Nuclear Outsourcing of RNA Interference Components to Human Mitochondria

MicroRNAs (miRNAs) are small non-coding RNAs that associate with Argonaute proteins to regulate gene expression at the post-transcriptional level in the cytoplasm. However, recent studies have reported that some miRNAs localize to and function in other cellular compartments. Mitochondria harbour their own genetic system that may be a potential site for miRNA mediated post-transcriptional regulation. We aimed at investigating whether nuclear-encoded miRNAs can localize to and function in human mitochondria. To enable identification of mitochondrial-enriched miRNAs, we profiled the mitochondrial and cytosolic RNA fractions from the same HeLa cells by miRNA microarray analysis. Mitochondria were purified using a combination of cell fractionation and immunoisolation, and assessed for the lack of protein and RNA contaminants. We found 57 miRNAs differentially expressed in HeLa mitochondria and cytosol. Of these 57, a signature of 13 nuclear-encoded miRNAs was reproducibly enriched in mitochondrial RNA and validated by RT-PCR for hsa-miR-494, hsa-miR-1275 and hsa-miR-1974. The significance of their mitochondrial localization was investigated by characterizing their genomic context, cross-species conservation and instrinsic features such as their size and thermodynamic parameters. Interestingly, the specificities of mitochondrial versus cytosolic miRNAs were underlined by significantly different structural and thermodynamic parameters. Computational targeting analysis of most mitochondrial miRNAs revealed not only nuclear but also mitochondrial-encoded targets. The functional relevance of miRNAs in mitochondria was supported by the finding of Argonaute 2 localization to mitochondria revealed by immunoblotting and confocal microscopy, and further validated by the co-immunoprecipitation of the mitochondrial transcript COX3. This study provides the first comprehensive view of the localization of RNA interference components to the mitochondria. Our data outline the molecular bases for a novel layer of crosstalk between nucleus and mitochondria through a specific subset of human miRNAs that we termed ‘mitomiRs’

Homozygous frameshift mutations in FAT1 cause a syndrome characterized by colobomatous-microphthalmia, ptosis, nephropathy and syndactyly

A failure in optic fissure fusion during development can lead to blinding malformations of the eye. Here, we report a syndrome characterized by facial dysmorphism, colobomatous microphthalmia, ptosis and syndactyly with or without nephropathy, associated with homozygous frameshift mutations in FAT1. We show that Fat1 knockout mice and zebrafish embryos homozygous for truncating fat1a mutations exhibit completely penetrant coloboma, recapitulating the most consistent developmental defect observed in affected individuals. In human retinal pigment epithelium (RPE) cells, the primary site for the fusion of optic fissure margins, FAT1 is localized at earliest cell-cell junctions, consistent with a role in facilitating optic fissure fusion during vertebrate eye development. Our findings establish FAT1 as a gene with pleiotropic effects in human, in that frameshift mutations cause a severe multi-system disorder whereas recessive missense mutations had been previously associated with isolated glomerulotubular nephropathy

Elimination of arsenic traces contained in liquid effluents by chromatographic treatment

Our present work is included in a development plan of a two-step detoxication process of arsenical by-products originated from chemical warfare destruction effluents [1]. The first method studied was classical anion exchange chromatography. Less than 1% of the anion exchanger capacity is used to fix arsenate ions for a Cl$^-$/AsO$_4^{3-}$ concentration ratio equal to 100. Because of the lack of anion exchanger selectivity, the use of more selective adsorbents has been investigated, namely a macroporous cation exchange resin (BioRad AGMP-50 resin). We confirm that the As$^{\rm III}$ and As$^{\rm V}$ retention does not depend on the nature of the resin functional groups and that only the ferric hydroxide precipitate is involved in the retention. We also show that the arsenic available exchanger capacity is not significantly affected by high concentrations in chloride ions (1 mol L$^{-1}$), and it seems that the kinetics of arsenite and arsenate ions fixation is better in presence of chlorides. The use of the exchanger for the complete detoxication of arsenic trace (10 ppm) solutions in presence of high contents in chlorides (1 to 3 mol L$^{-1}$) leads to an effluent volume equal to 280 and 540 times the resin bed volume, for AsIII and AsV respectively. The effluent thereby obtained has an arsenic concentration lower than the M.C.L. (100 ppb)

Hak Azasi Manusia Dalam Islam

xiv + 273 hal.: 20 Cmn