Single Cell Transcriptomics Reveals Dysregulated Cellular and Molecular Networks in a Fragile X Syndrome model [preprint]

Despite advances in understanding the pathophysiology of Fragile X syndrome (FXS), its molecular bases are still poorly understood. Whole brain tissue expression profiles have proved surprisingly uninformative. We applied single cell RNA sequencing to profile a FXS mouse model. We found that FXS results in a highly cell type specific effect and it is strongest among different neuronal types. We detected a downregulation of mRNAs bound by FMRP and this effect is prominent in neurons. Metabolic pathways including translation are significantly upregulated across all cell types with the notable exception of excitatory neurons. These effects point to a potential difference in the activity of mTOR pathways, and together with other dysregulated pathways suggest an excitatory-inhibitory imbalance in the FXS cortex which is exacerbated by astrocytes. Our data demonstrate the cell-type specific complexity of FXS and provide a resource for interrogating the biological basis of this disorder

Genetic Rescue of Fragile X Syndrome Links FMRP Deficiency to Codon Optimality-Dependent RNA Destabilization [preprint]

Fragile X syndrome (FXS) is caused by inactivation of FMR1 gene and loss of its encoded product the RNA binding protein FMRP, which generally represses translation of its target transcripts in the brain. In mouse models of FXS (i.e., Fmr1 knockout animals; Fmr1 KO), deletion of Cpeb1, which encodes a translational activator, mitigates nearly all pathophysiologies associated with the disorder. Here we reveal unexpected wide-spread dys-regulation of RNA abundance in Fmr1 KO brain cortex and its rescue to normal levels in Fmr1/Cpeb1 double KO mice. Alteration and restoration of RNA levels are the dominant molecular events that drive the observed dys-regulation and rescue of translation as measured by whole transcriptome ribosome occupany in the brain. The RNAs down-regulated and rescued in these animal models are highly enriched for FMRP binding targets and have an optimal codon bias that would predict their stability in wild type and possible instability in FMRP knock-out brain. Indeed, whole transcriptome analysis of RNA metabolic rates demonstrates a codon optimality-dependent elevation of RNA destruction in FMRP knock-out cortical neurons. This elevated RNA destruction leads to a massive reshuffling of the identities of stabilizing versus destabilizing codons in neurons upon loss of FMRP. Our results show a widespread RNA instability in FXS, which results from the uncoupling of codon optimality, ribosome occupancy, and RNA degradation mechanisms. Re-establishment of the linkage among these events is likely required by the genetic rescue of the disorder

Practical Access to Aromatic Thiocyanates by CuCN-Mediated Direct Aerobic Oxidative Cyanation of Thiophenols and Diaryl Disulfides

International audienceThe practical and mild aerobic oxidative CuCN-mediated cyanation of thiophenols and diaryl disulfides was investigated. The reaction was performed in air at room temperature and reached aromatic thiocyanates in moderate to good yields starting from a broad range of diversely functionalized substrates

Intramolecular inverse electron-demand [4+2] cycloadditions of ynamidyl-tethered pyrimidines: Comparative studies in trifluorotoluene and sulfolane

International audienceThree representative 6,7-dihydro-5H-cyclopenta[b]pyridin-4-amines were synthesized using an intramolecular inverse electron demand heteroeDielseAlder/retroeDielseAlder sequence between pyrimidines (acting as azadienes) and ynamides (acting as dienophiles). Two solvents of this reaction, sulfolane and trifluorotoluene, were compared at 210 C and the former consistently led to higher yields. In addition, these studies confirmed the importance of the steric bulk of the C5-position of the pyrimidinyl cycloaddition precursor

FMRP Links Optimal Codons to mRNA stability in Neurons [preprint]

Fragile X syndrome (FXS) is caused by inactivation of the FMR1 gene and loss of encoded FMRP, an RNA binding protein that represses translation of some of its target transcripts. Here we use ribosome profiling and RNA-seq to investigate the dysregulation of translation in the mouse brain cortex. We find that most changes in ribosome occupancy on hundreds of mRNAs are largely driven by dysregulation in transcript abundance. Many downregulated mRNAs, which are mostly responsible for neuronal and synaptic functions, are highly enriched for FMRP binding targets. RNA metabolic labeling demonstrates that in FMRP-deficient cortical neurons, mRNA downregulation is caused by elevated degradation, and is correlated with codon optimality. Moreover, FMRP preferentially binds mRNAs with optimal codons, suggesting that it stabilizes such transcripts through direct interactions via the translational machinery. Finally, we show that the paradigm of genetic rescue of FXS-like phenotypes in FMRP-deficient mice by deletion of the Cpeb1 gene is mediated by restoration of steady state RNA levels and consequent rebalancing of translational homeostasis. Our data establish an essential role of FMRP in codon optimality-dependent mRNA stability as an important factor in FXS

Comparative study on the reactivity of propargyl and alkynyl sulfides in palladium-catalyzed domino reactions

International audienceThree types of sulfides bearing a propargyl or an alkynyl moiety have been studied in cyclocarbopalladation/cross-coupling domino palladium-catalyzed sequences. The reactivity of different types of sulfured starting materials has been compared as well as the difference in behavior of these compounds depending on the type of cross coupling ending the domino sequence. It appeared that these cascades were constantly more efficient on the propargyl benzyl thioether. In addition, it has been demonstrated that domino sequences ending with Stille, SuzukieMiyaura, or MizorokieHeck lead efficiently and selectively to the desired cyclized products. Notably, when the introduction of an alkyne is targeted at the end of the cascade, it appeared that the Sonogashira coupling leads every time to the desired cyclic product in the mixture with the product resulting from the direct coupling between the aryl moiety of the substrate and the alkyne used as partner. Finishing the domino sequence with a Stille coupling instead of a Sonogashira one allowed improving significantly the ratio of the mixture in favor of the desired cyclized compound

Genes encoding multiple forms of phospholipase A(2) are expressed in immature forms of human leukemic blasts.

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