Simultaneous analysis of serotonin transporter, tryptophan hydroxylase 1 and 2 gene expression in the ventral prefrontal cortex of suicide victims.

Serotonergic signaling abnormalities have been implicated in suicide. Tryptophan hydroxylase (TPH), the rate limiting enzyme of serotonin biosynthesis and the serotonin transporter (SLC6A4), involved in the reuptake of serotonin from the synaptic gap, play major role in serotonergic signaling. In this study, we aimed to compare the levels of expression of these serotonin-related genes between suicide completers and controls and to identify genetic loci involved in their regulation. SLC6A4, TPH1, and TPH2 mRNA levels were measured in the ventral prefrontal cortex (VPFC) of 39 suicide completers and 40 matched controls. To identify the molecular basis of gene expression variation, we performed association studies between cis-acting polymorphisms and SLC6A4, TPH1, and TPH2 transcript levels. Finally, association analyses were carried out between suicide and TPH2 cis-single nucleotide polymorphisms (SNPs) in cohorts of 154 suicide completers and 289 control subjects. Whereas SLC6A4 and TPH1 mRNA expression levels did not differ between suicides and controls, TPH2 levels were found significantly increased (P = 0.003) in suicide completers. We observed that SNP rs10748185 located in the promoter region of TPH2 significantly affect levels of TPH2 mRNA expression. However, we did not find positive association between this eQTL (rs10748185) and suicide. Here, we report the simultaneous analysis of the expression of three serotonin-related genes in the VPFC of suicide victims and controls. This study showed that TPH2 expression levels were increased in the VPFC of suicide victims. Although, we identified a genetic variant that explains variance in TPH2 expression, we did not find evidence associating this cis-regulatory SNP with suicidal behavior.

Genetic and epigenetic analysis of SSAT gene dysregulation in suicidal behavior.

It has recently been proposed that the SSAT gene plays a role in the predisposition to suicidal behavior. SSAT expression was found to be down-regulated in the brain of suicide completers. In addition, a single nucleotide polymorphism (SNP) rs6526342 was associated both with variation in SSAT expression and with suicidal behavior. In this study, we aimed to characterize the relationship between SSAT dysregulation and suicide behavior. To this end, we measured SSAT expression levels in the ventral prefrontal cortex (VPFC) of suicide completers (n = 20) and controls (n = 20) and found them to be significantly down-regulated in suicide victims (P = 0.007). To identify the basis of the regulation of SSAT expression, we performed an association analysis of 309 SNPs with SSAT transcript levels in 53 lymphoblastoid cell lines from the CEPH collection. We then examined the methylation status of the SSAT promoter region in males and females suicide completers and control subjects whose SSAT brain expression had been measured. We found no evidence to support a role for SNPs in controlling the level of SSAT expression. SSAT promoter methylation levels were not different between suicide completers and controls and did not correlate with SSAT expression levels. In addition, we found no indication of a genetic association between suicidal behavior and SNPs located within the SSAT gene. Our study provides new results which show that dysregulation of SSAT expression does play a role in suicide behavior. However, our data do not support any association between rs6526342 and variation in SSAT expression or suicidal behavior.

Evolutionary forces shape the human RFPL1,2,3 genes toward a role in neocortex development.

The size and organization of the brain neocortex has dramatically changed during primate evolution. This is probably due to the emergence of novel genes after duplication events, evolutionary changes in gene expression, and/or acceleration in protein evolution. Here, we describe a human Ret finger protein-like (hRFPL)1,2,3 gene cluster on chromosome 22, which is transactivated by the corticogenic transcription factor Pax6. High hRFPL1,2,3 transcript levels were detected at the onset of neurogenesis in differentiating human embryonic stem cells and in the developing human neocortex, whereas the unique murine RFPL gene is expressed in liver but not in neural tissue. Study of the evolutionary history of the RFPL gene family revealed that the RFPL1,2,3 gene ancestor emerged after the Euarchonta-Glires split. Subsequent duplication events led to the presence of multiple RFPL1,2,3 genes in Catarrhini ( approximately 34 mya) resulting in an increase in gene copy number in the hominoid lineage. In Catarrhini, RFPL1,2,3 expression profile diverged toward the neocortex and cerebellum over the liver. Importantly, humans showed a striking increase in cortical RFPL1,2,3 expression in comparison to their cerebellum, and to chimpanzee and macaque neocortex. Acceleration in RFPL-protein evolution was also observed with signs of positive selection in the RFPL1,2,3 cluster and two neofunctionalization events (acquisition of a specific RFPL-Defining Motif in all RFPLs and of a N-terminal 29 amino-acid sequence in catarrhinian RFPL1,2,3). Thus, we propose that the recent emergence and multiplication of the RFPL1,2,3 genes contribute to changes in primate neocortex size and/or organization.

Pax6-induced alteration of cell fate: shape changes, expression of neuronal alpha tubulin, postmitotic phenotype, and cell migration.

The transcription factor Pax6 plays an important role in the development of the central nervous system. To understand its mechanism of action, we transduced HeLa cells with a Pax6-expressing lentiviral vector. Upon transduction, HeLa cells markedly changed shape and formed neuritelike extensions. Pax6-transduced HeLa cells expressed high levels of neuronal alpha3 tubulin, demonstrating a partial transdifferentiation towards a neuronal phenotype. Neurons are postmitotic cells. Pax6-transduced HeLa cells became postmitotic through mechanisms involving up-regulation of p53 and cyclin-dependent kinase inhibitor p21. One of the most striking effects of Pax6 was observed by time-lapse videomicroscopy: cells started to dissociate from cell clusters and displayed intense migratory activity. Migration was accompanied by dynamic and reversible shape changes. Our results identified three elements of Pax6 action: (i) expression of neuron-specific genes; (ii) establishment of a postmitotic phenotype; and (iii) involvement in the regulation of cell shape and cell migration.