Neste estudo, geramos ensaios de espectrometria de massa para detecção de 111 mutações nos genes RET, BRAF, NRAS, HRAS, KRAS, PIK3CA e AKT1 e avaliamos inúmeras linhagens celulares e tumores tiroidianos. Mostramos que as mutações dos genes BRAF e RAS refletem prognósticos distintos e que as mutações BRAF são altamente prevalentes em câncer metastático. Mutações dos genes PIK3CA e AKT1, esta última sendo reportada pela primeira vez no câncer de tiróide, são relativamente frequentes neste câncer. Avaliamos ainda a função do microRNA let-7 neste câncer. Mostramos que a ativação do rearranjo RET/PTC3 em células de tiróide PCCl3 reduz a expressão de let-7. Além disso, a transfecção deste microRNA em células TPC-1, que apresentam o rearranjo RET/PTC1, inibe a fosforilação de ERK, o crescimento celular e modula a expressão de genes do ciclo celular e diferenciação. Estes dados contribuem na aplicação de terapias dirigidas a efetores das vias PI3K e MAPK no câncer de tiróide, além de salientar o envolvimento do miRNA let-7 como um gene supressor tumoral nesta doença. / In this study, we designed an assay panel for genotyping 111 mutations by mass spectrometry in RET, BRAF, NRAS, HRAS, KRAS, PIK3CA, AKT1 and other related genes in many thyroid cancer cell lines and tumors. We show that patients with BRAF and RAS mutations have distinct prognosis and that BRAF mutations are highly prevalent in metastatic thyroid cancers. Mutations of PIK3CA and AKT1, the latter not previously described in this disease, are comparatively frequent in thyroid cancers. In addition, we evaluated the role of let-7 microRNA in this cancer. We show that RET/PTC3 activation in PCCl3 thyroid cells reduces let-7 expression. Moreover, transfection of let-7 in TPC-1 cells, which harbor RET/PTC1 rearrangement, inhibits MAPK activation, reduces cell growth and modulates the expression of cell cycle and differentiation genes. These findings may contribute to the design of therapies directed at MAPK and PI3K effectors and to highlight the function of let-7 as tumor suppressor gene in thyroid cancer.

Neste estudo, geramos ensaios de espectrometria de massa para detecção de 111 mutações nos genes RET, BRAF, NRAS, HRAS, KRAS, PIK3CA e AKT1 e avaliamos inúmeras linhagens celulares e tumores tiroidianos. Mostramos que as mutações dos genes BRAF e RAS refletem prognósticos distintos e que as mutações BRAF são altamente prevalentes em câncer metastático. Mutações dos genes PIK3CA e AKT1, esta última sendo reportada pela primeira vez no câncer de tiróide, são relativamente frequentes neste câncer. Avaliamos ainda a função do microRNA let-7 neste câncer. Mostramos que a ativação do rearranjo RET/PTC3 em células de tiróide PCCl3 reduz a expressão de let-7. Além disso, a transfecção deste microRNA em células TPC-1, que apresentam o rearranjo RET/PTC1, inibe a fosforilação de ERK, o crescimento celular e modula a expressão de genes do ciclo celular e diferenciação. Estes dados contribuem na aplicação de terapias dirigidas a efetores das vias PI3K e MAPK no câncer de tiróide, além de salientar o envolvimento do miRNA let-7 como um gene supressor tumoral nesta doença. / In this study, we designed an assay panel for genotyping 111 mutations by mass spectrometry in RET, BRAF, NRAS, HRAS, KRAS, PIK3CA, AKT1 and other related genes in many thyroid cancer cell lines and tumors. We show that patients with BRAF and RAS mutations have distinct prognosis and that BRAF mutations are highly prevalent in metastatic thyroid cancers. Mutations of PIK3CA and AKT1, the latter not previously described in this disease, are comparatively frequent in thyroid cancers. In addition, we evaluated the role of let-7 microRNA in this cancer. We show that RET/PTC3 activation in PCCl3 thyroid cells reduces let-7 expression. Moreover, transfection of let-7 in TPC-1 cells, which harbor RET/PTC1 rearrangement, inhibits MAPK activation, reduces cell growth and modulates the expression of cell cycle and differentiation genes. These findings may contribute to the design of therapies directed at MAPK and PI3K effectors and to highlight the function of let-7 as tumor suppressor gene in thyroid cancer.

