Etude de l'activation et de l'inactivation pH-dépendantes des canaux ASICs (Acide-Sensing Ion Channels)

RESUME: Etude de l'activation et de l'inactivation pH-dépendantes des canaux ASICs (Acid-Sensing Ion Channels) Benoîte BARGETON, Département de Pharmacologie et de Toxicologie, Université de Lausanne, rue du Bugnon 27, CH-1005 Lausanne, Suisse Les canaux sodiques ASICs (Acid-Sensing Ion Channels) participent à la signalisation neuronale dans les systèmes nerveux périphérique et central. Ces canaux non voltage dépendants sont impliqués dans l'apprentissage, l'expression de la peur, la neurodégénération consécutive à une attaque cérébrale et la douleur. Les bases moléculaires sous-tendant leur activité ne sont pas encore totalement comprises. Ces canaux sont activés par une acidification du milieu extracellulaire et régulés, entre autres, par des ions tels que le Ca2+, le Zn2+ et le CI". La cristallisation de ASIC inactivé a été publiée. Le canal est un trimére de sous-unités identiques ou homologues. Chaque sous-unité a été décrite en analogie à un avant bras, un poignet et une main constituée d'un pouce, d'un doigt, d'une articulation, une boule β et une paume. Nous avons appliqué une approche bioinformatique systématique pour identifier les pH senseurs putatifs de ASICIa. Le rôle des pH senseurs putatifs a été testé par mutagénèse dirigée et des modifications chimiques combinées à une analyse fonctionnelle afin de comprendre comment les variations de ρ H ouvrent ces canaux. Les pH senseurs sont des acides aspartiques et glutamiques éparpillés sur la boucle extracellulaire suggérant que les changements de pH contrôlent l'activation et l'inactivation de ASIC en (dé)protonant ces résidus en divers endroits de la protéine. Par exemple lors de l'activation, la protonation des résidus à l'interface entre le pouce, la boule β et le doigt d'une même sous-unité induit un mouvement du pouce vers la bouie β et le doigt. De même lors de l'inactivation du canal les paumes des trois sous-unités formant une cavité se rapprochent. D'après notre approche bioinformatique, aucune histidine n'est impliquée dans la détection des variations de pH extracellulaire c'est-à-dire qu'aucune histidine ne serait un pH-senseur. Deux histidines de ASIC2a lient le Zn2+ et modifient l'affinité apparente du canal pour les protons. Une seule des deux est conservée parmi tous les ASICs, hASICIa H163. Elle forme un réseau de liaison hydrogène avec ses voisins conservés. L'étude détaillée de ce domaine, Pinterzone, montre son importance dans l'expression fonctionnelle des canaux. La perturbation de ce réseau par l'introduction d'un résidu hydrophobe (cystéine) par mutagénèse dirigée diminue l'expression du canal à la membrane plasmique. La modification des cystéines introduites par des réactifs spécifiques aux groupements sulfhydryle inhibe les canaux mutés en diminuant leur probabilité d'ouverture. Ces travaux décrivent les effets de l'acidification du milieu extracellulaire sur les canaux ASICs. ABSTRACT: Study of pH-dependent activation and inactivation of ASIC channels Benoîte BARGETON, Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1G05 Lausanne, Switzerland The ASIC (Acid-Sensing Ion Channels) sodium channels are involved in neuronal signaling in the central and peripheral nervous system. These non-voltage-gated channels are involved in learning, the expression of fear, neurodegeneration after ischemia and pain sensation. The molecular bases underlying their activity are not yet fully understood. ASICs are activated by extracellular acidification and regulated, eg by ions such as Ca2+, the Zn2+ and CI". The crystallization of inactivated ASIC has been published. The channel is a trimer of identical or homologous subunits. Each subunit has been described in analogy to a forearm, wrist and hand consisting of a thumb, a finger, a knuckle, a β-ball and a palm. We applied a systematic computational approach to identify putative pH sensor(s) of ASICIa. The role of putative pH sensors has been tested by site-directed mutagenesis and chemical modification