IDH1 or IDH2 mutations predict longer survival and response to temozolomide in low-grade gliomas.

OBJECTIVES: Recent studies have shown that IDH1 and IDH2 mutations occur frequently in gliomas, including low-grade gliomas. However, their impact on the prognosis and chemosensitivity of low-grade gliomas remains unclear. METHODS: Search for IDH1 and IDH2 mutations, loss of heterozygosity on chromosomes 1p and 19q, MGMT promoter methylation, and p53 expression was performed in a series of 271 low-grade gliomas and correlated with overall survival. A subgroup of 84 patients treated up-front with temozolomide was individualized. Response to temozolomide was evaluated by progression-free survival, as well as by tumor size on successive MRI scans, and then correlated with molecular alterations. RESULTS: IDH (IDH1 or IDH2) mutations were found in 132/189 patients (70%). IDH mutation and 1p-19q codeletion were associated with prolonged overall survival in univariate (p = 0.002 and p = 0.0001) and multivariate analysis (p = 0.003 and p = 0.004). 1p-19q codeletion, MGMT promoter methylation, and IDH mutation (p = 0.01) were correlated with a higher rate of response to temozolomide. Further analysis of the course of the disease prior to any treatment except for surgery (untreated subgroup) showed that 1p-19q codeletion was associated with prolonged progression-free survival in univariate analysis, whereas IDH mutation was not. CONCLUSION: IDH mutation appears to be a significant marker of positive prognosis and chemosensitivity in low-grade gliomas, independently of 1p-19q codeletion, whereas its impact on the course of untreated tumors seems to be limited.

All the 1p19q codeleted gliomas are mutated on IDH1 or IDH2.

BACKGROUND: Recently, the gene encoding the human cytosolic NADPH-dependent isocitrate dehydrogenase (IDH1) was reported frequently mutated in gliomas. Rare mutations were also found in the sequence of the mitochondrial isoform IDH2. METHODS: In a series of 764 gliomas genome-wide characterized, we determined the presence of mutations in the sequences of both IDH1 and IDH2 genes by direct sequencing. RESULTS: We found that all tumors with complete 1p19q codeletion (n = 128) were mutated in the IDH1 (118) or IDH2 (10) gene. This 100% mutation rate contrasted strikingly with other gliomas exhibiting either variable 1p and 19q alterations (n = 159, IDH1/IDH2 mutation rate of 33%) or no 1p19q alteration (n = 477, IDH1/IDH2 mutation rate 32%). Our data also confirm the prognostic impact of IDH1/IDH2 mutation in gliomas whatever grade considered: patients harboring mutations of IDH1/IDH2 have an improved median overall survival. Moreover, in WHO grade II and III gliomas, 3 groups with significantly different outcomes were identified according to their 1p19q and IDH1/IDH2 statuses. Tumors carrying both alterations had longer overall survival than their nonmutated counterpart. CONCLUSIONS: This exclusive association suggests a new mechanism of tumorigenesis. Perhaps the IDH1/IDH2 mutation is a prerequisite for the occurrence of the t(1;19) translocation, or it is required for the 1p19q codeleted cells to acquire a tumor phenotype.

Increased NR2A expression and prolonged decay of NMDA-induced calcium transient in cerebellum of TgDyrk1A mice, a mouse model of Down syndrome.

Transgenic mice overexpressing Dyrk1A (TgDyrk1A), a Down syndrome (DS) candidate gene, exhibit motor and cognitive alterations similar to those observed in DS individuals. To gain new insights into the molecular consequences of Dyrk1A overexpression underlying TgDyrk1A and possibly DS motor phenotypes, microarray studies were performed. Transcriptome analysis showed an upregulation of the NR2A subunit of the NMDA type of glutamate receptors in TgDyrk1A cerebellum. NR2A protein overexpression was also detected in TgDyrk1A cerebellar homogenates, in the synaptosome-enriched fraction and in TgDyrk1A primary cerebellar granular neuronal cultures (CGNs). In TgDyrk1A synaptosomes, calcium-imaging experiments showed a higher calcium uptake after NMDA stimulation. Similarly, NMDA administration promoted longer calcium transients in TgDyrk1A CGNs. Taken together, these results show that NMDA-induced calcium rise is altered in TgDyrk1A cerebellar neurons and indicate that calcium signaling is dysregulated in TgDyrk1A mice cerebella. These findings suggest that DYRK1A overexpression might contribute to the dysbalance in the excitatory transmission found in the cerebellum of DS individuals and DS mouse models.

