Abstract
SummaryEukaryotic cells position the nucleus within the proper intracellular space, thereby safeguarding a variety of cellular processes. In fission yeast, the interphase nucleus is placed in the cell middle in a microtubule-dependent manner. By contrast, how the mitotic nucleus is positioned remains elusive. Here we show that several cell-cycle mutants that arrest in mitosis all displace the nucleus toward one end of the cell. Intriguingly, the actin cytoskeleton is responsible for nuclear movement. Time-lapse live imaging indicates that mitosis-specific F-actin cables possibly push the nucleus through direct interaction with the nuclear envelope, and subsequently actomyosin ring constriction further shifts the nucleus away from the center. This nuclear movement is beneficial, because if the nuclei were retained in the center, unseparated chromosomes would be intersected by the contractile actin ring and the septum, imposing the lethal cut phenotype. Thus, fission yeast escapes from mitotic catastrophe by means of actin-dependent nuclear movement.
Highlights
Proper nuclear positioning is essential for the execution of a wide range of cellular processes in eukaryotic cells (Gundersen and Worman, 2013)
Mitotic arrest leads to nuclear displacement
Cut7 in fission yeast belongs to the Kinesin-5 family and plays an essential role in bipolar spindle assembly (Hagan and Yanagida, 1990; Yukawa et al, 2020)
Summary
Proper nuclear positioning is essential for the execution of a wide range of cellular processes in eukaryotic cells (Gundersen and Worman, 2013). The bipolar spindle, which pulls sister chromatids toward two opposite poles, needs to assemble in the geometrical center of the cell This ensures symmetrical positioning of the two nuclei that are reformed upon mitotic exit. A contractile actomyosin ring (CAR) formed in the middle of the cell constricts, by which two equal-sized daughter cells inherit the identical set of the chromosomes Perturbations in this process, such as biased positioning of the nucleus/chromosomes or the CAR, would result in the production of polyploid and anucleate progenies or lead to aneuploidy, potential risk factors for tumorigenesis, and various human diseases (Gordon et al, 2012; Lele et al, 2018; Shu et al, 2019; Umbreit et al, 2020; Yaguchi et al, 2018)
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