combined with functional analysis in order to understand how changes in pH open these channels. The pH sensors are aspartic and glutamic acids distributed throughout the extracellular loop, suggesting that changes in pH control activation and inactivation of ASIC by protonation / deprotonation of many residues in different parts of the protein. During activation the protonation of various residues at the interface between the finger, the thumb and the β-ball induces the movement of the thumb toward the finger and the β-ball. During inactivation of the channel the palms of the three subunits forming a cavity approach each other. No histidine has been shown to be involved in extracellular pH changes detection, i.e. no histidine is a pH- sensor. Two histidines of ASIC2 bind Zn2+ and alter the apparent affinity of channel for protons. Only one of the two His is conserved among all ASICs, hASICIa H163. This residue is part of a network of hydrogen bonding with its conserved neighbors. The detailed study of this area, the interzone, shows its importance in the functional expression of ASICs. Disturbance of this network by the introduction of hydrophobic residues decreases the cell surface channel expression. Chemical modification of the introduced cysteines by thiol reactive compounds inhibits the mutated channels by a reduction of their open probability. These studies describe the effects of extracellular acidification on ASICs. RESUME GRAND PUBLIC: Etude de l'activation et de l'inactivation pH-dépendantes des canaux ASICs (Acid-Sensing Ion Channels) Benoîte BARGETON, Département de Pharmacologie et de Toxicologie, Université de Lausanne, rue du Bugnon 27, CH-1005 Lausanne, Suisse La transmission synaptique est un processus chimique entre deux neurones impliquant des neurotransmetteurs et leurs récepteurs. Un dysfonctionnement de certains types de synapses est à l'origine de beaucoup de troubles nerveux, tels que certaine forme d'épilepsie et de l'attention. Les récepteurs des neurotransmetteurs sont de très bonnes cibles thérapeutiques dans de nombreuses neuropathologies. Les canaux ASICs sont impliqués dans la neurodégénération consécutive à une attaque cérébrale et les bloquer pourraient permettre aux patients d'avoir moins de séquelles. Les canaux ASICs sont des détecteurs de l'acidité qui apparaît lors de situations pathologiques comme l'ischémie et l'inflammation. Ces canaux sont également impliqués dans des douleurs. Cibler spécifiquement ces canaux permettrait d'avoir de nouveaux outils thérapeutiques car à l'heure actuelle l'inhibiteur de choix, l'amiloride, bloque beaucoup d'autres canaux empêchant son utilisation pour bloquer les ASICs. C'est pourquoi il faut connaître et comprendre les bases moléculaires du fonctionnement de ces récepteurs. Les ASICs formés de trois sous-unités détectent les variations de l'acidité puis s'ouvrent transitoirement pour laisser entrer des ions chargés positivement dans la cellule ce qui active la signalisation neuronale. Afin de comprendre les bases moléculaires de l'activité des ASICs nous avons déterminé les sites de liaison des protons (pH-senseurs), ligands naturels des ASICs et décrit une zone importante pour l'expression fonctionnelle de ces canaux. Grâce à une validation systématique de résultats obtenus en collaboration avec l'Institut Suisse de Bioinformatique, nous avons décrit les pH-senseurs de ASICIa. Ces résultats, combinés à ceux d'autres groupes de recherche, nous ont permis de mieux comprendre comment les ASICs sont ouverts par une acidification du milieu extracellulaire. Une seconde étude souligne le rôle structural crucial d'une région conservée parmi tous les canaux ASICs : y toucher c'est diminuer l'activité de la protéine. Ce domaine permet l'harmonisation des changements dus à l'acidification du milieu extracellulaire au sein d'une même sous-unité c'est-à-dire qu'elle participe à l'induction de l'inactivation due à l'activation du canal Cette étude décrit donc quelle région de la protéine atteindre pour la bloquer efficacement en faisant une cible thérapeutique de choix.

