reconstitution-basic-mitotic-spindles-spherical-emulsion

Reconstitution of Basic Mitotic Spindles in Spherical Emulsion Droplets

Mitotic spindle assembly, positioning and orientation depend on the combined forces generated by microtubule dynamics, microtubule motor proteins and ...

Delft University of Technology

The natural history of paroxysmal nocturnal hemoglobinuria (PNH) clinical subcategories (classic PNH and aplastic anemia [AA]/PNH syndrome) is still unknown. We retrospectively studied 460 PNH patients diagnosed in 58 French hematologic centers from 1950 to 2005. The median (SE) follow-up time was 6.8 (0.5) years. The median survival time (SE) was 22 (2.5) years. We identified 113 patients with classic PNH, 224 patients with AA-PNH syndrome, and 93 (22%) intermediate patients who did not fit within these 2 categories. At presentation, classic PNH patients were older, with more frequent abdominal pain and displayed higher levels of GPI-AP-deficient granulocytes. A time-dependent improved survival was observed. In classic PNH, diagnoses before 1986 (hazard ratio [HR]: 3.6; P = .01) and increasing age (P < .001) were associated with worse survival prognoses, whereas use of androgens within the first year after diagnosis was protective (HR, 0.17; P = .01). Transfusions before 1996 (HR, 2.7; P = .007) led to lower survival rates in patients with AA-PNH syndrome, whereas immunosuppressive treatment was associated with better outcomes (HR, 0.33; P = .03). Evolution to thrombosis affected survival in both subcategories (classic PNH: HR, 7.8 [P < .001]; AA-PNH syndrome: HR, 33.0 [P < .001]). Evolution to bicytopenia or pancytopenia for classic PNH (HR, 7.3, P < .001) and malignancies for AA-PNH syndrome (HR, 48.8; P < .001) were associated with worse outcomes. Although clinical presentation and prognosis factors are different, classic PNH and AA-PNH syndrome present roughly similar outcomes, affected mainly by complications.

Paroxysmal nocturnal hemoglobinuria: natural history of disease subcategories.

An approach is developped to gain control over the polarity of neuronal networks at the cellular level by physically constraining cell development by the use of micropatterns. It is demonstrated that the position and path of individual axons, the cell extension that propagates the neuron output signal, can be chosen with a success rate higher than 85%. This allows the design of small living computational blocks above silicon nanowires.

Neuronal architectures with axo-dendritic polarity above silicon nanowires.

Neuronal differentiation is under the tight control of both biochemical and physical information arising from neighboring cells and micro-environment. Here we wished to assay how external geometrical constraints applied to the cell body and/or the neurites of hippocampal neurons may modulate axonal polarization in vitro. Through the use of a panel of non-specific poly-L-lysine micropatterns, we manipulated the neuronal shape. By applying geometrical constraints on the cell body we provided evidence that centrosome location was not predictive of axonal polarization but rather follows axonal fate. When the geometrical constraints were applied to the neurites trajectories we demonstrated that axonal specification was inhibited by curved lines. Altogether these results indicated that intrinsic mechanical tensions occur during neuritic growth and that maximal tension was developed by the axon and expressed on straight trajectories. The strong inhibitory effect of curved lines on axon specification was further demonstrated by their ability to prevent formation of multiple axons normally induced by cytochalasin or taxol treatments. Finally we provided evidence that microtubules were involved in the tension-mediated axonal polarization, acting as curvature sensors during neuronal differentiation. Thus, biomechanics coupled to physical constraints might be the first level of regulation during neuronal development, primary to biochemical and guidance regulations.

How morphological constraints affect axonal polarity in mouse neurons.

During important cellular processes such as centrosome and spindle positioning, dynein at the cortex interacts with dynamic microtubules in an apparent "end-on" fashion. It is well-established that dynein can generate forces by moving laterally along the microtubule lattice, but much less is known about dynein's interaction with dynamic microtubule ends. In this paper, we review recent in vitro experiments that show that dynein, attached to an artificial cortex, is able to capture microtubule ends, regulate microtubule dynamics and mediate the generation of pulling forces on shrinking microtubules. We further review existing ideas on the involvement of dynein-mediated cortical pulling forces in the positioning of microtubule organizing centers such as centrosomes. Recent in vitro experiments have demonstrated that cortical pulling forces in combination with pushing forces can lead to reliable centering of microtubule asters in quasi two-dimensional microfabricated chambers. In these experiments, pushing leads to slipping of microtubule ends along the chamber boundaries, resulting in an anisotropic distribution of cortical microtubule contacts that favors centering, once pulling force generators become engaged. This effect is predicted to be strongly geometry-dependent, and we therefore finally discuss ongoing efforts to repeat these experiments in three-dimensional, spherical and deformable geometries.

