Biology subjects

Shimamoto, Y.

Publications and source records attributed to Shimamoto, Y..

3 recordsLinked to original sources

bioRxiv2023

Transition to the structurally vulnerable nuclear state is an integral part of mouse embryonic development

Upon fertilization, germ cells are reprogrammed to acquire the ability to develop into an entire organism. Whereas extensive studies have focused on epigenetic reprogramming of chromatin states during development, changes of the nucleus that surrounds chromatin are ill-defined. Here, we show that nuclei become structurally and mechanically vulnerable at the 2-cell stage during mouse embryonic development. The 2-cell stage nuclei are extraordinarily plastic and deformable in contrast to those of 1-cell and 4-cell stages. The mechanically vulnerable nuclear state is attained by autophagy-mediated loss of lamin B1 from the nuclear membrane. This developmentally programmed lamin B1 dynamics is required for chromatin organization and major zygotic genome activation. We thus demonstrate that structural reprogramming of nuclei is a major determinant of embryonic gene expression and acquisition of totipotency.

cell biology↗

bioRxiv2018

Mechanical heterogeneity and roles of parallel microtubule arrays in governing meiotic spindle length

Metaphase spindles are arrays of microtubules whose architecture provides the mechanism for regulated force generation required for proper segregation of chromosomes during cell division. Whereas long-standing models are based on continuous antiparallel microtubule arrays connecting two spindle poles and overlapping at the equator, spindles typically possess a more complex architecture with randomly arranged short filaments. How these heterogeneous multifilament arrays generate and respond to forces has been mysterious, as it has not been possible to directly measure and perturb spindle force while observing relevant filament motility. Here, we combined microneedle-based quantitative micromanipulation with high-resolution microtubule tracking of Xenopus egg extract spindles to simultaneously examine the force and individual filament motility in situ. We found that the microtubule arrays at the middle of the spindle half are considerably weak and fluid-like, being more adaptable to perturbing forces as compared to those near the pole and the equator. We also found that a force altering spindle length induces filament translocation nearer the spindle pole, where parallel microtubules predominate, while maintaining equatorial antiparallel filaments. Molecular perturbations suggested that the distinct mechanical heterogeneity of the spindle emerges from activities of kinesin-5 and dynein, two key spindle motor proteins. Together, our data establish a link between spindle architecture and mechanics, and highlight the importance of parallel microtubule arrays in maintaining its structural and functional stability.

cell biology↗

bioRxiv2017

High quality frozen extracts of Xenopus laevis eggs reveal size-dependent control of metaphase spindle micromechanics

Cell-free extracts from unfertilized Xenopus laevis eggs offer the opportunity for a variety of biochemical assays for analyzing essential cell cycle events, such as metaphase spindle assembly. However, extracts utility is often hampered by their short storage-stability duration and high quality variation. Here, we report a simple two-step method for preparing frozen egg extracts that retain spindle assembly activity levels that are close to those of freshly prepared extracts. Extract degradation associated with the freeze-thaw process can be substantially reduced by using centrifugal filter-based dehydration and slow sample cooling. Large amounts of frozen extract stocks from single batch preparations allowed us to collect a large number of data in micromanipulation experiments that are intrinsically low-throughput and, hence, clarify correlations between metaphase spindle size and stiffness. We anticipate that our method provides an assay platform with minimized biological heterogeneity and makes egg extracts more accessible to researchers as distributable material.\n\nSummaryThe authors describe a method for preparing frozen extracts of Xenopus laevis eggs that retain spindle assembly activity levels that are close to those of freshly prepared extracts. This allowed for clarifying the correlation between spindle size and stiffness.

cell biology↗