Mécanismes et conséquences des mutations

L’identification des mutations à l’origine de maladies génétiques chez l’homme a pris ces dernières années un essor considérable. Il est devenu possible d’établir le spectre des mutations délétères pour une maladie génétique donnée, et des bases de données internationales sont aujourd’hui accessibles via le réseau Internet. Le diagnostic génotypique des maladies héréditaires occupe actuellement une place prépondérante en matière de conseil génétique et de diagnostic prénatal. La connaissance du type de mutation délétère et des mécanismes en cause est essentielle pour déterminer la stratégie de diagnostic moléculaire adaptée à chaque situation. Cet article a pour objectif de présenter les différents types de mutations responsables de maladies génétiques (substitutions nucléotidiques, délétions ou insertions de petite taille, mutations dynamiques, grands remaniements…) et de récapituler les connaissances actuelles concernant les mécanismes moléculaires à l’origine de ces mutations. Leurs conséquences sur l’expression du gène (transcription et maturation du transcrit) et sur la fonction de la protéine sont également abordées dans cet article.The identification of mutations leading to human genetic diseases has grown into an intensive research field during the last few years. Through novel DNA analysis progress, it is now possible to determine the mutational spectrum for a given genetic disease and international databases are now available online. Genetic diagnosis of hereditary diseases has become an essential tool in genetic counselling and prenatal diagnosis. The knowledge of the deleterious mutation type and the molecular associated mechanism is fundamental in order to devise the optimal molecular diagnosis strategy. This review aims to present the various mutation categories involved in genetic diseases (single base-pair substitutions, small deletions or insertions, dynamic mutations, gross DNA lesions…) and to summarize our current knowledge about the main molecular mechanisms responsible for these mutations. Their deleterious consequences on gene expression, including transcription and transcript maturation, and protein loss or gain of function are also discussed in this review

Molecular profiling of malignant peripheral nerve sheath tumors associated with neurofibromatosis type 1, based on large-scale real-time RT-PCR

BACKGROUND: Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a complex range of clinical symptoms. The hallmark of NF1 is the onset of heterogeneous (dermal or plexiform) benign neurofibromas. Plexiform neurofibromas can give rise to malignant peripheral nerve sheath tumors (MPNSTs), and the underlying molecular mechanisms are largely unknown. RESULTS: To obtain further insight into the molecular pathogenesis of MPNSTs, we used real-time quantitative RT-PCR to quantify the mRNA expression of 489 selected genes in MPNSTs, in comparison with plexiform neurofibromas. The expression of 28 (5.7%) of the 489 genes was significantly different between MPNSTs and plexiform neurofibromas; 16 genes were upregulated and 12 were downregulated in MPNSTs. The altered genes were mainly involved in cell proliferation (MKI67, TOP2A, CCNE2), senescence (TERT, TERC), apoptosis (BIRC5/Survivin, TP73) and extracellular matrix remodeling (MMP13, MMP9, TIMP4, ITGB4). More interestingly, other genes were involved in the Ras signaling pathway (RASSF2, HMMR/RHAMM) and the Hedgehog-Gli signaling pathway (DHH, PTCH2). Several of the down-regulated genes were Schwann cell-specific (L1CAM, MPZ, S100B, SOX10, ERBB3) or mast cell-specific (CMA1, TPSB), pointing to a depletion and/or dedifferentiation of Schwann cells and mast cells during malignant transformation of plexiform neurofibromas. CONCLUSION: These data suggest that a limited number of signaling pathways, and particularly the Hedgehog-Gli signaling pathway, may be involved in malignant transformation of plexiform neurofibromas. Some of the relevant genes or their products warrant further investigation as potential therapeutic targets in NF1

Overexpression of copper zinc superoxide dismutase impairs human trophoblast cell fusion and differentiation.: SOD-1 and Human Trophoblast Differentiation

The syncytiotrophoblast is the major component of the human placenta, involved in feto-maternal exchanges and secretion of pregnancy-specific hormones. Multinucleated syncytiotrophoblast arises from fusion of mononuclear cytotrophoblast cells. In trisomy 21-affected placentas, we recently have shown that there is a defect in syncytiotrophoblast formation and a decrease in the production of pregnancy-specific hormones. Due to the role of oxygen free radicals in trophoblast cell differentiation, we investigated the role of the key antioxidant enzyme, copper/zinc superoxide dismutase, encoded by chromosome 21 in in vitro trophoblast differentiation. We first observed that overexpression of superoxide dismutase in normal cytotrophoblasts impaired syncytiotrophoblast formation. This was associated with a significant decrease in mRNA transcript levels and secretion of hCG and other hormonal markers of syncytiotrophoblast. We confirmed abnormal cell fusion by overexpression of green fluorescence protein-tagged superoxide dismutase in cytotrophoblasts. In addition, a significant decrease in syncytin transcript levels was observed in superoxide dismutase-transfected cells. We then examined superoxide dismutase expression and activity in isolated trophoblast cells from trisomy 21-affected placentas. Superoxide dismutase mRNA expression (P < 0.05), protein levels (P < 0.01), and activity (P < 0.05) were significantly higher in trophoblast cells isolated from trisomy 21-affected placentas than in those from normal placentas. These results suggest that superoxide dismutase overexpression may directly impair trophoblast cell differentiation and fusion, and superoxide dismutase overexpression in Down's syndrome may be responsible at least in part for the failure of syncytiotrophoblast formation observed in trisomy 21-affected placentas

