication of [(CA)(20)TA](n) and [(CAG)(20)TAG](n), in human cells. We show that the majority of alterations consist of an insertion or deletion of one repeat unit, and base substitutions or length changes involving many repeat units are rare. We also show that length changes of two-tract STRs are biased toward the 3'-end of the repeat tract, in reference to lagging strand synthesis. There are some differences between our observations and previous observations in microbes, e.g. the orientation effect was not observed in this study. The results of this study are discussed in terms of the molecular mechanisms leading to alterations in repeat tracts.     

A rare FokI RFLP in the human dopamine D2 receptor gene (DRD2)

Summary A new biallelic polymorphism for FokI restriction enzyme due to CT transition in the fourth intron of human DRD2 is described. It must be a usefull marker of this candidate gene for several mental disorders.     

The 7R polymorphism in the dopamine receptor D4 gene (DRD4) is associated with financial risk taking in men

Individuals exhibit substantial heterogeneity in financial risk aversion. Recent work on twins demonstrated that some variation is influenced by individual heritable differences. Despite this, there has been no study investigating possible genetic loci associated with financial risk taking in healthy individuals. Here, we examined whether there is an association between financial risk preferences, elicited experimentally in a game with real monetary payoffs, and the presence of the 7-repeat allele (7R+) in the dopamine receptor D₄ gene as well as the presence of the A1 allele (A1+) in the dopamine receptor D₂ gene in 94 young men. Although we found no association between the A1 allele and risk preferences, we did find that 7R+ men are significantly more risk loving than 7R? men. This polymorphism accounts for roughly 20% of the heritable variation in financial risk taking. We suggest that selection for the 7R allele may be for a behavioral phenotype associated with risk taking. This is consistent with previous evolutionary explanations suggesting that selection for this allele was for behaviors associated with migration and male competition, both of which entail an element of risk.     

Polymorphism of the dopamine D4 receptor (DRD4) and serotonin transporter (5-HTTL) gene promoter regions in african tribes of Hadza and Datoga

Molecular genetic analysis of the allelic variants of the DRD4 and 5-HTTL gene promoter regions was performed in African tribes of Hadza and Datoga, characterized by different levels of socially acceptable aggression. It was demonstrated that Hadza and Datoga people differed in the structural organization of one of the 5-HTTL alleles (extra long allele xL). Analysis of the allele length polymorphism of both genes showed that in the Hadza and Datoga samples examined, variation parameters, as well as the genotype and allele frequency distribution pattern were almost the same. At the same time, analysis of the SNP polymorphism at the A/G substitutions of the 5-HTTL locus revealed a substantial decrease of the active allele L _A frequency in the population of Hadza compared to the population of Datoga (χ² = 3.77; d.f. = 1; p = 0.052).     

酒精依赖综合征患者DRD2、DRD4和DAT基因多态性的研究

目的:探讨云南地区人群中DRD2(TaqIA、-141C)、DRD4和DAT基因多态性与酒精依赖的相关性.方法:采用聚合酶链式反应-限制性片断长度多态性(PCR-RFLP)分析技术以及聚合酶链式反应-可变数目串联重复序列多态性(PCR-VNTR)分析技术检测酒依赖组(80例)和对照组(70例)在3个候选基因中的基因型和等位基因频率.结果:上述三个基因多态性的基因型和等位基因频率在酒依赖组和对照组中差异均无统计学意义(P>0.05),对DRD2基因中的TaqIA和-141C进行单倍型分析时发现,Del/Al是一种保护单倍型,能抑制酒依赖综合征的发生.结论:在云南地区人群中,携带有Del/Al单倍型基因的人不易形成酒依赖.     

Identification of a new selective dopamine D4 receptor ligand

The dopamine D₄ receptor has been shown to play key roles in certain CNS pathologies including addiction to cigarette smoking. Thus, selective D₄ ligands may be useful in treating some of these conditions. Previous studies in our laboratory have indicated that the piperazine analog of haloperidol exhibits selective and increased affinity to the DAD₄ receptor subtype, in comparison to its piperidine analog. This led to further exploration of the piperazine moiety to identify new agents that are selective at the D₄ receptor. Compound 27 (K_iD₄ = 0.84 nM) was the most potent of the compounds tested. However, it only had moderate selectivity for the D₄ receptor. Compound 28 (K_iD₄ = 3.9 nM) while not as potent, was more discriminatory for the D₄ receptor subtype. In fact, compound 28 has little or no binding affinity to any of the other four DA receptor subtypes. In addition, of the 23 CNS receptors evaluated, only two, 5HT_1AR and 5HT_2BR, have binding affinity constants better than 100 nM (K_i <100 nM). Compound 28 is a potentially useful D₄-selective ligand for probing disease treatments involving the D₄ receptor, such as assisting smoking cessation, reversing cognitive deficits in schizophrenia and treating erectile dysfunction. Thus, further optimization, functional characterization and evaluation in animal models may be warranted.     

Activation of DRD5 (dopamine receptor D5) inhibits tumor growth by autophagic cell death

Dopamine agonists such as bromocriptine and cabergoline have been successfully used in the treatment of pituitary prolactinomas and other neuroendocrine tumors. However, their therapeutic mechanisms are not fully understood. In this study we demonstrated that DRD5 (dopamine receptor D5) agonists were potent inhibitors of pituitary tumor growth. We further found that DRD5 activation increased production of reactive oxygen species (ROS), inhibited the MTOR pathway, induced macroautophagy/autophagy, and led to autophagic cell death (ACD) in vitro and in vivo. In addition, DRD5 protein was highly expressed in the majority of human pituitary adenomas, and treatment of different human pituitary tumor cell cultures with the DRD5 agonist SKF83959 resulted in growth suppression, and the efficacy was correlated with the expression levels of DRD5 in the tumors. Furthermore, we found that DRD5 was expressed in other human cancer cells such as glioblastomas, colon cancer, and gastric cancer. DRD5 activation in these cell lines suppressed their growth, inhibited MTOR activity, and induced autophagy. Finally, in vivo SKF83959 also inhibited human gastric cancer cell growth in nude mice. Our studies revealed novel mechanisms for the tumor suppressive effects of DRD5 agonists, and suggested a potential use of DRD5 agonists as a novel therapeutic approach in the treatment of different human tumors and cancers.