Les protéines signal Hedgehog (HH) sont des acteurs majeurs du développement animal et de la carcinogenèse. Leur transduction requiert la protéine à 7 domaines transmembranaires Smoothened (SMO) dont l’activité est régulée par Patched (PTC), un récepteur et antagoniste d’HH. PTC et HH régulent le trafic, la phosphorylation et l’accumulation de SMO mais de nombreux aspects de sa régulation restent incompris. Au cours de ma thèse, j’ai travaillé sur Smaug, un nouveau partenaire de SMO chez la drosophile identifié au laboratoire dans un crible double-hybride. Smaug est connue pour lier et réprimer de nombreux ARNm au cours de l’embryogenèse chez la mouche. Durant ma thèse j’ai étudié comment Smaug agit sur SMO et la voie HH et aussi comment elle est régulée par HH. J’ai montré que Smaug était un régulateur positif de la voie HH et ce très probablement via sa capacité à fixer des ARNm. J’ai également montré que SMO et Smaug colocalisaient dans des foci cytoplasmiques en absence de signal et que Smaug était relocalisée à la membrane plasmique avec SMO en réponse à HH. Enfin j’ai mis en évidence un effet de SMO et d’HH sur la phosphorylation de Smaug suggérant une potentielle régulation en retour sur l’activité de Smaug. Ce travail m’a permis de proposer à la fois un nouveau rôle de la protéine de liaison aux ARN Smaug dans un processus de signalisation cellulaire ainsi que l’implication jusqu’ici insoupçonnée, d’une possible régulation post-transcriptionnelle d’ARNm dans la voie HH / Hedgehog Proteins (HH) are major players of animal development and carcinogenesis. Their transduction requires the 7 transmembrane protein Smoothened (SMO) whose activity is regulated by Patched (PTC), the HH receptor and antagonist. PTC and HH regulates SMO trafficking, phosphorylation and accumulation but numerous aspects of these regulations remain poorly understood. During my thesis, I focused on Smaug, a new partner of SMO in drosophila which was identified in the laboratory in a yeast two-hybrid screen. Smaug is known to bind and repress numerous mRNA during embryonic development in fly. I analyzed how it acts on SMO and HH signaling and also how is it regulated by HH. I have shown that Smaug is a positive regulator of the HH pathway and that it probably acts via its capacity to bind mRNA. I have also demonstrated that SMO and Smaug colocalise in cytoplasmic foci in absence of signal and that SMO is sufficient to localized Smaug to the plasma membrane in response to HH. Finally, I highlighted an effect of SMO and HH on the phosphorylation of Smaug suggesting the existence of a regulatory loop

In Drosophila, early embryonic development is controlled by maternally loaded RNAs and proteins. For proper development to occur it is vital these maternal transcripts are post-transcriptionally regulated. SMAUG, a major post-transcriptional regulator, has been found to be responsible for the destabilization of two thirds of the unstable maternal transcripts upon egg activation (Tadros et al., 2007). smg mRNA is translationally repressed in stage 14 oocytes, but its translation is activated upon egg activation in a PAN GU kinase dependent manner. Here I show that redundant translational repression elements reside in the smg 3’UTR, and PUMILIO mediates repression through one of these elements. I also show that these elements are sufficient to cause translational repression in stage 14 oocytes. smg mRNA appears to be regulated post-initiation in stage 14 oocytes in a large repression complex which is similar to smg mRNA repression in a png mutant.

In Drosophila, early embryonic development is controlled by maternally loaded RNAs and proteins. For proper development to occur it is vital these maternal transcripts are post-transcriptionally regulated. SMAUG, a major post-transcriptional regulator, has been found to be responsible for the destabilization of two thirds of the unstable maternal transcripts upon egg activation (Tadros et al., 2007). smg mRNA is translationally repressed in stage 14 oocytes, but its translation is activated upon egg activation in a PAN GU kinase dependent manner. Here I show that redundant translational repression elements reside in the smg 3’UTR, and PUMILIO mediates repression through one of these elements. I also show that these elements are sufficient to cause translational repression in stage 14 oocytes. smg mRNA appears to be regulated post-initiation in stage 14 oocytes in a large repression complex which is similar to smg mRNA repression in a png mutant.