Post-genomic era and gene discovery for psychiatric diseases: there is a new art of the trade? The example of the HUMTH01 microsatellite in the Tyrosine Hydroxylase gene

The association of genetic polymorphisms within the dopaminergic system with nicotine dependence: A narrative review

Nicotine, the main compound in cigarettes, leads to smoking addiction. Nicotine acts on the limbic dopamine reward loop in the midbrain by binding to nicotinic acetylcholine receptors, promoting the release of dopamine, and resulting in a rewarding effect or satisfaction. This satisfaction is essential for continued and compulsive tobacco use, and therefore dopamine plays a crucial role in nicotine dependence. Numerous studies have identified genetic polymorphisms of dopaminergic pathways which may influence susceptibility to nicotine addiction. Dopamine levels are greatly influenced by synthesis, storage, release, degradation, and reuptake-related genes, including genes encoding tyrosine hydroxylase, dopamine decarboxylase, dopamine transporter, dopamine receptor, dopamine 3-hydroxylase, catechol-O-methyltransferase, and monoamine oxidase. In this paper, we review research progress on the effects of polymorphisms in the above genes on downstream smoking behavior and nicotine dependence, to offer a theoretical basis for the elucidation of the genetic mechanism underlying nicotine dependence and future personalized treatment for smoking cessation.

Transgenic mice expressing yellow fluorescent protein under control of the human tyrosine hydroxylase promoter

Pathogenesis of Parkinson's disease and related catecholaminergic neurological disorders is closely associated with changes in the levels of tyrosine hydroxylase (TH). Therefore, investigation of the regulation of the TH gene system should assist in understanding the pathomechanisms involved in these neurological disorders. To identify regulatory domains that direct human TH expression in the central nervous system (CNS), we generated two transgenic mouse lines in which enhanced yellow fluorescent protein (EYFP) is expressed under the control of either 3.2-kb (hTHP-EYFP construct) human TH promoter or 3.2-kb promoter with 2-kb 3'-flanking regions (hTHP-ex3-EYFP construct) of the TH gene. In the adult transgenic mouse brain, the hTHP-EYFP construct directs neuron-specific EYFP expression in various CNS areas, such as olfactory bulb, striatum, interpeduncular nucleus, cerebral cortex, hippocampus, and particularly dentate gyrus. Although these EYFP-positive cells were identified as mature neurons, few EYFP-positive cells were TH-positive neurons. On the other hand, we could detect the EYFP mRNA expression in a subset of neurons in the olfactory bulb, midbrain, and cerebellum, in which expression of endogenous TH is enriched, with hTHP-ex3-EYFP transgenic mice. These results indicate that the 3.2-kb sequence upstream of the TH gene is not sufficient for proper expression and that the 2-kb sequence from the translation start site to exon 3 is necessary for expression of EYFP in a subset of catecholaminergic neurons.

Extracellular guanosine and GTP promote expression of differentiation markers and induce S-phase cell-cycle arrest in human SH-SY5Y neuroblastoma cells

SH-SY5Y neuroblastoma cells, a model for studying neuronal differentiation, are able to differentiate into either cholinergic or dopaminergic/adrenergic phenotypes depending on media conditions. Using this system, we asked whether guanosine (Guo) or guanosine-5'-triphosphate (GTP) are able to drive differentiation towards one particular phenotype. Differentiation was determined by evaluating the frequency of cells bearing neurites and assessing neurite length after exposure to different concentrations of Guo or GTP for different durations. After 6 days, 0.3 mM Guo or GTP induced a significant increase in the number of cells bearing neurites and increased neurite length. Western blot analyses confirmed that purines induced differentiation; cells exposed to purines showed increases in the levels of GAP43, MAP2, and tyrosine hydroxylase. Proliferation assays and cytofluorimetric analyses indicated a significant anti-proliferative effect of purines, and a concentration-dependent accumulation of cells in S-phase, starting after 24 h of purine exposure and extending for up to 6 days. A transcriptional profile analysis using gene arrays showed that an up-regulation of cyclin E2/cdk2 evident after 24 h was responsible for S-phase entry, and a concurrent down-regulation of cell-cycle progression-promoting cyclin B1/B2 prevented S-phase exit. In addition, patch-clamp recordings revealed that 0.3 mM Guo or GTP, after 6 day incubation, significantly decreased Na(+) currents. In conclusion, we showed Guo- and GTP-induced cell-cycle arrest in neuroblastoma cells and suggest that this makes these cells more responsive to differentiation processes that favor the dopaminergic/adrenergic phenotype.

Sex and Age Specificity of Susceptibility Genes Modulating Survival at Old Age

OBJECTIVE

We aimed to investigate the influence of the genetic variability of candidate genes on survival at old age in good health.

METHODS

First, on the basis of a synthetic survival curve constructed using historic mortality data taken from the Italian population from 1890 onward, we defined three age classes ranging from 18 to 106 years. Second, we assembled a multinomial logistic regression model to evaluate the effect of dichotomous variables (genotypes) on the probability to be assigned to a specific category (age class). Third, we applied the regression model to a cross-sectional dataset (10 genes; 972 subjects selected for healthy status) categorized according to age and sex.

RESULTS

We found that genetic factors influence survival at advanced age in good health in a sex- and age-specific way. Furthermore, we found that genetic variability plays a stronger role in males than in females and that, in both genders, its impact is especially important at very old ages.

CONCLUSIONS

The analyses presented here underline the age-specific effect of the gene network in modulating survival at advanced age in good health.

Will genetic polymorphism of tetranucleotide sequences help in the diagnostics of major psychiatric disorders?

