The telomeric repeat containing RNA TERRA represents a class of long non-coding RNAs transcribed from telomeres. TERRA has been shown to play key roles in telomere maintenance. During past years it has been reported that TERRA interacts with telomerase, suggesting it may act as regulator of telomerase. However, the role of TERRA in telomerase activity in human cells is still unknown and it needs to be further investigated. Herein, we investigate the role of TERRA in telomerase activity in human cancer cells by exploiting different experimental conditions. By using single molecule RNA FISH (smiFISH) combined with confocal microscopy, we demonstrated that TERRA and the telomerase RNA subunit hTR colocalize in cancer cells. We observed that these events mainly occur in the nucleoplasm, while a fraction of TERRA transcripts colocalize with hTR molecules also at telomeres. This result suggested us the possibility of a localization-dependent role of TERRA in the regulation of telomerase activity. Surprisingly, by studying TERRA and hTR interactions during telomere length homeostasis, we observed that fewer TERRA molecules localize at chromosome ends when telomeres are elongated by telomerase. Furthermore, the fraction of telomeric TERRA-hTR colocalizing foci markedly decreased during telomere elongation. We observed that telomere shortening correlated with increased TERRA levels, in line with previously reported findings. Intriguingly, by quantifying the integrated density of the telomeric foci in smiFISH experiments combined with immunofluorescence (IF), we observed that TERRA transcripts preferentially localize to telomeres showing a brighter signal intensity as compared to the average telomeric signal of the cell, suggesting a preferential recruitment of TERRA to longer chromosome ends. These results suggest that TERRA transcripts may localize to telomeres in trans and that a displacement of TERRA from chromosome ends may be required for telomere elongation by telomerase. To gain insight into the role of TERRA in the regulation of telomerase, we used antisense oligonucleotides to deplete TERRA in cells. Interestingly, TERRA depletion resulted in increased telomerase localization to telomeres. Altogether, our findings support a model in which telomeric TERRA transcripts act as negative regulators of telomerase activity at telomeres.

Le travail décrit dans cette thèse porte sur une nouvelle méthodologie de caractérisation des circuits sécurisés basée sur une rétro-conception matérielle partielle : d’une part afin d’améliorer l’injection de fautes laser, d’autre part afin de détecter la présence de Chevaux de Troie Matériels (CTMs). Notre approche est dite partielle car elle est basée sur une seule couche matérielle du composant et car elle ne vise pas à recréer une description schématique ou fonctionnelle de l’ensemble du circuit.Une méthodologie invasive de rétro-conception partielle bas coût, rapide et efficace est proposée. Elle permet d’obtenir une image globale du circuit où seule l’implémentation des caissons des transistors est visible. La mise en œuvre de cette méthodologie est appliquée sur différents circuits sécurisés. L’image obtenue selon la méthodologie déclinée précédemment est traitée afin de localiser spatialement les portes sensibles, voire critiques en matière de sécurité. Une fois ces portes sensibles identifiées, nous caractérisons l’effet du laser sur différentes parties de ces cellules de bases et nous montrons qu’il est possible de contrôler à l’aide d’injections de fautes laser la valeur contenue dans ces portes. Cette technique est inédite car elle valide le modèle de fautes sur une porte complexe en technologie 90 nm. Pour finir une méthode de détection de CTMs est proposée avec le traitement de l’image issue de la rétro-conception partielle. Nous mettons en évidence l’ajout de portes non répertoriées avec l’application sur un couple de circuits. La méthode permet donc de détecter, à moindre coût, de manière rapide et efficace la présence de CTMs. / The work described in this thesis covers an integrated circuit characterization methodology based on a partial hardware reverse engineering. On one hand in order to improve integrated circuit security characterization, on the other hand in order to detect the presence of Hardware Trojans. Our approach is said partial as it is only based on a single hardware layer of the component and also because it does not aim to recreate a schematic or functional description of the whole circuit. A low cost, fast and efficient reverse engineering methodology is proposed. The latter enables to get a global image of the circuit where only transistor's active regions are visible. It thus allows localizing every standard cell. The implementation of this methodology is applied over different secure devices. The obtained image according to the methodology declined earlier is processed in order to spatially localize sensible standard cells, nay critical in terms of security. Once these cells identified, we characterize the laser effect over different location of these standard cells and we show the possibility with the help of laser fault injection the value they contain. The technique is novel as it validates the fault model over a complex gate in 90nm technology node.Finally, a Hardware Trojan detection method is proposed using the partial reverse engineering output. We highlight the addition of few non listed cells with the application on a couple of circuits. The method implementation therefore permits to detect, without full reverse-engineering (and so cheaply), quickly and efficiently the presence of Hardware Trojans.