YB-1 promotes microtubule assembly in vitro through interaction with tubulin and microtubules

<p>Abstract</p> <p>Background</p> <p>YB-1 is a major regulator of gene expression in eukaryotic cells. In addition to its role in transcription, YB-1 plays a key role in translation and stabilization of mRNAs.</p> <p>Results</p> <p>We show here that YB-1 interacts with tubulin and microtubules and stimulates microtubule assembly <it>in vitro</it>. High resolution imaging via electron and atomic force microscopy revealed that microtubules assembled in the presence of YB-1 exhibited a normal single wall ultrastructure and indicated that YB-1 most probably coats the outer microtubule wall. Furthermore, we found that YB-1 also promotes the assembly of MAPs-tubulin and subtilisin-treated tubulin. Finally, we demonstrated that tubulin interferes with RNA:YB-1 complexes.</p> <p>Conclusion</p> <p>These results suggest that YB-1 may regulate microtubule assembly <it>in vivo </it>and that its interaction with tubulin may contribute to the control of mRNA translation.</p

Fluorescence and spin properties of defects in single digit nanodiamonds

International audienceThis article reports stable photoluminescence and high-contrast optically detected electron spin resonance (ODESR) from single nitrogen-vacancy (NV) defect centers created within ultrasmall, disperse nanodiamonds of radius less than 4 nm. Unexpectedly, the efficiency for the production of NV fluorescent defects by electron irradiation is found to be independent of the size of the nanocrystals. Fluorescence lifetime imaging shows lifetimes with a mean value of around 17 ns, only slightly longer than the bulk value of the defects. After proper surface cleaning, the dephasing times of the electron spin resonance in the nanocrystals approach values of some microseconds, which is typical for the type Ib diamond from which the nanoparticle is made. We conclude that despite the tiny size of these nanodiamonds the photoactive nitrogen-vacancy color centers retain their bulk properties to the benefit of numerous exciting potential applications in photonics, biomedical labeling, and imaging

Polyamine Sharing between Tubulin Dimers Favours Microtubule Nucleation and Elongation via Facilitated Diffusion

We suggest for the first time that the action of multivalent cations on microtubule dynamics can result from facilitated diffusion of GTP-tubulin to the microtubule ends. Facilitated diffusion can promote microtubule assembly, because, upon encountering a growing nucleus or the microtubule wall, random GTP-tubulin sliding on their surfaces will increase the probability of association to the target sites (nucleation sites or MT ends). This is an original explanation for understanding the apparent discrepancy between the high rate of microtubule elongation and the low rate of tubulin association at the microtubule ends in the viscous cytoplasm. The mechanism of facilitated diffusion requires an attraction force between two tubulins, which can result from the sharing of multivalent counterions. Natural polyamines (putrescine, spermidine, and spermine) are present in all living cells and are potent agents to trigger tubulin self-attraction. By using an analytical model, we analyze the implication of facilitated diffusion mediated by polyamines on nucleation and elongation of microtubules. In vitro experiments using pure tubulin indicate that the promotion of microtubule assembly by polyamines is typical of facilitated diffusion. The results presented here show that polyamines can be of particular importance for the regulation of the microtubule network in vivo and provide the basis for further investigations into the effects of facilitated diffusion on cytoskeleton dynamics

Procédé de marquage d'un objet par microdiamants

L'invention concerne un procédé de marquage d'un objet. Ce procédé comporte les étapes suivantes : (a) On fournit plusieurs microdiamants (10) fluorescents dont la dimension maximale de chacun est inférieure à 50 microns, (b) On répartit ces microdiamants (10) dans une région (95) de cet objet (90) à des positions, (c) On fixe ces microdiamants dans cette région (95)

Rapid Assembly and Collective Behavior of Microtubule Bundles in the Presence of Polyamines