End-on microtubule-dynein interactions and pulling-based positioning of microtubule organizing centers.

Cytoplasmic dynein is a major microtubule (MT)-associated motor in nearly all eukaryotic cells. A subpopulation of dyneins associates with the cell cortex and the interaction of this cortical dynein with MTs helps to drive processes such as nuclear migration, mitotic spindle orientation, and cytoskeletal reorientation during wound healing. In this chapter, we describe three types of assays in which interactions between cortical dynein and MTs are reconstituted in vitro at increasing levels of complexity. In the first 1D assay, MTs, nucleated from a centrosome attached to a surface, grow against dynein-coated gold barriers. In this assay configuration, the interactions between MTs and dynein attached to a barrier can be studied in great detail. In the second and third assays, a freely moving dynamic aster is placed in either a 2D microfabricated chamber or a 3D water-in-oil emulsion droplet, with dynein-coated boundaries. These assays can be used to study how cortical dynein positions centrosomes. Finally, we discuss future possibilities for increasing the complexity of these reconstituted systems.

Reconstitution of cortical Dynein function.

Establishment of cell polarity is essential for processes such as growth and division. In fission yeast, as well as other species, polarity factors travel at the ends of microtubules to cortical sites where they associate with the membrane and subsequently maintain a polarized activity pattern despite their ability to diffuse in the membrane. In this chapter we present methods to establish an in vitro system that captures the essential features of this process. This bottom-up approach allows us to identify the minimal molecular requirements for microtubule-based cell polarity. We employ microfabrication techniques combined with surface functionalization to create rigid chambers with affinity for proteins, as well as microfluidic techniques to create and shape emulsion droplets with functionalized lipid boundaries. Preliminary results are shown demonstrating that a properly organized microtubule cytoskeleton can be confined to these confined spaces, and proteins traveling at the ends of growing microtubules can be delivered to their boundaries.

In vitro systems for the study of microtubule-based cell polarity in fission yeast.

The kinesin-3 motor KIF1A is in charge of vesicular transport in neuronal axons. Its single-headed form is known to be very inefficient due to the presence of a diffusive state in the mechanochemical cycle. However, recent theoretical studies have suggested that these motors could largely enhance force generation by working in teams. Here we test this prediction by challenging single-headed KIF1A to extract membrane tubes from giant vesicles along microtubule filaments in a minimal in vitro system. Remarkably, not only KIF1A motors are able to extract tubes but they feature a novel phenomenon: tubes are wound around microtubules forming tubular helices. This finding reveals an unforeseen combination of cooperative force generation and self-organized manoeuvreing capability, suggesting that the diffusive state may be a key ingredient for collective motor performance under demanding traffic conditions. Hence, we conclude that KIF1A is a genuinely cooperative motor, possibly explaining its specificity to axonal trafficking.

Article	Year
Paroxysmal nocturnal hemoglobinuria: natural history of disease subcategories. Blood\| PubMed ID: 18535202	2008
Neuronal architectures with axo-dendritic polarity above silicon nanowires. Small (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 22228548	2012
How morphological constraints affect axonal polarity in mouse neurons. PloS one\| PubMed ID: 22457779	2012
End-on microtubule-dynein interactions and pulling-based positioning of microtubule organizing centers. Cell cycle (Georgetown, Tex.)\| PubMed ID: 22895049	2012
Reconstitution of cortical Dynein function. Methods in enzymology\| PubMed ID: 24630109	2014
In vitro systems for the study of microtubule-based cell polarity in fission yeast. Methods in cell biology\| PubMed ID: 25997339	2015
Formation of helical membrane tubes around microtubules by single-headed kinesin KIF1A. Nature communications\| PubMed ID: 26268542	2015

Sophie Roth

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