A combined computational and functional approach identifies new residues involved in pH-dependent gating of ASIC1a.

Acid-sensing ion channels (ASICs) are key receptors for extracellular protons. These neuronal nonvoltage-gated Na(+) channels are involved in learning, the expression of fear, neurodegeneration after ischemia, and pain sensation. We have applied a systematic approach to identify potential pH sensors in ASIC1a and to elucidate the mechanisms by which pH variations govern ASIC gating. We first calculated the pK(a) value of all extracellular His, Glu, and Asp residues using a Poisson-Boltzmann continuum approach, based on the ASIC three-dimensional structure, to identify candidate pH-sensing residues. The role of these residues was then assessed by site-directed mutagenesis and chemical modification, combined with functional analysis. The localization of putative pH-sensing residues suggests that pH changes control ASIC gating by protonation/deprotonation of many residues per subunit in different channel domains. Analysis of the function of residues in the palm domain close to the central vertical axis of the channel allowed for prediction of conformational changes of this region during gating. Our study provides a basis for the intrinsic ASIC pH dependence and describes an approach that can also be applied to the investigation of the mechanisms of the pH dependence of other proteins.

Removal of Cadmium, Lead and Arsenic from Water by Lactic Acid Bacteria

A number of contaminants such as arsenic, cadmium and lead are released into the environment from natural and anthropogenic sources contaminating food and water. Chronic oral ingestion of arsenic, cadmium and lead is associated with adverse effects in the skin, internal organs and nervous system. In addition to conventional methods, biosorption using inactivated biomasses of algae, fungi and bacteria has been introduced as a novel method for decontamination of toxic metals from water. The aim of this work was to evaluate the applicability of lactic acid bacteria as tools for heavy metal removal from water and characterize their properties for further development of a biofilter. The results established that in addition to removal of mycotoxins, cyanotoxins and heterocyclic amines, lactic acid bacteria have a capacity to bind cationic heavy metals, cadmium and lead. The binding was found to be dependent on the bacterial strain and pH, and occurred rapidly on the bacterial surface, but was reduced in the presence of other cationic metals. The data demonstrates that the metals were bound by electrostatic interactions to cell wall components. Transmission electron micrographs showed the presence of lead deposits on the surface of biomass used in the lead binding studies, indicating involvement of another uptake/binding mechanism. The most efficient strains bound up to 55 mg Cd and 176 mg Pb / g dry biomass. A low removal of anionic As(V) was also observed after chemical modification of the cell wall. Full desorption of bound cadmium and lead using either dilute HNO₃ or EDTA established the reversibility of binding. Removal of both metals was significantly reduced when biomass regenerated with EDTA was used. Biomass regenerated with dilute HNO3 retained its cadmium binding capacity well, but lead binding was reduced. The results established that the cadmium and lead binding capacity of lactic acid bacteria, and factors affecting it, are similar to what has been previously observed for other biomasses used for the same purpose. However, lactic acid bacteria have a capacity to remove other aqueous contaminants such as cyanotoxins, which may give them an additional advantage over the other alternatives. Further studies focusing on immobilization of biomass and the removal of several contaminants simultaneously using immobilized bacteria are required.

Streptavidin - A Versatile Binding Protein for Solid-Phase Immunoassays

Streptavidin, a tetrameric protein secreted by Streptomyces avidinii, binds tightly to a small growth factor biotin. One of the numerous applications of this high-affinity system comprises the streptavidin-coated surfaces of bioanalytical assays which serve as universal binders for straightforward immobilization of any biotinylated molecule. Proteins can be immobilized with a lower risk of denaturation using streptavidin-biotin technology in contrast to direct passive adsorption. The purpose of this study was to characterize the properties and effects of streptavidin-coated binding surfaces on the performance of solid-phase immunoassays and to investigate the contributions of surface modifications. Various characterization tools and methods established in the study enabled the convenient monitoring and binding capacity determination of streptavidin-coated surfaces. The schematic modeling of the monolayer surface and the quantification of adsorbed streptavidin disclosed the possibilities and the limits of passive adsorption. The defined yield of 250 ng/cm² represented approximately 65 % coverage compared with a modelled complete monolayer, which is consistent with theoretical surface models. Modifications such as polymerization and chemical activation of streptavidin resulted in a close to 10-fold increase in the biotin-binding densities of the surface compared with the regular streptavidin coating. In addition, the stability of the surface against leaching was improved by chemical modification. The increased binding densities and capacities enabled wider high-end dynamic ranges in the solid-phase immunoassays, especially when using the fragments of the capture antibodies instead of intact antibodies for the binding of the antigen. The binding capacity of the streptavidin surface was not, by definition, predictive of the low-end performance of the immunoassays nor the assay sensitivity. Other features such as non-specific binding, variation and leaching turned out to be more relevant. The immunoassays that use a direct surface readout measurement of time-resolved fluorescence from a washed surface are dependent on the density of the labeled antibodies in a defined area on the surface. The binding surface was condensed into a spot by coating streptavidin in liquid droplets into special microtiter wells holding a small circular indentation at the bottom. The condensed binding area enabled a denser packing of the labeled antibodies on the surface. This resulted in a 5 - 6-fold increase in the signal-to-background ratios and an equivalent improvement in the detection limits of the solid-phase immunoassays. This work proved that the properties of the streptavidin-coated surfaces can be modified and that the defined properties of the streptavidin-based immunocapture surfaces contribute to the performance of heterogeneous immunoassays.