Porcine neurofibromatosis : a new syndrome

A genetically dominant neoplasic disease similar to human neurofibromatosis has just been discovered in pigs. Two of the three clinical forms known in man have been identified in several pig farms: one with large subcutaneous tumours, the other exclusively intradermal. Clinical and pathology studies have been performed on these lesions. Tumour cells are being cultured and the sequencing of their genome is underway. This research is especially important because no animal model of this very common disease in man was available until now.Une affection tumorale similaire à la neurofibromatose de l'Homme vient d'être découverte chez le porc. Cette maladie, de caractère génétique dominant, a été retrouvée dans plusieurs élevages sous deux des trois formes rencontrées chez l'Homme, l'une à grosses tumeurs sous-cutanées et l'autre, strictement intradermique. Ces lésions ont été étudiées aux plans clinique et anatomopathologique. Les cellules tumorales ont été mises en culture et le séquençage de leur génome entrepris. Ce travail revêt une importance toute particulière car il n'existait jusqu'alors aucun modèle animal de cette maladie très fréquente chez l'Homme

Frequent EGFR Positivity and Overexpression in High-Grade Areas of Human MPNSTs

Malignant peripheral nerve sheath tumours (MPNSTs) are highly malignant and resistant. Transformation might implicate up regulation of epidermal growth factor receptor (EGFR). Fifty-two MPNST samples were studied for EGFR, Ki-67, p53, and survivin expression by immunohistochemistry and for EGFR amplification by in situ hybridization. Results were correlated with clinical data. EGFR RNA was also quantified by RT-PCR in 20 other MPNSTs and 14 dermal neurofibromas. Half of the patients had a neurofibromatosis type 1 (NF1). EGFR expression, detected in 86% of MPNSTs, was more frequent in NF1 specimens and closely associated with high-grade and p53-positive areas. MPNSTs expressed more EGFR transcripts than neurofibromas. No amplification of EGFR locus was observed. NF1 status was the only prognostic factor in multivariate analysis, with median survivals of 18 and 43 months for patients with or without NF1. Finally, EGFR might become a new target for MPNSTs treatment, especially in NF1-associated MPNSTs

Neurofibromatose de type 1 (du génotype au phénotype)

PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

Génétique moléculaire des tumeurs bénignes et malignes des gaines nerveuses périphériques chez les patients atteints de neurofibromatose de type 1

Avec une incidence estimée à une naissance sur 3500 la neurofibromatose de type 1 est l une des maladies génétiques à transmission autosomique dominante les plus fréquentes. Les signes cliniques sont très variables même au sein d une famille ; cependant la présence de neurofibromes, tumeurs bénignes des gaines nerveuses périphériques, reste pathognomonique de cette maladie. Il est classique de distinguer les neurofibromes cutanés des neurofibromes plexiformes qui seuls peuvent se transformer en tumeurs malignes des gaines nerveuses (MPNST) ou neurofibrosarcomes, de très mauvais pronostic. Les mutations du gène NF1 à l origine de la maladie sont très hétérogènes et, à ce jour, aucune relation génotype-phénotype n a pu être démontrée. De même, les mécanismes moléculaires régulant le développement et l évolution des neurofibromes chez les patients restent à élucider. Dans cette optique, nous avons réalisé une analyse ciblée puis à grande échelle du transcriptome de neurofibromes plexiformes et de neurofibrosarcomes ainsi que l étude de l expression d une quinzaine de gènes localisés à proximité du gène NF1 et délétés avec ce dernier dans les syndromes microdélétionnels. Les résultats obtenus nous ont permis de définir une signature moléculaire constituée de 5 gènes prédictive du risque d évolution vers la malignité des neurofibromes plexiformes et d identifier un certain nombre de voies et de gènes plus particulièrement impliqués dans la genèse des neurofibromes plexiformes et leur transformation en MPNSTs apportant ainsi de nouvelles données permettant d envisager la mise en place de thérapeutiques ciblées.NF1 is one of the most common autosomal dominant disorder occurring in man, affecting 1 in every 3,500 newborn infants.The hallmarks of NF1 vary widely even within a family but the presence of neurofibromas, benign peripheral nerve sheaths tumors, remains pathognomonic of the disease. It is traditional to distinguish cutaneous neurofibromas and plexiform neurofibromas which alone can progress to malignant peripheral nerve sheaths tumor (MPNST) also known as neurofibrosarcoma with a very poor prognosis.The NF1 gene mutations causing the disease are very heterogeneous and, to date, no genotype-phenotype relationship has been demonstrated.The molecular mechanisms that regulate the development and evolution of neurofibromas in patients remain unclear.In this context, we conducted targeted and large-scale analysis over Plexiform neurofibromas and neurofibrosarcoma s transcriptome. We also studied expression of a fortnight of genes located near the NF1 deleted gene and with it the microdeletional syndromes. The results have enabled us to define a molecular signature of 5 genes predictive of the risk of Plexiform neurofibromas progression to malignancy and identify a number of pathways and genes specifically involved in the genesis of Plexiform neurofibromas and MPNSTs transformation thus providing new data to consider the introduction of targeted therapiesPARIS-BIUP (751062107) / SudocSudocFranceF

Physiopathologie de la neurofibromatose de type 1

PARIS-BIUP (751062107) / SudocSudocFranceF

Approches pour l'identification de modificateurs génétiques (à propos de la neurofibromatose de type 1)

PARIS-BIUP (751062107) / SudocSudocFranceF