De bé à bébé : le transfert d'apprentissage auditori-moteur pour interroger l'unité de production de la parole

International audienceSpeech is often described as a sequence of units associating linguistic, sensory and motor representations. Are these representations linked at the level of a specific unit, for example, the syllable or the word? In the present study, we contrast these two hypotheses. We modified the production of the syllable “bé” (/be/) in French speakers using an auditory-motor adaptation paradigm that consists in altering the speakers’ auditory feedback. We studied how this modification then transfers to the production of the word “bébé” (/bebe/). The results suggest a link between linguistic and motor representations both at the word and the syllable level. They also show an effect of the position of the syllable in the transfer word, which raises new interrogations about serialcontrol of speech.La parole est souvent décrite comme une mise en séquence d'unités associant des représentations linguistiques, sensorielles et motrices. Le lien entre ces représentations se fait-il de manière privilégiée sur une unité spécifique ? Par exemple, est-ce la syllabe ou le mot ? Dans cette étude, nous voulons contraster ces deux hypothèses. Pour cela, nous avons modifié chez des locuteurs du français la production de la syllabe « bé », selon un paradigme d'adaptation auditori-motrice, consistant à perturber le retour auditif. Nous avons étudié comment cette modification se transfère ensuite à la production du mot « bébé ». Les résultats suggèrent un lien entre représentations linguistiques et motrices à plusieurs niveaux, à la fois celui du mot et de la syllabe. Ils montrent également une influence de la position de la syllabe dans le mot sur le transfert, qui soulève de nouvelles questions sur le contrôle sériel de la parole

Expression and Transport of a-Synuclein at the Blood-Cerebrospinal Fluid Barrier and Effects of Manganese Exposure

The choroid plexus maintains the homeostasis of critical molecules in the brain by regulating their transport between the blood and cerebrospinal fluid (CSF). The current study was designed to investigate the potential role of the blood-CSF barrier (BCSFB) in α-synuclein (a-Syn) transport in the brain as affected by exposure to manganese (Mn), the toxic metal implicated in Parkinsonian disorders. Immunohistochemistry was used to identify intracellular a-Syn expression at the BCSFB. Quantitative real-time PCR was used to quantify the change in a-Syn mRNA expression following Mn treatments at the BCSFB in vitro. ELISA was used to quantify a-Syn levels following in vivo and in vitro treatments of Mn, copper (Cu), and/or external a-Syn. Thioflavin-T assay was used to investigate a-Syn aggregation after incubating with Mn and/or Cu in vitro. A two-chamber Transwell system was used to study a-Syn transport by BCSFB monolayer.Data revealed the expression of endogenous a-Syn in rat choroid plexus tissue and immortalized choroidal epithelial Z310 cells. The cultured primary choroidal epithelia from rats showed the ability to take up a-Syn from extracellular medium and transport a-Syn across the cellular monolayer from the donor to receiver chamber. Exposure of cells with Mn induced intracellular a-Syn accumulation without causing any significant changes in a-Syn mRNA expression. A significant increase in a-Syn aggregation in a cell-free system was observed with the presence of Mn. Moreover, Mn exposure resulted in a significant uptake of a-Syn by primary cells.These data indicate that the BCSFB expresses a-Syn endogenously and is capable of transporting a-Syn across the BCSFB monolayer; Mn exposure apparently increases a-Syn accumulation in the BCSFB by facilitating its uptake and intracellular aggregation

From Sensorimotor Experience To Speech Unit -Adaptation to altered auditory feedback in speech to assess transfer of learning in complex serial movements

International audienceUsing bird song as a model to understand generalization in motor learning, Hoffman and Sober recently found that adaptation to pitch-shift of birds’ vocal output transfered to the production of the same sounds embedded in a different serial context (J. Neurosc 2014). In humans, speech learning has been found to transfer as a function of the acoustical similarity between the training and the testing utterances (Cai et al. 2010, Rochet-Capellan et al. 2011) but it is unclear if transfer of learning is sensitive to serial order. We investigate the effects of serial order on transfer of speech motor learning using non-words sequences of CV syllables. Three groups of native speakers of French were trained to produce the syllable /be/ repetitively while their auditory feedback was altered in real time toward /ba/. They were then tested for transfer toward /be/ (control), /bepe/ or /pebe/ under normal feedback conditions. The training utterance was then produced again to test for after-effects. The auditory shift was achieved in real time using Audapter software (Cai et al. 2008). Adaptation and transfer effects were quantified in terms of changes in formants frequencies of the vowel /e/, as a function of its position and the preceding consonant in the utterance. Changes in formant frequencies in a direction opposite to the shift were significant for ~80% of the participants. Adaptation was still significant for the three groups in the after-effect block. Transfer effects in the /bepe/ and /pebe/ groups were globally smaller than that of the control group, particularly when the vowel /e/ came after /p/ and/or was in second position in the utterance. Taken together, the results suggest that transfer of speech motor learning is not homogenous and as observed by Hoffman and Sober, depends on the serial context of a sound within the utterance.Cai S, Boucek M, Ghosh SS, Guenther FH, Perkell JS. (2008). A system foronline dynamic perturbation of formant frequencies and results from perturbation of the Mandarin triphthong /iau/. In Proceedings of the 8th Intl. Seminar on Speech Production, Strasbourg, France, Dec. 8-12, 2008. pp. 65Cai, S., Ghosh, S. S., Guenther, F. H., & Perkell, J. S. (2010). Adaptive auditory feedback control of the production of formant trajectories in the Mandarin triphthong/iau/and its pattern of generalization. The Journal of the Acoustical Society of America, 128(4), 2033-2048.Hoffmann, L. A., & Sober, S. J. (2014). Vocal generalization depends on gesture identity and sequence. The Journal of Neuroscience, 34(16), 5564-5574.Rochet-Capellan, A., Richer, L., & Ostry, D. J. (2012). Nonhomogeneous transfer reveals specificity in speech motor learning. Journal of neurophysiology, 107(6), 1711-1717