Eletrodeposição de irídio em tubo de grafite como modificador químico permanente em espectrometria de absorção atômica

A tubular electrochemical flow-cell for iridium deposition on the inner surface of pyrolytic graphite tube for permanent chemical modification is proposed. A transversal heated graphite tube was used as working electrode, a cylindrical piece of graphite inserted into the graphite tube as auxiliary electrode, and a micro Ag/AgCl(sat) as reference electrode. Iridium solution in 1.0 mol L-1 HCl, flowing at 0.55 mL min-1 for 60 min was used to perform the electrochemical modification. The applied potential to the flow-cell was - 0.700 V vs Ag/AgCl. Scanning electron microscopy images were taken for thermal and electrochemical modified graphite surface in order to evaluate the iridium distribution. Selenium hydride trapping was used to verify the performance of the proposed permanent chemical modifier.

Funcionalização de nanotubos de Carbono

Carbon nanotubes are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Many applications of carbon nanotubes require their chemical modification in order to tune/control their physico-chemical properties. One way of achieving this control is carrying out functionalization processes where atoms and molecules interact (covalent or non-covalent) with the nanotubes. We review some of the progress that has been made in chemical functionalization of carbon nanotubes. Emphasis is given to chemical strategies, the most used techniques, and applications.

Determination of Cd and Pb in fuel ethanol by filter furnace electrothermal atomic absorption spectrometry

A method was developed for quantification of Cd and Pb in ethanol fuel by filter furnace atomic absorption spectrometry. Filter furnace was used to eliminate the need for chemical modification, to stabilize volatile analytes and to allow the application of short pyrolysis step. The determinations in samples were carried out against calibration solutions prepared in ethanol. Recovery tests were made in seven commercial ethanol fuel samples with values between 90 and 120%. Limits of detection were 0.1 µg L-1 for Cd and 0.3 µg L-1 for Pb. Certified water samples (APS 1071, APS 1033, NIST 1643d, NIST 1640) were also used to evaluate accuracy and recoveries from 86.8% to115% were obtained.

Modificação química de argilas: desafios científicos e tecnológicos para obtenção de novos produtos com maior valor agregado

Chemical modification of clays is possible due to their ion-exchange and adsorption capacities, which allows the adjustment of the physicochemical properties of the surfaces of their layers. This modification makes possible the use of clays to produce a great number of new materials, which range from coarse applications such as oil based drilling fluids to refined applications such as pharmaceutical products. This article intends to expose where there is still space for research and investment aiming at the performance improvement of clay-based materials.

Poliuretanos elastoméricos obtenidos a partir de aceite de ricino y almidón de yuca original y modificado con anhídrido propiónico: síntesis, propiedades fisicoquímicas y fisicomecánicas

Chemical modification of cassava starch was conducted through an acylation reaction by using pyridine and propionic anhydride to replace the functional groups of starch. Polyurethane elastomers were prepared using suspensions of the mixture obtained from castor oil and yucca starch that was modified by a propionic anhydride reaction. The suspensions were characterized by means of tests based on The Fourier Transform Infrared Spectroscopy and the Hydroxyl Index. The castor oil-AMP suspensions were used for the PU synthesis. The PUs were characterized by their physical-mechanical properties like tension- deformation and Shore A. hardness, thermal gravimetric analysis and swelling test. The density cross-linking of from swelling tests was determined by applying the Flory-Rehner equation.

Os nanomateriais e a descoberta de novos mundos na bancada do químico

In recent years there has been great progress in the field of nanotechnology largely driven by research into nanomaterials. Chemistry appears in this context for its relevant role in the synthesis and surface modification of nanomaterials. This review article discusses fundamental concepts related to the synthesis and properties of inorganic nanoparticles with diverse properties. Aspects related to unique size dependent optical and magnetic properties are discussed and the chemistry involved in the preparation of nanomaterials reviewed. Fundamental aspects of the chemical modification of nanoparticles envisaging potential applications for these materials are also addressed.

