Engrailed and polyhomeotic maintain posterior cell identity through cubitus-interruptus regulation

AbstractIn Drosophila, the subdivision into compartments requires the expression of engrailed (en) and hedgehog (hh) in the posterior cells and of cubitus-interruptus (ci) in the anterior cells. Whereas posterior cells express hh, only anterior cells are competent to respond to the hh signal, because of the presence of ci expression in these cells. We show here that engrailed and polyhomeotic (ph), a member of the Polycomb Group (PcG) genes, act concomitantly to maintain the repression of ci in posterior compartments during development. Using chromatin immunoprecipitation (ChIP), we identified a 1 kb genomic fragment located 4 kb upstream of the ci coding region that is responsible for the regulation of ci. This genomic fragment is bound in vivo by both Polyhomeotic and Engrailed. In particular, we show that Engrailed is responsible for the establishment of ci repression early during embryonic development and is also required, along with Polyhomeotic, to maintain the repression of ci throughout development

A Concerted Action of Engrailed and Gooseberry-Neuro in Neuroblast 6-4 Is Triggering the Formation of Embryonic Posterior Commissure Bundles

One challenging question in neurogenesis concerns the identification of cues that trigger axonal growth and pathfinding to form stereotypic neuronal networks during the construction of a nervous system. Here, we show that in Drosophila, Engrailed (EN) and Gooseberry-Neuro (GsbN) act together as cofactors to build the posterior commissures (PCs), which shapes the ventral nerve cord. Indeed, we show that these two proteins are acting together in axon growth and midline crossing, and that this concerted action occurs at early development, in neuroblasts. More precisely, we identified that their expressions in NB 6-4 are necessary and sufficient to trigger the formation of the PCs, demonstrating that segmentation genes such as EN and GsbN play a crucial role in the determination of NB 6-4 in a way that will later influence growth and guidance of all the axons that form the PCs. We also demonstrate a more specific function of GsbN in differentiated neurons, leading to fasciculations between axons, which might be required to obtain PC mature axon bundles

Caractérisation des éléments de réponse à l'homéoprotéine Engrailed et aux facteurs du groupe "Polycomb" au sein des gènes "cubitus interruptus "et "hedgehog" chez "Drosophila melanogaster"

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

The P42 peptide and Peptide-based therapies for Huntington’s disease

International audienceHuntington’s disease (HD) is a progressive neurodegenerative hereditary disease clinically characterised by the presence of involuntary movements, behavioural problems and cognitive decline. The disease-onset is usually between 30 and 50 years of age. HD is a rare disorder affecting approximately 1.3 in 10,000 people in the European Union. It is caused by an expanded CAG repeat in the first exon of the Huntingtin (HTT) gene, leading to an abnormal form of the Huntingtin protein (Htt) (polyQHtt), containing N-terminus, enlarged polyglutamine strands of variable length that stick together to form aggregates and nuclear inclusions in the damaged brain cells. Treatments currently used for Huntington’s disease are symptomatic and aimed at temporally relieving the symptoms of the disease; although some promising therapies are on study, there is no drug capable of stopping disease progression either in the form of delaying onset or slowing disability progression. The utilization of peptides interacting with polyQ stretches or with Htt protein to prevent misfolding and aggregation of the expanded polyQ protein is a fascinating idea, because of low potential toxicity and ability to target very initial steps in the pathophysiological cascade of the disease, such as aggregation or cleavage process. Indeed, several therapeutic peptides have been developed and were found to significantly slow down the progression of symptoms in experimental models of Huntington’s disease. This review is essentially focusing on the latest development concerning peptide strategy. In particular, we focused on a 23aa peptide P42, which is a part of the Htt protein. It is expected to work principally by preventing the abnormal Htt protein from sticking together, thereby preventing pathological consequences of aggregation and improving the symptoms of the disease. In the meantime, as P42 is part of the Htt protein, some therapeutic properties might be linked to the physiological actions of the peptide itself, considered as a functional domain of the Htt protein

Régulation de l'expression de frazzled par Engrailed au cours de la neurogenèse (mise en évidence d'une nouvelle fonction de Frazzled dans la morphogenèse de l'aile et identification de nouveaux partenaires d'Engrailed chez la Drosophile)