Expecting a significant breakthrough in the diagnosis of complex disorders of neuropsychiatric background, intensive efforts are taking place to establish genetic markers correlated with these disorders. During the last decade, this research was focused on code regions connected with neurotransmission and metabolism of catecholamines. Nowadays big diagnostic expectations are associated with sequences of STR type, which are widespread throughout the genome. These microsatellite sequences do not code proteins, but may have function of regulatory elements in the process of gene transcription and expression. One of these is polymorphic TH01 locus with TCAT tetranucleotide repetitive motive. It is located in chromosomal position 11p15 in the first intron of the tyrosine hydroxylase gene (TH). We examined the existence of the association between polymorphism of TH01 marker and schizophrenia. The results of statistical comparative analysis between neuropsychiatric patients from Poland and their regionally matched healthy subjects were presented.

Meta-analysis shows association between the tryptophan hydroxylase (TPH) gene and schizophrenia

A number of studies have suggested an association between schizophrenia and the tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH) genes. On the other hand, several studies attempting to replicate these findings have produced mixed results, possibly reflecting inadequate statistical power of the individual studies as well as the heterogeneity inherent in schizophrenia. In an attempt to clarify this inconsistency our meta-analysis has combined all the studies using multiple research methods published up to February 2006 to give a comprehensive picture of the role of three hydroxylase-related genes. The TPH A218C/A779C (OR = 1.18, 95% C.I. 1.06-1.33, P = 0.004) revealed a significant association with schizophrenia. However, the evidence for the TH and phenylalanine hydroxylase (PAH) genes was weak. No publication bias was detected in current studies. The findings, which may implicate the involvement of TPH in the pathogenesis of schizophrenia, have potentially important clinical, scientific and public health implications as well as providing a putative basis for the study of hydroxylase-related drugs. To our knowledge, this is the first meta-analysis of association between the three genes and schizophrenia.

Nicotine dependence in a prospective population-based study of adolescents

Dopamine is a key neurotransmitter of the mesolimbic reward pathway in the human brain, and tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine biosynthesis. Consequently, the gene encoding TH is a strong candidate for involvement in the genetic component of addiction. The importance of this gene in nicotine dependence is supported by many studies showing a link between nicotine administration and TH expression. A functional tetranucleotide repeat polymorphism within intron 1 of the TH gene (HUMTH01-VNTR) has been shown to modify tobacco use in two independent Caucasian samples from the USA and Australia. Using information drawn from an eight-wave Australian population-based longitudinal study of adolescent health, we tested the effect of the HUMTH01-VNTR on nicotine dependence. Comparisons were made between dependent smokers and non-dependent smokers. These data provide further support for a protective association between the K4 allele and dependent smoking (odds ratio 0.54, 95% confidence interval 0.28-1.0). No associations were observed at any of three other common TH polymorphisms (rs6356, rs6357 and HUMTH01-PstI). Including these data, three independent studies, two of which use identical phenotypes, have now identified a protective relationship between the K4 allele of the functional HUMTH01-VNTR polymorphism and high-level smoking.

Establishment of transgenic mice carrying gene encoding human zinc finger protein 191

AIM: Human zinc finger protein 191 (ZNF191) was cloned and characterized as a Krüppel-like transcription factor, which might be relevant to many diseases such as liver cancer, neuropsychiatric and cardiovascular diseases. Although progress has been made recently, the biological function of ZNF191 remains largely unidentified. The aim of this study was to establish a ZNF 191 transgenic mouse model, which would promote the functional study of ZNF191.

METHODS: Transgene fragments were microinjected into fertilized eggs of mice. The manipulated embryos were transferred into the oviducts of pseudo-pregnant female mice. The offsprings were identified by PCR and Southern blot analysis. ZNF 191 gene expression was analyzed by RT-PCR. Transgenic founder mice were used to establish transgenic mouse lineages. The first generation (F1) and the second generation (F2) mice were identified by PCR analysis. Ten-week transgenic mice were used for pathological examination.

RESULTS: Four mice were identified as carrying copies of ZNF191 gene. The results of RT-PCR showed that ZNF 191 gene was expressed in the liver, testis and brain in one of the transgenic mouse lineages. Genetic analysis of transgenic mice demonstrated that ZNF 191 gene was integrated into the chromosome at a single site and could be transmitted stably. Pathological analysis showed that the expression of ZNF 191 did not cause obvious pathological changes in multiple tissues of transgenic mice.

CONCLUSION: ZNF 191 transgenic mouse model would facilitate the investigation of biological functions of ZNF191 in vivo.

Allelic variations in gene expression

PURPOSE OF REVIEW

Genetic variants determine phenotypic variability. Many genetic studies suggest that protein structural variations predispose the population to more than 1000 different hereditary diseases. Unfortunately, despite the study of genetic polymorphisms for many decades, the milder phenotypic variations believed to account for most human physical and behavioral differences and underlying the most common human genetic diseases (including cancers) cannot be accounted for easily by these variations in the protein coding sequences. Thus, it has been hypothesized that the study of natural differential expression presenting within and among populations may enhance understanding of human phenotypic variation.

RECENT FINDINGS

During the last year, reports identifying variations in gene expression in different organisms and finding subtle changes of gene expression associated with common genetic disease have pointed to variations in gene expression as playing a central role in molecular evolution and human disease. Advances in the functional analysis of gene regulatory networks-in particular, new methods for distinguishing cis-acting components from trans-acting factors-have provided the impetus for these discoveries.

SUMMARY

This review represents current knowledge about allelic variation in gene expression and its increasingly important role in understanding the genotype-phenotype relation. Characterization of these allelic variations may open largely uncharted territory in genomics for biomedical researchers and may eventually lead to the discovery of the causative genes of common hereditary diseases and their mechanism of action.