Transmembrane protein 50b (C21orf4), a candidate for Down syndrome neurophenotypes, encodes an intracellular membrane protein expressed in the rodent brain.

Transmembrane protein 50b, Tmem50b, previously referred to as C21orf4, encodes a predicted transmembrane protein and is one of few genes significantly over-expressed during cerebellar development in a Down syndrome mouse model, Ts1Cje. In order to assess potential mechanisms by which Tmem50b could contribute to Down syndrome-related phenotypes, we determined the expression patterns of Tmem50b mRNA, as well as Tmem50b protein distribution, expression and subcellular localization. In situ hybridization in mice at embryonic day 14.5 showed cortical plate and spinal cord mRNA expression. By postnatal day 7, strong mRNA expression was seen in the cerebellum, hippocampus and olfactory bulb, with diffuse cortical expression. Quantitative PCR of adult mouse tissue showed Tmem50b mRNA expression in the brain, heart and testis. A rabbit polyclonal antibody was generated against Tmem50b and rat and mouse tissue screening by Western blot, and immunohistochemistry showed that protein expression concurred with mRNA expression. Double immunofluorescence revealed that Tmem50b is highly expressed in rat and mouse glial fibrillary acidic protein-positive cells in vivo and in vitro, but less so in neuronal MAP2- or beta-tubulin II-positive cells in vitro. Tmem50b is invariably expressed in cultured mouse neural precursor cells. In adult mouse cerebellum sections, Tmem50b immunoreactivity was found in Purkinje and Golgi cell somata and in Bergmann glial processes. Electron microscopy confirmed that Tmem50b was present on endoplasmic reticulum (ER) and Golgi apparatus membranes. Results indicate that Tmem50b is a developmentally-regulated intracellular ER and Golgi apparatus membrane protein that may prove important for correct brain development through functions associated with precursor cells and glia.

Transcriptional disruptions in Down syndrome: a case study in the Ts1Cje mouse cerebellum during post-natal development.

To understand the aetiology and the phenotypic severity of Down syndrome, we searched for transcriptional signatures in a substructure of the brain (cerebellum) during post-natal development in a segmental trisomy 16 model, the Ts1Cje mouse. The goal of this study was to investigate the effects of trisomy on changes in gene expression across development time. The primary gene-dosage effect on triplicated genes (approximately 1.5) was observed at birth [post-natal day 0 (P0)], at P15 and P30. About 5% of the non-triplicated genes were significantly differentially expressed between trisomic and control cerebellum, while 25% of the transcriptome was modified during post-natal development of the cerebellum. Indeed, only 165, 171 and 115 genes were dysregulated in trisomic cerebellum at P0, P15 and P30, respectively. Surprisingly, there were only three genes dysregulated in development and in trisomic animals in a similar or opposite direction. These three genes (Dscr1, Son and Hmg14) were, quite unexpectedly, triplicated in the Ts1Cje model and should be candidate genes for understanding the aetiology of the phenotype observed in the cerebellum.

Comparative analysis of two 14-3-3 homologues and their expression pattern in the root-knot nematode Meloidogyne incognita.

14-3-3 proteins are highly conserved ubiquitous proteins found in all eukaryotic organisms. They are involved in various cellular processes including signal transduction, cell-cycle control, apoptosis, stress response and cytoskeleton organisation. We report here the cloning of two genes encoding 14-3-3 isoforms from the plant parasitic root-knot nematode Meloidogyne incognita, together with an analysis of their expression. Both genes were shown to be transcribed in unhatched second stage larvae, infective second stage larvae, adult males and females. The Mi-14-3-3-a gene was shown to be specifically transcribed in the germinal primordium of infective larvae, whereas Mi-14-3-3-b was transcribed in the dorsal oesophageal gland in larvae of this stage. The MI-14-3-3-B protein was identified by mass spectrometry in in vitro-induced stylet secretions from infective larvae. The stability and distribution of MI-14-3-3 proteins in host plant cells was assessed after stable expression of the corresponding genes in tobacco BY2 cells.