Robustness is a ubiquitous property of biological systems, however, underlying mechanisms that help reinforce the optimal phenotypes despite environmental or physiological perturbations are poorly understood. C. elegans development consists of four larval stages (L1-L4) and well-characterized invariant cell lineages, within which the heterochronic pathway controls the order and timing of cell-fates. Environmental or physiological stress signals can slow or temporarily halt larval stage progression; remarkably, however, temporal cell-fate progression remains unaffected. We show that two widely conserved signaling pathways, insulin and TGF- β, that regulate C. elegans larval stage progression in response to starvation and crowding, respectively, also regulate a rewiring of the heterochronic pathway so that cell-fates remain temporally anchored to appropriate larval stages. This rewiring is mediated by the nuclear hormone receptor DAF-12, and it involves a shift from the reliance on let-7-family microRNAs to the reliance on LIN-46 for proper downregulation of the transcription factor, Hunchback-like-1 (HBL-1), which promotes L2 cell-fates and opposes L3 cell-fates. LIN-46 (which is a homolog of bacterial molybdopterin molybdenum transferase (moeA) and human gephyrin) post-translationally inhibits HBL-1 activity. LIN-46 expression is repressed by the RNA-binding protein LIN-28 at the early stages to permit HBL-1 activity and hence the proper execution of L2 cell-fates. Our results indicate that robustness mechanisms of temporal cell-fate progression in C. elegans involves 1) coordinated regulation of temporal cell-fates and larval stage progression and 2) collaboration between translational regulation exerted by microRNAs and post-translational regulation exerted by LIN-46 to coordinate HBL-1 downregulation with stage progression.

No description available.

The genes that regulate pubertal timing in the general population are not well understood. Recently, genome-wide association studies have demonstrated that genetic variants near LIN28B associate with variation in pubertal timing in humans. To investigate where within the hypothalamic-pituitary-ovarian (HPO) axis Lin28b, and its homologue Lin28a, regulate pubertal timing, expression of these genes was assessed across the pubertal transition. The finding that Lin28a/b expression decreases only in the ovary suggests that the Lin28 pathway may exert its regulatory effects with respect to puberty in the ovary. Another aim of this thesis was to examine the effect of estrogen on Lin28b expression in immortalized GnRH neuronal cells, but the data remains equivocal and detailed future studies are needed to make definitive conclusions. The ovarian expression data lay the foundation for further studies using conditional knockout mice to verify the importance of the tissue and age specific developmental pattern that was identified.

The genes that regulate pubertal timing in the general population are not well understood. Recently, genome-wide association studies have demonstrated that genetic variants near LIN28B associate with variation in pubertal timing in humans. To investigate where within the hypothalamic-pituitary-ovarian (HPO) axis Lin28b, and its homologue Lin28a, regulate pubertal timing, expression of these genes was assessed across the pubertal transition. The finding that Lin28a/b expression decreases only in the ovary suggests that the Lin28 pathway may exert its regulatory effects with respect to puberty in the ovary. Another aim of this thesis was to examine the effect of estrogen on Lin28b expression in immortalized GnRH neuronal cells, but the data remains equivocal and detailed future studies are needed to make definitive conclusions. The ovarian expression data lay the foundation for further studies using conditional knockout mice to verify the importance of the tissue and age specific developmental pattern that was identified.