CARACTERIZAÇÃO E AVALIAÇÃO IN VITRO DE NANOCOMPÓSITOS DE POLI (L-ÁCIDO LÁTICO) E NANOTUBOS DE CARBONO DE PAREDES MÚLTIPLAS PURIFICADOS

Carbon nanotubes (CNT) have been studied for biomedical applications due to their unique properties. However, pristine CNT have structural features and impurities that can cause toxicity to biological systems. In this work, we describe a method to purify multiwalled carbon nanotubes (MWCNT) by chemical modification and subsequent attachment of hydroxyl and carboxyl groups to improve dispersion and to decrease toxic effects. Nanocomposites from poly (L-lactic acid) (PLLA) and nanotubes were produced by the solvent casting method and characterized and evaluated for cytocompatibility with Vero cells. The nanocomposite interactions with Vero cells demonstrated that the cells were able to adhere and sustain proliferation and showed favorable cytocompatibility. In vitro studies also revealed an increase in fibroblast cell viability in the nanocomposites, compared with neat PLLA.

Hemiselluloosien erotus ja in situ -modifiointi

Hemiselluloosat kuuluvat selluloosan ja ligniinin ohella puun ja muiden kasvimateriaalien päärakenneaineksiin. Hemiselluloosan kemiallisessa koostumuksessa on eroja kasvilajien välillä, mikä tekee ryhmästä hyvin monimuotoisen. Lehtipuiden pääasiallinen hemiselluloosa on glukuroniksylaani. Ksylaaneja esiintyy laajasti myös muissa kasveissa erilaisina rakenteina. Havupuiden yleisin hemiselluloosa on puolestaan galaktoglukomannaani. Arabinogalaktaani on erityisesti lehtikuusesta runsaana löytyvä hemiselluloosa, jota muissa puulajeissa on vain vähän. Luonnon polymeerejä tutkitaan jatkuvasti muun muassa vaihtoehtojen löytämiseksi raakaöljypohjaisille tuotteille. Aiemmin hemiselluloosia on pääosin hyödynnetty sellaisenaan tai jalostettu esimerkiksi sokereiksi. Selluloosan ja tärkkelyksen tavoin ne voivat kuitenkin toimia myös kemiallisen, fysikaalisen tai entsymaattisen muokkauksen lähtöaineena. Hemiselluloosien käyttöä rajoittaa usein se, että niiden eristäminen kasvimateriaalista hyvällä saannolla on vaikeaa. Useimmiten hemiselluloosa erotetaan biomassasta ligniinin poiston jälkeen uuttamalla erilaisilla reagensseilla, kuten emäksillä. Arabinogalaktaanin erottamiseen ei kuitenkaan vaadita ankaria olosuhteita, vaan yleisimmin siihen riittää uutto vedellä. Kalvosuodatus puolestaan on hyvä keino hemiselluloosan talteenottoon uuttoliuoksista. Tässä työssä tarkasteltiin arabinogalaktaanin erotusta siperianlehtikuusesta uuttokokein. Saadut uuttoliuokset konsentrointiin ja puhdistettiin kalvosuodatusmenetelmillä. Lisäksi tutkittiin eristetyn arabinogalaktaanin käyttöä kemiallisen muokkauksen lähtöaineena, missä pyrkimyksenä oli etenkin in situ -modifiointi suoraan uuttoliuoksessa oleville yhdisteille. Uuttokokeilla saatiin kuitenkin vain pieni osa lehtikuusen arabinogalaktaanista erotetuksi. Myös kalvosuodatusvaiheen aikana menetettiin osa uuttoliuosten arabinogalaktaanista. Koska arabinogalaktaanipitoisuus uuttoliuoksissa jäi hyvin alhaiseksi, in situ -modifiointeja oli vaikea saada onnistumaan. Uutto-olosuhteiden lisätutkimuksella sekä kiinnittämällä erityistä huomiota suodatuskalvojen valintaan voitaneen pitoisuutta nostaa ja saada lisämateriaalia kemiallista muokkausta varten.