A novel pathway for amyloids self-assembly in aggregates at nanomolar concentration mediated by the interaction with surfaces.

A limitation of the amyloid hypothesis in explaining the development of neurodegenerative diseases is that the level of amyloidogenic polypeptide in vivo is below the critical concentration required to form the aggregates observed in post-mortem brains. We discovered a novel, on-surface aggregation pathway of amyloidogenic polypeptide that eliminates this long-standing controversy. We applied atomic force microscope (AFM) to demonstrate directly that on-surface aggregation takes place at a concentration at which no aggregation in solution is observed. The experiments were performed with the full-size Aβ protein (Aβ42), a decapeptide Aβ(14-23) and α-synuclein; all three systems demonstrate a dramatic preference of the on-surface aggregation pathway compared to the aggregation in the bulk solution. Time-lapse AFM imaging, in solution, show that over time, oligomers increase in size and number and release in solution, suggesting that assembled aggregates can serve as nuclei for aggregation in bulk solution. Computational modeling performed with the all-atom MD simulations for Aβ(14-23) peptide shows that surface interactions induce conformational transitions of the monomer, which facilitate interactions with another monomer that undergoes conformational changes stabilizing the dimer assembly. Our findings suggest that interactions of amyloidogenic polypeptides with cellular surfaces play a major role in determining disease onset

Effect of Ions on the Organization of Phosphatidylcholine/Phosphatidic Acid Bilayers

AbstractLipid bilayers are two-dimensional fluids. Here, the effect of monovalent ion concentration on the mixing, and consequently the organization, of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) bilayers has been examined. Epifluorescence microscopy was used to visualize the organization. Fluorescence recovery after photobleaching and attenuated total reflection-Fourier transform infrared spectroscopy were used to assess the fluidity of the lipids. At high ionic strength the DOPC and DOPA lipids appear uniformly mixed. Upon lowering the ionic strength, rapid separation is observed. The DOPA-rich regions appear fractal-like and exhibit hysteresis in their properties. The lipids freely exchange between the two regions. These experiments clearly demonstrate the significant effect that electrostatics can have on membrane organization

Effect of spermidine on misfolding and interactions of alpha-synuclein.

Alpha-synuclein (α-Syn) is a 140 aa presynaptic protein which belongs to a group of natively unfolded proteins that are unstructured in aqueous solutions. The aggregation rate of α-Syn is accelerated in the presence of physiological levels of cellular polyamines. Here we applied single molecule AFM force spectroscopy to characterize the effect of spermidine on the very first stages of α-Syn aggregation--misfolding and assembly into dimers. Two α-Syn variants, the wild-type (WT) protein and A30P, were studied. The two protein molecules were covalently immobilized at the C-terminus, one at the AFM tip and the other on the substrate, and intermolecular interactions between the two molecules were measured by multiple approach-retraction cycles. At conditions close to physiological ones at which α-Syn misfolding is a rare event, the addition of spermidine leads to a dramatic increase in the propensity of the WT and mutant proteins to misfold. Importantly, misfolding is characterized by a set of conformations, and A30P changes the misfolding pattern as well as the strength of the intermolecular interactions. Together with the fact that spermidine facilitates late stages of α-Syn aggregation, our data demonstrate that spermidine promotes the very early stages of protein aggregation including α-Syn misfolding and dimerization. This finding suggests that increased levels of spermidine and potentially other polyamines can initiate the disease-related process of α-Syn

Direct Detection of α-Synuclein Dimerization Dynamics: Single-Molecule Fluorescence Analysis