International audienceMicrotubules (MTs) are cylindrical cytoskeleton polymers composed of α-β tubulin heterodimers whose dynamic properties are essential to fulfill their numerous cellular functions. In response to spatial confinement, dynamic MTs, even in the absence of protein partners, were shown to self-organize into higher order structures (spindle or striped structures) which lead to interesting dynamical properties (MT oscillations). In this study, we considered the assembly and sensitivity of dynamic MTs when in bundles. To perform this study, spermine, a natural tetravalent polyamine present at high concentrations in all eukaryote cells, was used to trigger MT bundling while preserving MT dynamics. Interestingly, we first show that, near physiological ionic strengths, spermine promotes the bundling of MTs whereas it does not lead to aggregation of free tubulin, which would have been detrimental to MT polymerization. Experimental and theoretical results also indicate that, to obtain a high rate of bundle assembly, bundling should take place at the beginning of assembly when rapid rotational movements of short and newly nucleated MTs are still possible. On the other hand, the bundling process is significantly slowed down for long MTs. Finally, we found that short MT bundles exhibit a higher sensitivity to cold exposure than do isolated MTs. To account for this phenomenon, we suggest that a collective behavior takes place within MT bundles because an MT entering into a phase of shortening could increase the probability of the other MTs in the same bundle to enter into shortening phase due to their close proximity. We then elaborate on some putative applications of our findings to in vivo conditions including neurons

Cellule photovoltaique avec diamants fluorescents

L'invention concerne une cellule photovoltaïque (1) comportant une première couche (10) qui est apte à générer une tension électrique lorsqu'elle est illuminée et qui est à base d'un matériau dont le spectre de sensibilité lumineuse est maximum entre 600 nm et 1300 nm. Cette cellule photovoltaïque (1) comporte sur la première couche (10) une seconde couche (20) comprenant des diamants fluorescents (30), cette seconde couche (20) étant une couche du côté extérieur de la cellule photovoltaïque (1) de telle sorte que des rayons lumineux sont aptes à illuminer ces diamants fluorescents (30)

Catalysis and specificity of the polycondensation of aminopropyltrimethoxysilane on nucleic acids

International audienceThe polycondensation of a silane derivative such as aminopropyltrimethoxysilane (ATMS) in the presence of nucleic acids has never been investigated. Our group has previously demonstrated that in chloroform ATMS hydrolysis and polycondensation were faster when the reaction were carried out in the presence of double stranded DNA (146 bp). The results showed that the kinetics of ATMS hydrolysis was affected by the base type used, a fast hydrolysis reaction rate being observed with nucleotide molecules containing adenosine group, and that in the absence of water the amino group of deoxyadenosine units, and not the hydroxylic group of the sucrose residue, can react with ATMS methoxy groups. The present work was initiated aiming at providing a better understanding of this effect. It was observed that the polymerization degree of oligodeoxyadenylate has a clear impact on the kinetic of reaction this effect being as much important as the polymerization degree of the oligodeoxyadenylate was high. Structural investigation by molecular modeling showed that this enhanced reactivity can be explained by conformational effects. Altogether, these results are accounted for assuming that DNA can act as a specific template for ATMS polycondensation, in organic medium such as chloroform, opening the way to possible DNA encapsulation, and a new way for DNA chemical modification in organic solvent

A synergistic relationship between three regions of stathmin family proteins is required for the formation of a stable complex with tubulin.

Stathmin is a ubiquitous 17 kDa cytosolic phosphoprotein proposed to play a general role in the integration and relay of intracellular signalling pathways. It is believed to regulate microtubule dynamics by sequestering tubulin in a complex made of two tubulin heterodimers per stathmin molecule (T2S complex). The other proteins of the stathmin family can also bind two tubulin heterodimers through their SLD (stathmin-like domain), but the different tubulin:SLD complexes display varying stabilities. In this study, we analysed the relative influence of three regions of SLDs on the interaction with tubulin and the mechanistic processes that lead to its sequestration. Tubulin-binding properties of fragments and chimaeras of stathmin and RB3(SLD) were studied in vitro by tubulin polymerization, size-exclusion chromatography and surface plasmon resonance assays. Our results show that the N-terminal region of SLDs favours the binding of the first tubulin heterodimer and that the second C-terminal tubulinbinding site confers the specific stability of a given tubulin:SLD complex. Our results highlight the molecular processes by which tubulin co-operatively interacts with the SLDs. This knowledge may contribute to drug development aimed at disturbing microtubules that could be used for the treatment of cancer