Chez la Drosophile, la corde neurale ventrale (VNC) s établit à partir des neuroblastes qui sont spécifiés au cours du développement embryonnaire, par un grand nombre de facteurs de transcription. Engrailed participe à la spécification des neuroblastes et nous avons montré qu il participait également au guidage axonal des neurones issus de ces neuroblastes. Les mutants engrailed présentent une perte des commissures postérieures (PC) alors que la surexpression précoce d Engrailed, avant la formation des neurones, conduit à des défauts de guidage. L analyse des interactions entre engrailed, frazzled, trio et enabled, qui sont tous impliqués dans le guidage axonal, montre qu ils interagissent avec engrailed dans la formation de la VNC. Nous avons également montré que la régulation de frazzled dans les neuroblastes qui expriment Engrailed était très importante pour la formation des PC, en agissant probablement sur la croissance des axones. De plus, nous avons identifié un fragment génomique dans l intron 1 de frazzled, qui, en fusion avec la GFP, est capable de répondre à Engrailed in vivo. En parallèle, nous avons mis en évidence un nouveau rôle de Frazzled. Frazzled intervient dans la morphogenèse de l aile pupale, probablement en jouant le rôle de protéine d adhésion pour l accolement des feuillets alaires dorsaux et ventraux. DSRF et frazzled interagissent dans ce mécanisme et DSRF semble réguler l expression de Frazzled pendant les stades tardifs de la morphogenèse de l aile. Enfin, un crible double hybride a permis l identification de sept nouveaux partenaires d Engrailed dont quatre sont impliqués dans le contrôle de la transcriptionDuring Drosophila embryogenesis, Engrailed (En) is involved in the specification of neuroblasts and we show that it is also involved in axonal guidance of neurons born from these neuroblasts. Whereas en mutant embryos show a lack of posterior commissures (PC), embryos overexpressing En at early stages show guidance defects. We have shown that frazzled (fra), trio and enabled interact genetically with en for the formation of the ventral nerve cord. We have also shown that fra regulation in Engrailed-expressing neuroblasts was important for the formation of PC. A new role of Fra was also discovered in pupal wing morphogenesis, probably through a cell-cell adhesion molecule manner, for the correct apposition of the dorsal and ventral wing layers. DSRF and fra interact in this mechanism and DSRF probably regulates Fra expression during the late stages of wing morphogenesis. Moreover, with a two hybrid screen, we have identified 7 new En partnersMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Mutant huntingtin-impaired degradation of β-catenin causes neurotoxicity in Huntington's disease

Huntington's disease (HD) is a fatal neurodegenerative disorder causing selective neuronal death in the brain. Dysfunction of the ubiquitin–proteasome system may contribute to the disease; however, the exact mechanisms are still unknown. We report here a new pathological mechanism by which mutant huntingtin specifically interferes with the degradation of β-catenin. Huntingtin associates with the β-catenin destruction complex that ensures its equilibrated degradation. The binding of β-catenin to the destruction complex is altered in HD, leading to the toxic stabilization of β-catenin. As a consequence, the β-transducin repeat-containing protein (β-TrCP) rescues polyglutamine (polyQ)-huntingtin-induced toxicity in striatal neurons and in a Drosophila model of HD, through the specific degradation of β-catenin. Finally, the non-steroidal anti-inflammatory drug indomethacin that decreases β-catenin levels has a neuroprotective effect in a neuronal model of HD and in Drosophila and increases the lifespan of HD flies. We thus suggest that restoring β-catenin homeostasis in HD is of therapeutic interest

A huntingtin peptide inhibits polyQ-huntingtin associated defects

BACKGROUND: Huntington's disease (HD) is caused by the abnormal expansion of the polyglutamine tract in the human Huntingtin protein (polyQ-hHtt). Although this mutation behaves dominantly, huntingtin loss of function also contributes to HD pathogenesis. Indeed, wild-type Huntingtin plays a protective role with respect to polyQ-hHtt induced defects. METHODOLOGY/PRINCIPAL FINDINGS: The question that we addressed here is what part of the wild-type Huntingtin is responsible for these protective properties. We first screened peptides from the Huntingtin protein in HeLa cells and identified a 23 aa peptide (P42) that inhibits polyQ-hHtt aggregation. P42 is part of the endogenous Huntingtin protein and lies within a region rich in proteolytic sites that plays a critical role in the pathogenesis process. Using a Drosophila model of HD, we tested the protective properties of this peptide on aggregation, as well as on different polyQ-hHtt induced neuronal phenotypes: eye degeneration (an indicator of cell death), impairment of vesicular axonal trafficking, and physiological behaviors such as larval locomotion and adult survival. Together, our results demonstrate high protective properties for P42 in vivo, in whole animals. These data also demonstrate a specific role of P42 on Huntington's disease model, since it has no effect on other models of polyQ-induced diseases, such as spinocerebellar ataxias. CONCLUSIONS/SIGNIFICANCE: Altogether our data show that P42, a 23 aa-long hHtt peptide, plays a protective role with respect to polyQ-hHtt aggregation as well as cellular and behavioral dysfunctions induced by polyQ-hHtt in vivo. Our study also confirms the correlation between polyQ-hHtt aggregation and neuronal defects. Finally, these results strongly suggest a therapeutic potential for P42, specific of Huntington's disease