Dynéine | EPFL Graph Search

thumb|Complexe de dynéine. Les dynéines sont des complexes protéiques d’environ 2 MDa, comportant deux ou trois chaînes lourdes, deux chaînes intermédiaires et huit chaînes légères. Elles sont associées à des microtubules, se dirigeant vers leur extrémité « - » (centripètes), et possèdent plusieurs rôles différents. Les dynéines ne fonctionnent qu'avec un complexe protéique associé, la dynactine. Activités des dynéines On distingue :

les dynéines axonémalesElles sont fixées à l'un des microtubules des doublets présents en périphérie d'un axonème. Par une activité ATPasique, elles font glisser les tubules entre eux, provoquant leur courbure. Tous les tubules glissant simultanément, les cils et les flagelles sont ainsi mis en mouvement.
les dynéines cytoplasmiquesElles sont fixées sur les microtubules du cytoplasme. Par une activité ATPasique, elles permettent les déplacements de vésicules qui leur sont associées, vers le centre de la cellule, c’est-à-dire vers l'

Mechanisms of centrosome separation in C. elegans

Alessandro De Simone

Centrosomes are the major microtubule organizing centers of animal cells. The two centrosomes present at the onset of mitosis must separate in a timely fashion along the nuclear envelope to ensure proper bipolar spindle assembly and thus genome stability. Microtubuleassociated motors of the kinesin-5 family are required for centrosome separation in several systems, but are partially redundant or entirely dispensable in others, where the minus-end directed motor dynein plays an important role. The mechanisms by which dynein powers centrosome separation are incompletely understood. Furthermore, the nature of the symmetry-breaking mechanisms that imbalance the forces acting on centrosomes to favor theirmovement away from each other are not known. We addressed these questions using a combination of 3D time-lapse microscopy, image processing and computational modeling to dissect centrosome separation in the polarized one-cell C. elegans embryo that entirely relies on dynein for this process. First, we have characterized the quantitative features of centrosome separation in the wild-type. Next, we compared centrosome separation between wild-type and mutant/RNAi conditions. Our analysis revealed that centrosome separation is powered by the combined action of dynein at the nuclear envelope and at the cell cortex. Moreover, we demonstrated that cortical dynein requires actomyosin contractility to separate centrosomes. These observations suggest that cortical dynein acts by harnessing anterior-directed actomyosin cortical flows initiated earlier in the cell cycle by the centrosomes themselves. To confirmthismodel, we successfully tested experimentally two of its key predictions, namely that dynein complexes flow toward the anterior together with the cortex and that the velocity of centrosome separation correlates with that of the flow of the nearby cortex. Taken together, these results demonstrate that centrosome separation is driven by nuclear and cortical dynein, where the latter acts by transmitting forces produced by the cortical actomyosin flow. To test whether this model is sufficient to explain centrosome separation, we developed a 3D computationalmodel of cytoskeleton dynamics. Indeed, predicted centrosome separation agrees quantitatively with the experimental observations in wild-type and mutant/RNAi conditions. Moreover, the qualitative predictions of the model are robust for parameter changes. Furthermore, computational simulations demonstrate that forces are intrinsically organized to move centrosomes away from each other without the need of any extrinsic symmetry-breaking mechanism. Indeed, in the case of nuclear dynein-driven separation, the position of centrosomes between the nuclear envelope and the cortex results in an asymmetric microtubule aster that leads to centrosome outward movement. In the case of cortical dynein, cortical flows are triggered by centrosomes and always move away from them, such that their forces are always directed to separate centrosomes. Therefore, this separation mechanism functions irrespective of the initial position of centrosomes along the cortex. In conclusion, in this thesis we uncover a novel organizing principle in which dynein, coupled with cell geometry and flow pattern, serves to robustly separate centrosomes and thus ensure genome stability.

EPFL2016

Dynein Transmits Polarized Actomyosin Cortical Flows to Promote Centrosome Separation

Alessandro De Simone, Pierre Gönczy

The two centrosomes present at the onset of mitosis must separate in a timely and accurate fashion to ensure proper bipolar spindle assembly. The minus-end-directed motor dynein plays a pivotal role in centrosome separation, but the underlying mechanisms remain elusive, particularly regarding how dynein coordinates this process in space and time. We addressed these questions in the one-cell C. elegans embryo, using a combination of 3D timelapse microscopy and computational modeling. Our analysis reveals that centrosome separation is powered by the joint action of dynein at the nuclear envelope and at the cell cortex. Strikingly, we demonstrate that dynein at the cell cortex acts as a force-transmitting device that harnesses polarized actomyosin cortical flows initiated by the centrosomes earlier in the cell cycle. This mechanism elegantly couples cell polarization with centrosome separation, thus ensuring faithful cell division.

Elsevier2016

Computer simulations reveal mechanisms that organize nuclear dynein forces to separate centrosomes

Alessandro De Simone, Pierre Gönczy

Centrosome separation along the surface of the nucleus at the onset of mitosis is critical for bipolar spindle assembly. Dynein anchored on the nuclear envelope is known to be important for centrosome separation, but it is unclear how nuclear dynein forces are organized in an anisotropic manner to promote the movement of centrosomes away from each other. Here we use computational simulations of Caenorhabditis elegans embryos to address this fundamental question, testing three potential mechanisms by which nuclear dynein may act. First, our analysis shows that expansion of the nuclear volume per se does not generate nuclear dynein-driven separation forces. Second, we find that steric interactions between microtubules and centrosomes contribute to robust onset of nuclear dynein-mediated centrosome separation. Third, we find that the initial position of centrosomes, between the male pronucleus and cell cortex at the embryo posterior, is a key determinant in organizing microtubule aster asymmetry to power nuclear dynein-dependent separation. Overall our work reveals that accurate initial centrosome position, together with steric interactions, ensures proper anisotropic organization of nuclear dynein forces to separate centrosomes, thus ensuring robust bipolar spindle assembly.

Amer Soc Cell Biology2017

Mechanisms of centrosome separation in C. elegans

Alessandro De Simone

EPFL2016