Female adults of many mosquito species possess distinct physiological features adapting to blood feeding for successful reproduction. The disease pathogens that are transmitted by mosquitoes have evolved to take advantages of the indispensable blood feedings to complete their transmission cycles and to survive attacks from the mosquito's innate immune system. Normal egg development and mosquito immunity are tightly controlled by tissue- and stage-specific gene expression and coordinated by many signal molecules in the mosquito. Understanding gene regulation affecting mosquito reproduction and malaria parasites infection is of paramount importance for developing novel malaria control strategies. A growing body of evidence indicates that microRNAs (miRNAs) are involved in egg maturation and immune reactions against invading pathogens in mosquitoes. However, the molecular mechanisms by which specific miRNAs selectively modulate reproduction and the survival of pathogens are largely unknown. The miRNA-induced gene-silencing pathway in mosquitoes was mostly extrapolated from the studies of flies. To explore the dynamics of miRNAs in reproduction, I used small RNAs sequencing to monitor miRNAs expression and their association with Argonaute 1 (Ago1) and Argonaute 2 (Ago2) in the malaria mosquito Anopheles gambiae (An. gambiae) during the 72-h period immediately after blood feeding. I found the abundance and Ago loading of most of the mature miRNAs were relatively stable after blood ingestion. However, miRNAs of the miR-309/286/2944 cluster were considerably upregulated after blood feeding. I confirmed that miR-309 is essential for normal egg development by depletion of endogenous miR-309 with a specific antagomir. In addition, my results showed that the Ago association of some miRNAs was not proportional to their cellular abundance implying additional regulation at miRNA integration. To investigate the functional roles of miRNAs and define context-dependent miRNA-mRNA interactions during the reproductive process, I have applied an innovative experimental approach to study miRNA-mRNA interactome. CLEAR (covalent ligation of endogenous Argonaute-bound RNAs)-CLIP can generate miRNA-mRNA chimeras from UV-irradiation stabilized Ago-miRNA-mRNA complex. My results have defined tens of thousands of miRNA-mRNA interactions in mosquitoes, including novel targets for mosquito-specific miRNAs. Verification of the predicted interactions using mRNA-seq, ribosome-profiling, and luciferase reporter assay revealed a reliable miRNA-mRNA interaction network. Based on the detected interactions, I refined the paring rules for mosquito miRNAs and illustrated the dynamic pairing between different regions of miRNAs with their targets in vivo. The miRNA-mRNA interactions were compared using this approach at multiple time points before and after blood feeding. Importantly, this study showed that the interactions were dynamic and enriched in genes that are involved in metabolisms, supporting the proposed functions of miRNAs in coordinating the gene regulation in mosquito reproduction. Plasmodium falciparum (P. falciparum) is a major human malaria parasite. To understand the functions of miRNAs in the mosquito resistance to Plasmodium infection, we analyzed the miRNA-mRNA interactions after female mosquitoes taking a P. falciparum-infected blood meal or an uninfected blood meal. Comparison of the interactions revealed enhanced miRNA-mRNA interactions after P. falciparum infection involving a group of immunity-related genes. In summary, this study has provided a systematic view and significantly advanced our understanding of the miRNA functions in mosquito reproduction and P. falciparum infection. / PHD

MicroRNAs (miRNAs) sind eine Klasse von ca. 22 nt langen, nicht-kodierenden RNAs, welche mittels Basenpaarung die Translationsrate und Stabilität von mRNAs herabsetzen. Die vorliegende Studie untersucht mittels Hochdurchsatz-Sequenzierung Expressionsveränderungen von miRNAs nach Infektion von kultivierten Wirtszellen mit dem mikrobiellen Modellpathogen Salmonella enterica serovar Typhimurium. In Makrophagen, welche eine Schlüsselfunktion in der Orchestrierung der angeborenen Immunität spielen, wurde im Zuge der Infektion eine Induktion der miRNAs miR-21, miR-146 und miR-155 beobachtet. Darüberhinaus stellten sich alle Mitglieder der evolutionär konservierten let-7 miRNA Familie in infizierten Makrophagen als herab reguliert heraus. Es konnte gezeigt werden, dass let-7 miRNAs die zentralen Makrophagen-Zytokine IL6 und IL10 post-transkriptional reprimieren. Konsequenterweise bewirkt eine Reduktion der let-7 Expression in mikrobiell aktivierten Makrophagen eine Erhöhung der IL6 und IL10 Produktion. Weiterhin konnten den miRNAs miR-146 und miR-155 wichtige Funktionen in der Steuerung der Sensitivität und Aktivität von Makrophagen gegenüber