Determination of Copper, Iron, Nickel and Zinc in fuel kerosene by FAAS after adsorption and pre-concentration on 2-aminothiazole-modified silica gel

Silica gel chemically modified with 2-Aminotiazole groups, abbreviated as SiAT, was used for preconcentration of copper, zinc, nickel and iron from kerosene, normally used as a engine fuel for airplanes. Surface characteristics and surface area of the silica gel were obtained before and after chemical modification using FT-IR, Kjeldhal and surface area analysis (B.E.T.). The retention and recovery of the analyte elements were studied by applying batch and column techniques. The experimental parameters, such as shaking time in batch technique, flow rate and concentration of the eluent (HCl- 0.25-2.00 mol L-1) and the amount of silica, on retention and elution, have been investigated. Detection limits of the method for copper, iron, nickel and zinc are 0.77, 2.92, 1.73 and 0.097 mg L-1, respectively. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in kerosene using flame AAS for their quantification.

Adsorption of hydrogen sulfide by modified cellulose nano/microcrystals

Hydrogen sulfide is toxic and hazardous pollutant. It has been under great interest for past few years because of all the time tighten environmental regulations and increased interest of mining. Hydrogen sulfide gas originates from mining and wastewater treatment systems have caused death in two cases. It also causes acid rains and corrosion for wastewater pipelines. The aim of this master thesis was to study if chemically modified cellulose nanocrystals could be used as adsorbents to purify hydrogen sulfide out from water and what are the adsorption capacities of these adsorbents. The effects of pH and backgrounds on adsorption capacities of different adsorbents are tested. In theoretical section hydrogen sulfide, its properties and different purification methods are presented. Also analytical detection methods for hydrogen sulfide are presented. Cellulose nano/microcrystals, properties, application and different modification methods are discussed and finally theory of adsorption and modeling of adsorption is shortly discussed. In experimental section different cellulose nanocrystals based adsorbents are prepared and tested at different hydrogen sulfide concentrations and in different conditions. Result of experimental section was that the highest adsorption capacity at one component adsorption had wet MFC/CaCO3. At different pH the adsorption capacities of adsorbents changed quite dramatically. Also change of hydrogen sulfide solution background did have effect on adsorption capacities. Although, when tested adsorbents’ adsorption capacities are compared to those find in literatures, it seems that more development of MFC based adsorbents is needed.

Cellular responses to stress and kinase signaling activation : apoptosis and differentiation

Stressignaler avkänns många gånger av membranbundna proteiner som översätter signalerna till kemisk modifiering av molekyler, ofta proteinkinaser Dessa kinaser överför de avkodade budskapen till specifika transkriptionsfaktorer genom en kaskad av sekventiella fosforyleringshändelser, transkriptionsfaktorerna aktiverar i sin tur de gener som behövs för att reagera på stressen. En av de mest kända måltavlorna för stressignaler är transkriptionsfaktor AP-1 familjemedlemen c-Jun. I denna studie har jag identifierat den nukleolära proteinet AATF som en ny regulator av c-Jun-medierad transkriptionsaktivitet. Jag visar att stresstimuli inducerar omlokalisering av AATF vilket i sin tur leder till aktivering av c-Jun. Den AATF-medierad ökningen av c-Jun-aktiviteten leder till en betydande ökning av programmerad celldöd. Parallellt har jag vidarekarakteriserat Cdk5/p35 signaleringskomplexet som tidigare har identifierats i vårt laboratorium som en viktig faktor för myoblastdifferentiering. Jag identifierade den atypiska PKCξ som en uppströms regulator av Cdk5/p35-komplexet och visar att klyvning och aktivering av Cdk5 regulatorn p35 är av fysiologisk betydelse för differentieringsprocessen och beroende av PKCξ aktivitet. Jag visar att vid induktion av differentiering fosforylerar PKCξ p35 vilket leder till calpain-medierad klyvning av p35 och därmed ökning av Cdk5-aktiviteten. Denna avhandling ökar förståelsen för de regulatoriska mekanismer som styr c-Jun-transkriptionsaktiviteten och c-Jun beroende apoptos genom att identifiera AATF som en viktig faktor. Dessutom ger detta arbete nya insikter om funktionen av Cdk5/p35-komplexet under myoblastdifferentiering och identifierar PKCξ som en uppströms regulator av Cdk5 aktivitet och myoblast differentiering.