Genetic variants and abnormal processing of pre-miR-182, a circadian clock modulator, in major depression patients with late insomnia.

Previous studies in mice have reported five different microRNAs (miRNAs; miR-219-1/132/183/96/182) to be modulators of the endogenous circadian clock and have presented experimental evidence for some of the genes involved in the molecular clock machinery as target sites. Moreover, disruption of circadian rhythms has long been implicated in the pathophysiology of major depression (MD). We investigated these miRNAs and some of their target sites at the sequence and functional levels as possible predisposing factors for susceptibility to MD and related chronobiological subphenotypes. Mutational screening was performed in a sample of 359 MD patients and 341 control individuals. We found a significant association between the T allele of the rs76481776 polymorphism in the pre-miR-182 and late insomnia in MD patients. Previous studies have reported an association between insomnia and CLOCK gene, a predicted miR-182 target site. A significant overexpression of miR-182 was detected by quantitative real-time polymerase chain reaction in cells transfected with the mutated form of the pre-miR-182 when compared with wild-type form. Moreover, a significant reduction in luciferase activity of plasmids with 3' UTR of ADCY6, CLOCK and DSIP genes was shown when transfecting cells with the mutated form of pre-miR-182 compared with cells that did not express miR-182. These data indicate that abnormal processing of pre-miR-182 in patients carrying the T allele of the rs76481776 polymorphism may contribute to the dysregulation of circadian rhythms in MD patients with insomnia, which could influence expression levels of the mature form of miR-182 and might increase downregulation in some of its target genes.

Positive selection and gene conversion drive the evolution of a brain-expressed snoRNAs cluster.

HBII-52 small nucleolar RNAs (snoRNAs) are brain-expressed posttranscriptional modifiers of serotonin receptor 2C RNA. They are organized in a cluster of 47 highly homologous gene copies spanning 100 kb at chromosome 15q11.2. Nucleotide diversity at HBII-52 snoRNA gene cluster in African and European descent populations was analyzed via resequencing of 25 functional snoRNA gene copies. Ninety-four variants were detected, from which 74 are novel. Only 16 variants are shared between Africans and Europeans. We also report a novel Yoruba-specific copy-number variant representing a 5.2-kb polymorphic deletion and resulting in a chimerical functional snoRNA copy. In both populations, the snoRNA genes are characterized by high density of single nucleotide polymorphisms and an excess of low-frequency variants. However, the variability patterns are strictly population specific and there is an extreme divergence in allele frequencies in both resequencing and HapMap data. Several tests of neutrality strongly suggest that the observed extreme population divergence at the HBII-52 region results from positive selection in Europeans. Our analysis of HBII-52 nucleotide variability spectrum shows that gene conversion is the main factor introducing variability at the cluster. Sixty-five substitutions (69%) correspond to a paralogous sequence variant (PSV) in another copy and occur at potential gene conversion tracts of >5 bp. We detected several interparalogue gene-conversion events that involve more than one PSV, with individual frequency patterns suggestive of recurrent gene conversion. Analysis based on derived and ancestral allele distribution shows that gene conversion is at least twice more frequent than point mutations. Gene conversion is an important factor in disrupting patterns of linkage disequilibrium (LD) at short scales. Consistent with this, we detect punctual breaks of LD at gene conversion sites while the overall LD at the HBII-52 cluster is high in both study populations.