mikrobiellen Stimuli nachgewiesen werden: während miR-146 primär die Aktivität des plasmamembranständigen Lipopolysaccharid-Rezeptors TLR4 herabsetzte und damit einer vorzeitigen inflammatorischen Makrophagenantwort vorbeugte, blieb miR-155 strikt an letztere gekoppelt, um die Aktivität diverser pro-inflammatorischer Signalwege zu begrenzen. Es konnte gezeigt werden, dass eine Stimulation des cytosolischen Immunrezeptors NOD2 eine inflammatorische Makrophagenantwort und die resultierende miR-155 Induktion begünstigt und der negativen Kontrolle durch miR-146 entzieht. Dies verhindert möglicherweise eine Hyposensitivität gegenüber zellinvasiven Pathogenen. Zusammenfassend legen diese Beobachtungen nahe, dass miRNAs zentrale Funktionen in der post-transkriptionalen Steuerung der Wirtszellantwort auf mikrobielle Pathogene ausüben. / MicroRNAs (miRNAs) are a class of approx. 22 nt long non-coding RNAs that interfere with mRNA translation and stability. Using high-throughput sequencing the present study investigated miRNA expression changes after infection of cultured host cells with the microbial model pathogen Salmonella enterica serovar Typhimurium. In macrophages, which play a key role in the orchestration of innate immunity, infection caused the induction of miRNAs miR-21, miR-146 and miR-155. Moreover, all members of the evolutionarily conserved let-7 miRNA family were down-regulated in infected macrophages. This work reports let-7 miRNAs to function in the macrophage inflammatory response by repressing the major cytokines IL6 and IL10 post-transcriptionally. Consequently a reduction of let-7 expression in microbially activated macrophages results in a specific increase in IL6 and IL10 production. Furthermore, miR-146 and miR-155 could be assigned important functions in the control of the sensitivity and activity of macrophages to microbial stimuli: while miR-146 primarily reduced the activity of the plasma membrane associated lipopolysaccharide receptor TLR4, thereby preventing a premature macrophage inflammatory response, miR-155 stayed strictly coupled to inflammation in order to limit the activity of various pro-inflammatory signaling pathways. Interestingly, it could be shown that stimulation of the cytosolic immune receptor NOD2 favors the macrophage inflammatory response and the concomitant induction of miR-155, while bypassing the negative control by miR-146. This may prevent hyposensitivity to cell-invasive pathogens. In summary, these observations suggest that miRNAs exert key functions in the post-transcriptional control of the host cell response to microbial pathogens.

La régulation de l’expression des gènes est ce qui permet à nos cellules de s’adapter à leur environnement, de combattre les infections ou, plus généralement, de produire la quantité exacte de protéine nécessaire pour répondre à un besoin spécifique. Parmi les joueurs les plus importants dans cette régulation de l’expression des gènes on retrouve les microARN (miARN). Ces petits ARN de 22 nucléotides sont présents chez la majorité des espèces multicellulaires et sont responsables du contrôle direct de plus de 30% des gènes exprimant des protéines chez les vertébrés. La famille de miARN lethal-7 (let-7) est composée de miARN parmi les plus connus et ayant des fonctions cruciales pour la cellule. La régulation du niveau des miARN let-7 est essentielle au bon développement cellulaire. La biogenèse de ces miARN, du transcrit primaire jusqu’à leur forme mature, est régulée principalement par Lin28, une protéine pluripotente très conservée. Cette protéine est composée d’un domaine cold shock (CSD) et de deux domaines de liaison au zinc. C’est grâce à ces domaines de liaison à l’ARN que Lin28 peut lier et inhiber la maturation des miARN let-7. L’objectif de cette thèse est de caractériser l’interaction entre Lin28 et le microARN précurseur let-7g afin de mieux comprendre le rôle de cette protéine dans l’inhibition de la biogenèse du miARN. À l’aide de techniques biochimiques et biophysiques, nous avons d’abord défini les principaux déterminants de l’interaction entre Lin28 et la boucle terminale du miARN précurseur let-7g (TL-let-7g). Nous avons conclu que le domaine C-terminal de Lin28, composé d’un motif riche en lysines et arginines ainsi que de deux motifs de liaison au zinc, permet à la protéine de lier spécifiquement et avec haute affinité un renflement riche en guanine conservé chez les précurseurs de la famille let-7. Aussi, parce que la séquence et la spécificité de liaison à l’ARN de ce domaine C-terminal sont semblables à celles de la protéine NCp7 du VIH, nous avons défini ce dernier comme le domaine NCp7-like de Lin28. Par la suite, nous avons caractérisé la multimérisation de trois protéines Lin28 sur la boucle terminale de pre-let-7g. Ceci a permis de réconcilier d’apparentes contradictions retrouvées dans la littérature actuelle