Psychiatric genetics: Analysis of complex genetic traits {PSYGEN} (R. Meloni, N. Faucon-Biguet, J. Mallet)
The PSYGEN group, at the “Laboratoire de Génétique de la Neurotransmission (LGN)”, has developed a genomic project based on the whole genome scan analysis and the candidate gene association/functional studies approaches in order to identify and validate as therapeutic targets the genes of predisposition to bipolar disorder (BD) and schizophrenia (SZ). These functional genetic studies will help to formulate new hypotheses on the etiology of psychiatric diseases. In the frame work of this project, several hundreds of affected sib pair and trio nuclear families, casecontrol and extended pedigree samples (Fig 1) have been collected in genetically isolated populations by an international clinical network coordinated by the PSYGEN group in collaboration with SanofiAventis (SA), a pharmacological company. Several loci linked to BD or SZ have been discovered following the analysis of a high throughput whole genome scan performed on the sib-pair families by the SA genomics center. These results have been validated by fine mapping and a linkage disequilibrium study is underway for identifying the risk genes implicated in the etiology of these diseases. Association studies using the polymorphic HUMTH01 microsatellite have shown the involvement of the Tyrosine Hydroxylase gene (TH), a major candidate for neuropsychiatric diseases, in the genetic predisposition both to BD and SZ. Functional and epigenetic studies have established that the risk associated polymorphic tetrarepeat sequence of the HUMTH01 microsatellite in the TH gene has quantitative effect on gene expression (Fig 2). Moreover, specific transcription factors have been isolated that bind this sequence with different affinities related to the number of repetitions. Thus, these results reveal a novel molecular mechanism for the expression of quantitative genetic traits. Finally, the ongoing in vivo characterization by RNAi, DNA microarray and Chromatin Immune Precipitation studies of the genes targeted by the tetrarepeat-associated
transcription factors has allowed the identification of several patterns in genetic networks that may be implicated in the etiology of neuropsychiatric diseases. This project is also benefiting from recent breakthroughs at the LGN concerning, for example, the engineering of inducible integrative siRNA vectors or the discovery maternal genetic make-up effects on the fetal brain. The inducible siRNA technique will allow for rapid generation of new animal models by the spatio-temporal mastering of the knock-down of the gene(s) of interest. The evaluation of epigenetic factors such as imprinting, DNA methylation and maternal effects will allow for widening the scope of the genetic studies by taking into account the environmental component that plays a major role in psychiatric diseases. The extension of the functional studies with these integrated approaches to the new candidate genes issued from the genomic linkage disequilibrium studies and their networking partners will result in the validation of an increasing number of targets and biomarkers for the diagnosis, prognosis and therapy of BD and SZ. Also, these studies will allow for generating new hypotheses on the etiology of psychiatric diseases. Selected Publications
Albanese V, Biguet NF, Kiefer H, Bayard E., Mallet J, Meloni R. Quantitative effects on gene silencing by allelic variation at a tetranucleotide microsatellite. Hum Mol Genet. 10:1785-1792, 2001. Arányi T, Kerjean A, Toth S, Mallet J, Meloni R, Paldi A. Paradoxical methylation of the tyrosine hydroxylase gene in mouse preimplantation embryos. Genomics. 80: 558-563, 2002. Arányi T, Faucheux BA, Khalfallah O, Vodjdani G, Faucon Biguet N, Mallet J,, Meloni, R. The tissue-specific methylation of the human tyrosine hydroxylase gene reveals new regulatory elements in the first exon. J Neurochem. 94: 129-139, 2005.
Tejedor-Real P, Vogel R, Mallet J, Faucon Biguet N. Gi/Go protein-dependent presynaptic mechanisms are involved in clozapine-induced down-regulation of tyrosine hydroxylase in PC12 cells. J Neurosci Res. 81: 739-745, 2005. Amar L, Desclaux M, Faucon-Biguet N, Mallet J, Vogel R. Control of small inhibitory RNA levels and RNA interference by
doxycycline induced activation of a minimal RNA polymerase III promoter. Nucleic Acids Res. 34(5): e37, 2006. Tejedor-Real P, Sahagun M, Biguet NF, Mallet J. Neonatal handling prevents the effects of phencyclidine in an animal model of negative symptoms of schizophrenia. Biol Psychiatry. 61: 865-872, 2007.
Fig 1: Bipolar disorder extended pedigree. All the patients (in red) from an isolated village in Sardinia were recruited by the Institute of Clinical Pharmacology (Director: Pr. Maria Del Zompo), University of Cagliari, Italy. The reconstruction of the genealogical tree through 13 generation using City Hall and Parish data shows that all the affected persons in the village descend from a founder couple living at the beginning of the XVIIth century (Census of 1605).
Fig 2: Microsatellite HUMTH01 and quantitative effects on gene transcription. The sequence encompassing the human Tyrosine Hydroxylase gene from the proximal promoter to the third exon was fused in frame with the luciferase reporter gene. The progressive increase of the number of TCAT repeats in their orthologous position in the first intron of the TH gene resulted in the quantitative inhibition of gene transcription as evaluated by luciferase activity measurement.