Biology subjects

Kimura, A.

Publications and source records attributed to Kimura, A..

5 recordsLinked to original sources

bioRxiv2018

Choice between 1- and 2-furrow cytokinesis in Caenorhabditis elegans embryos with tripolar spindles

Excess numbers of centrosomes often lead to multipolar spindles, and thus probably to multipolar mitosis and aneuploidy. In Caenorhabditis elegans, approximately 70% of the paternal emb-27APC6 mutant embryonic cells contained more than 2 centrosomes and formed multipolar spindles. However, only 30% of the cells with tripolar spindles formed 2 cytokinetic furrows. The rest formed 1 furrow, like normal cells. To investigate the mechanism how the cells avoided to form 2 cytokinetic furrows even with a tripolar spindle, we conducted live-cell imaging in emb-27APC6 mutant cells. We found that the chromatids were aligned only on 2 of the 3 sides of the tripolar spindle, and the angle of the tripolar spindle relative to the long axis of the cell correlated with the number of cytokinetic furrow. Our numerical modeling showed that the combination of cell shape, cortical pulling forces, and heterogeneity of centrosome size determines whether cells with tripolar spindle form 1 or 2 cytokinetic furrows.

cell biology↗

bioRxiv2018

Impaired chromosome segregation results in sperms with excess centrosomes in emb-27APC6 mutant C. elegans

The anaphase-promoting complex (APC) is a major regulator of chromosome segregation and is implicated in centriole engagement, whose de-regulation causes abnormal number of centrosomes. The emb-27 gene in C. elegans encodes a subunit of APC. The paternal emb-27 mutant was reported to show cell division with multiple furrows, suggesting the presence of excess centrosomes. In this study, we examined the number of centrosomes and the mechanism underlying de-regulation of centrosome number in emb-27 mutants. Our observations indicated excess centrosomes in emb-27 sperms, which resulted in zygotes with excess centrosomes. Further, the secondary spermatocyte of emb-27 produced reduced number of spermatids, which is likely the direct cause of the excess number of centrosomes per sperm. We propose that a chromosome segregation defect in emb-27 induced centrosome separation defect, resulting in reduced number of buds. Additionally, treatment with cytoskeletal inhibiting drugs indicated presence of three kinds of forces working in combination to move the centrosomes into the spermatids. The present study suggested a novel role of microtubule in the budding cytokinesis of spermatocytes.

cell biology↗

bioRxiv2018

Microinjection into the Caenorhabditis elegans embryo using an uncoated glass needle enables cell lineage visualization and reveals cell-non-autonomous adhesion control

Microinjection is a useful method in cell biology, with which exogenous substances are introduced into a cell in a location- and time-specific manner. The Caenorhabditis elegans embryo is an important model system for cell and developmental biology. Applying microinjection to the C. elegans embryo had been difficult due to the rigid eggshell surrounding the embryo. In 2013, microinjection method using a carbon-coated quartz needle for the C. elegans embryo was reported. To prepare the needle, unfortunately, special equipment is required and thus a limited number of researchers can use this method. In this study, we established a method for the microinjection of drugs, dyes, and microbeads into the C. elegans embryo using an uncoated glass needle that can be produced in a general laboratory. This method enabled us to easily detect cell lineage up to adult stages by injecting a fluorescent dye into a blastomere. We also found a cell-non-autonomous control mechanism of cell adhesion; specifically, the injection of an actin inhibitor into one cell at the 2-cell stage enhanced adhesion between daughter cells of the other cell. Our microinjection method is expected to be used for broad studies and could facilitate various discoveries using C. elegans.

cell biology↗

bioRxiv2017

The tumor suppressor APC is an attenuator of spindle-pulling forces during C. elegans asymmetric cell division

The adenomatous polyposis coli (APC) tumor suppressor has dual functions in Wnt/{beta}-catenin signaling and accurate chromosome segregation, and is frequently mutated in colorectal cancers. Although APC contributes to proper cell division, the underlying mechanisms remain poorly understood. Here we show that C. elegans APR-1/APC is an attenuator of the pulling forces acting on the mitotic spindle. During asymmetric cell division of the C. elegans zygote, a LIN-5/NuMA protein complex localizes dynein to the cell cortex to generate pulling forces on astral microtubules that position the mitotic spindle. We found that APR-1 localizes to the anterior cell cortex in a Par-aPKC polarity-dependent manner and suppresses anterior centrosome movements. Our combined cell biological and mathematical analyses support the conclusion that cortical APR-1 reduces force generation by stabilizing microtubule plus ends at the cell cortex. Furthermore, APR-1 functions in coordination with LIN-5 phosphorylation to attenuate spindle pulling forces. Our results document a physical basis for spindle-pulling force attenuation, which may be generally used in asymmetric cell division, and when disrupted potentially contributes to division defects in cancer.\n\nSignificance StatementAPC (adenomatous polyposis coli) is a Wnt signaling component as well as a microtubule-associated protein, and its mutations are frequently associated with colorectal cancers in humans. Although APC stabilizes microtubules (MTs), its mechanical role during cell division is largely unknown. Here we show that APC is an attenuator of forces acting on the mitotic spindle during asymmetric cell division of the C. elegans zygote. We performed live-imaging, laser-microsurgery, and numerical simulation to show how APC suppresses spindle pulling force generation by stabilizing microtubule plus-ends and reducing microtubule catastrophe frequency at the cell cortex. Our study is the first to document a mechanical role for the APC protein, and provides a physical basis for spindle-pulling force attenuation.

cell biology↗

bioRxiv2017

An Anisotropic Attraction Model For The Diversity And Robustness Of Cell Arrangement In Nematodes

In early embryogenesis stages in animals, cells are arranged into a species-specific pattern in a robust manner. The cell arrangement patterns are diverse, even among close relatives. We evaluated how the diversity and robustness are achieved in developing embryos. We succeeded in reproducing different patterns of cell arrangements observed in various nematode species using Caenorhabditis elegans embryos by changing the eggshell shapes. This implies that the diversity of cell arrangements can be explained by differences in a shape parameter. Additionally, we found that the cell arrangement was robust against eggshell deformation. Computational modeling revealed that, in addition to repulsion forces, attraction forces are sufficient for this robustness. Genetic perturbation experiments demonstrated that attraction forces derived from cell adhesion are necessary for the robustness. The proposed model accounts for both diversity and robustness of cell arrangements and contributes to our understanding of how diversity and robustness are achieved in developing embryos.

cell biology↗