concernant les sites de liaison de Lin28 lors de sa liaison aux miARN précurseurs. Nous avons identifié trois sites de liaison à haute affinité sur TL-let-7g qui sont liés dans un ordre précis par trois protéines Lin28. Lors de la formation du complexe multimérique, le CSD permet une déstabilisation de l’ARN, ce qui rend accessible plusieurs sites de liaison. Le domaine NCp7-like permet plutôt un assemblage ordonné de la protéine et facilite la liaison initiale de cette dernière. Ces nouveaux résultats rendent possible la mise au point d’un nouveau modèle de l’interaction entre Lin28 et le miARN précurseur let-7g. En conclusion, les études réalisées dans cette thèse apportent une meilleure compréhension des mécanismes moléculaires impliqués dans la régulation post-transcriptionnelle d’une importante famille de miARN et permettront de guider les futures études dans le domaine de recherche en pleine effervescence qu’est celui de la biogenèse des miARN. / The regulation of gene expression is what allows our cells to adapt to their environment, to fight infections or, more generally, to express the appropriate level of proteins to meet a specific need. The microRNAs (miRNAs) are among the most important players in the regulation of gene expression. These small RNAs of 22 nucleotides are present in most multicellular species and are responsible for the direct control of more than 30% of protein-expressing genes in vertebrates. The miRNA lethal-7 (let-7) family consist of some of the most studied miRNAs and plays crucial roles in the cell. The appropriate regulation of the let-7 miRNAs level is essential for proper cellular development. The biogenesis of these miRNAs, from the primary transcript to their mature form is mainly regulated by Lin28, a highly-conserved pluripotent protein. This protein is composed of a cold shock domain (CSD) and two zinc-binding domains. These RNA-binding domains allow Lin28 to bind and inhibit the maturation of the let-7 miRNA. The objective of this thesis is to characterize the interaction between the Lin28 protein and the let-7g miRNA precursor to better understand the role of this protein in the inhibition of miARN biogenesis. Using biochemical and biophysical techniques, we first identified the main determinants of the interaction between Lin28 and the terminal loop of the precursor miRNA let-7g (TL-let-7g). We concluded that the C-terminal domain of Lin28, composed of a lysine-rich and arginine-rich motif in addition to two zinc-binding motifs, is sufficient to bind with high affinity a conserved guanine-rich bulge located on the TL-let-7g. In addition, because the sequence and RNA-binding specificity of this C-terminal domain are similar to those of the HIV protein NCp7, we defined this region as the NCp7-like domain of Lin28. Subsequently, we characterized the multimerization of three Lin28 proteins on the terminal loop of pre-let-7g. This study helped to reconcile apparent contradictions found in the current literature regarding the Lin28-binding sites on miRNA precursors. We identified three high-affinity binding sites on TL-let-7g that are bound in a stepwise manner by the three Lin28 proteins. As part of the formation of the multimeric complex, both RNA-binding domains of Lin28 play an important role. The CSD destabilizes the RNA and this exposes several binding sites, whereas the NCp7-like domain allows an orderly protein assembly and facilitates the initial binding of the protein. These results lead us to propose a new model for the interaction between Lin28 and pre-let-7g. In conclusion, these studies provide a better understanding of the molecular mechanisms involved in the post-transcriptional regulation of an important family of miRNAs and will help guide future projects in the expanding research area of miRNA biogenesis.

La sclérose latérale amyotrophique (SLA) est une pathologie complexe multifactorielle dont les mécanismes de dégénérescence des motoneurones et de propagation rapide au sein du système nerveux sont encore incertains. Par l’utilisation du nématode Caenorhabditis elegans, nous avons pu investiguer génétiquement et pharmacologiquement certains facteurs entrant en jeu dans la toxicité de TDP-43 et FUS. Des mutations dominantes dans ces protéines liant l’ADN et l’ARN, structurellement et fonctionnellement proches, sont des causes de SLA familiales. Nous avons, par le passé, construit un modèle de ver transgénique possédant le gène TARDBP ou FUS codant respectivement pour les protéines humaines TDP-43 ou FUS, sous le contrôle d’un promoteur exprimé seulement dans les neurones GABAergiques. Uniquement lorsque les gènes TARDBP ou FUS sont mutés, des symptômes relatifs à la SLA apparaissent au cours du temps, à savoir une paralysie progressive et une neurodégénérescence des motoneurones GABAergiques. Nous avons voulu connaître le rôle que pouvait jouer