Fission yeast spindle dynamics and chromosome segregation fidelity show distinct thermosensitivity.

Cellular processes rely on proteins with temperature-dependent stability and activity. While thermosensitivity in biological networks is well-explored, the effect of temperature on complex mechanochemical assemblies, like the spindle, is rarely studied. We examined fission yeast spindle dynamics and chromosome segregation from 15⁰C to 40⁰C.

Prolongation of mitosis is associated with enhanced endogenous DNA damage in fission yeast.

Mitosis is usually shorter than other phases of the cell cycle and maintains a consistent duration despite variations in cell size and spindle size. This suggests the existence of a compensatory mechanism that ensures a short duration, possibly as a protective measure against irreversible damage, such as DNA damage. To explore the link between prolonged mitosis and DNA damage, we develop a microscopy-based assay utilizing Rad52-GFP as a marker for mitotic DNA damage.

Reliable and robust control of nucleus centering is contingent on nonequilibrium force patterns.

Cell centers their division apparatus to ensure symmetric cell division, a challenging task when the governing dynamics is stochastic. Using fission yeast, we show that the patterning of nonequilibrium polymerization forces of microtubule (MT) bundles the precise localization of spindle pole body (SPB), and hence the division septum, at the onset of mitosis. We define two cellular objectives, , the mean SPB position relative to the geometric center, and , the variance of the SPB position, which are sensitive to genetic perturbations that change cell length, MT bundle number/orientation, and MT dynamics.

Multiple Motifs Compete for EB-Dependent Microtubule Plus End Binding.

Microtubule (MT) dynamics are regulated by a plethora of microtubule-associated proteins (MAPs). An important MT regulator is the end binding protein EB, which serves as a scaffold to recruit other MAPs to MT plus ends. In this issue of Structure, Kumar et al.

Binding of DNA-bending non-histone proteins destabilizes regular 30-nm chromatin structure.

Why most of the in vivo experiments do not find the 30-nm chromatin fiber, well studied in vitro, is a puzzle. Two basic physical inputs that are crucial for understanding the structure of the 30-nm fiber are the stiffness of the linker DNA and the relative orientations of the DNA entering/exiting nucleosomes. Based on these inputs we simulate chromatin structure and show that the presence of non-histone proteins, which bind and locally bend linker DNA, destroys any regular higher order structures (e.

Statistical mechanics provides novel insights into microtubule stability and mechanism of shrinkage.

Microtubules are nano-machines that grow and shrink stochastically, making use of the coupling between chemical kinetics and mechanics of its constituent protofilaments (PFs). We investigate the stability and shrinkage of microtubules taking into account inter-protofilament interactions and bending interactions of intrinsically curved PFs. Computing the free energy as a function of PF tip position, we show that the competition between curvature energy, inter-PF interaction energy and entropy leads to a rich landscape with a series of minima that repeat over a length-scale determined by the intrinsic curvature.

Forces due to curving protofilaments in microtubules.

Microtubules consist of 13 protofilaments arranged in the form of a cylinder. The protofilaments are composed of longitudinally attached tubulin dimers that can exist in either a less curved state [GTP-bound tubulin (T)] or a more curved state [GDP-bound tubulin (D)]. Hydrolysis of T into D leaves the straight and laterally attached protofilaments of the microtubule in a mechanically stressed state, thus leading to their unzipping.

History-dependent depolymerization of actin filaments.

Depolymerizing cytoskeletal filaments are involved in cell division, cell motility, and other cellular functions. Understanding the dynamics of depolymerization is as important as understanding the dynamics of polymerization. We study nonequilibrium depolymerization of actin filaments using a simple two-state model.