AbstractThe aggregation of α-synuclein (α-Syn) is linked to Parkinson’s disease. The mechanism of early aggregation steps and the effect of pathogenic single-point mutations remain elusive. We report here a single-molecule fluorescence study of α-Syn dimerization and the effect of mutations. Specific interactions between tethered fluorophore-free α-Syn monomers on a substrate and fluorophore-labeled monomers diffusing freely in solution were observed using total internal reflection fluorescence microscopy. The results showed that wild-type (WT) α-Syn dimers adopt two types of dimers. The lifetimes of type 1 and type 2 dimers were determined to be 197 ± 3 ms and 3334 ± 145 ms, respectively. All three of the mutations used, A30P, E46K, and A53T, increased the lifetime of type 1 dimer and enhanced the relative population of type 2 dimer, with type 1 dimer constituting the major fraction. The kinetic stability of type 1 dimers (expressed in terms of lifetime) followed the order A30P (693 ± 14 ms) > E46K (292 ± 5 ms) > A53T (226 ± 6 ms) > WT (197 ± 3 ms). Type 2 dimers, which are more stable, had lifetimes in the range of several seconds. The strongest effect, observed for the A30P mutant, resulted in a lifetime 3.5 times higher than observed for the WT type 1 dimer. This mutation also doubled the relative fraction of type 2 dimer. These data show that single-point mutations promote dimerization, and they suggest that the structural heterogeneity of α-Syn dimers could lead to different aggregation pathways

Hsp31 Is a Stress Response Chaperone That Intervenes in the Protein Misfolding Process

The Saccharomyces cerevisiae heat shock protein Hsp31 is a stress-inducible homodimeric protein that is involved in diauxicshift reprogramming and has glyoxalase activity. We show thatsubstoichiometric concentrations of Hsp31 can abrogate aggrega-tion of a broad array of substrates in vitro. Hsp31 also modulates the aggregation of -synuclein ( Syn), a target of the chaperoneactivity of human DJ-1, an Hsp31 homolog. We demonstrate thatHsp31 is able to suppress the in vitro fibrillization or aggregation of Syn, citrate synthase and insulin. Chaperone activity was also observed in vivo because constitutive overexpression of Hsp31 reduced the incidence of Syn cytoplasmic foci, and yeast cells were rescued from Syn-generated proteotoxicity upon Hsp31overexpression. Moreover, we showed that Hsp31 protein levels are increased byH2O2, in the diauxic phase of normal growth con-ditions, and in cells under Syn-mediated proteotoxic stress. Weshow that Hsp31 chaperone activity and not the methylglyoxalaseactivity or the autophagy pathway drives the protective effects.Wealso demonstrate reduced aggregation of the Sup35 prion domain,PrD-Sup35, as visualized by fluorescent protein fusions. In addi-tion, Hsp31 acts on its substrates prior to the formation of largeaggregates because Hsp31 does not mutually localize with prionaggregates, and it prevents the formation of detectable in vitro Syn fibrils. These studies establish that the protective role ofHsp31 against cellular stress is achieved by chaperone activity thatintervenes early in the protein misfolding process and is effectiveona wide spectrum of substrate proteins, including Synandprion proteins

Cyclin-G-associated kinase modifies alpha-synuclein expression levels and toxicity in Parkinson's disease: results from the GenePD Study

Although family history is a well-established risk factor for Parkinson's disease (PD), fewer than 5% of PD cases can be attributed to known genetic mutations. The etiology for the remainder of PD cases is unclear; however, neuronal accumulation of the protein α-synuclein is common to nearly all patients, implicating pathways that influence α-synuclein in PD pathogenesis. We report a genome-wide significant association (P = 3.97 × 10−8) between a polymorphism, rs1564282, in the cyclin-G-associated kinase (GAK) gene and increased PD risk, with a meta-analysis odds ratio of 1.48. This association result is based on the meta-analysis of three publicly available PD case–control genome-wide association study and genotyping from a new, independent Italian cohort. Microarray expression analysis of post-mortem frontal cortex from PD and control brains demonstrates a significant association between rs1564282 and higher α-synuclein expression, a known cause of early onset PD. Functional knockdown of GAK in cell culture causes a significant increase in toxicity when α-synuclein is over-expressed. Furthermore, knockdown of GAK in rat primary neurons expressing the A53T mutation of α-synuclein, a well-established model for PD, decreases cell viability. These observations provide evidence that GAK is associated with PD risk and suggest that GAK and α-synuclein interact in a pathway involved in PD pathogenesis. The GAK protein, a serine/threonine kinase, belongs to a family of proteins commonly targeted for drug development. This, combined with GAK's observed relationship to the levels of α-synuclein expression and toxicity, suggests that the protein is an attractive therapeutic target for the treatment of PD.Robert P. & Judith N. Goldberg FoundationWilliam N. & Bernice E. Bumpus FoundationHoward Hughes Medical Institute (Collaborative Innovation Award)National Science Foundation (U.S.) (R01-NS036711