le système immunitaire, dont des évidences croissantes montrent une implication dans la SLA, dans la protéotoxicité liée à ces protéines dans nos modèles de ver. Dans un premier temps, nous avons évalué la motricité des vers en milieu solide et en milieu liquide, et grâce à des vers transgéniques exprimant la GFP dans les neurones GABAergiques, nous avons pu quantifier la neurodégénérescence. Nos résultats soulignent un rôle prévalent de l’orthologue de la protéine du système immunitaire innée Sarm1 chez le ver, TIR-1, ainsi que les kinases en aval dans la pathologie. Nous avons pu, de surcroît, utiliser le marqueur NLP-29 dont le promoteur lié à la GFP nous indique l’activation de la voie Sarm1 dans l’ensemble du ver et non seulement dans les neurones. De manière intéressante, l’activation de ces protéines se produit entre autres dans des cellules non-neuronales de manière paracrine suggérant qu’un signal de danger opère extracellulairement et vraisemblablement à travers un récepteur membranaire. Ces dernières années, un nombre important d’études met en lumière le rôle proéminent des microARNs dans des maladies telle que la SLA. Classiquement vus comme des régulateurs de l’expression post-transcriptionnelle, ce qui en font notamment des outils antiviraux puissants, ils peuvent agir à d’autres niveaux et notamment comme ligands de récepteurs Toll-like (TLRs), eux aussi impliqués dans la SLA. iv Outre le potentiel biomarqueur de ces petites molécules, nous avons investigué leur rôle dans la neurodégénérescence observée dans la SLA. Ainsi, dans une deuxième partie d’étude, nous avons utilisé des mutants pour différentes protéines impliquées dans la biogénèse des microARNs et trouvé qu’elles étaient partie intégrante du processus de paralysie et de dégénérescence des vers TDP-43A315T. Plus encore, le microARN let-7 pourrait être une molécule signal transitant entre les neurones et les cellules avoisinantes. Enfin, des analyses bio-statistiques prédisent la possibilité que let-7 se lie au récepteur TOL-1, l’unique orthologue des TLRs chez C. elegans. Les propriétés des microARNs en font en effet des cibles de choix dans la recherche de nouveaux acteurs dans la SLA et de potentielles cibles thérapeutiques. / Amyotrophic lateral sclerosis is a complex multifactorial pathology characterized by the progressive spread of motor neuron degeneration. Unfortunalety, the underlying disease mechanisms remain unclear. By using the nematode Caenorhabditis elegans, we were able to investigate genetically and pharmacologically some factors involved in TDP-43 or FUS proteotoxicity. Dominant mutations in these structurally and functionally similar DNA/RNA binding proteins, are causative for familial ALS. We have constructed transgenic C. elegans models expressing human TARDBP or FUS genes - encoding respectively TDP-43 and FUS - only in GABAergic motor neurons. In these transgenics animals, the expression of mutant TARDBP or FUS alleles results in early the motor deficits leading to age-dependent paralysis accompanied by neuronal protein aggregation. Using transgenic strain expressing GFP in GABAeric neurons, we found an increased rate of neurodegeneration in TDP-43 and FUS mutants. With these models we investigated the potential role of the innate immune system as a modifier of these phenotypes. Our results highlight a prevalent role for the worm’s innate immune system, and specifically the TIR-1/Sarm1 pathway and associated downstream kinases in neurodegeneration. We used GFP fluorescence linked to NLP-29 promoter to indicate Sarm1 pathway activation in the entire worm. Interestingly, activation of the TIR-1/Sarm1 pathway occurs in a paracrine manner in non-neuronal cells, suggesting that a danger signal operates extracellularly likely through a membrane receptor. In a past few years, a number of studies have highlighted the prominent role of microRNAs in diseases such as ALS. Traditionally seen as post-transcriptional regulators, what makes them powerful antiviral tools is that they can act at other levels and in particular as Toll-like receptors (TLRs) ligands, also involved in ALS. In addition to the biomarker potential of these small molecules, we investigated their role in the neurodegeneration observed in ALS. As a result, in the a second section of this study, we used worms mutant for several proteins involved in the biogenesis of microRNAs and found that they were involved in the process of TDP-43A315T-independent paralysis and neurodegeneration. Moreover, the microRNA let-7 seems to be a signal molecule involved in the non-cell autonomous trans-neuronal and trans-cellular spread of motor neuron degeneration. Finally, bio-statistical analyzes predict the possibility that let-7 binds to the vi TOL-1 receptor, the single ortholog of TLRs in C. elegans. Thus microRNAs may be prime targets for ALS therapeutic intervention.