Biology subjects

Kletter, T.

Publications and source records attributed to Kletter, T..

3 recordsLinked to original sources

bioRxiv2026

Microtubule occupancy at kinetochores links checkpoint silencing with mitotic memory

The spindle assembly checkpoint (SAC) promotes faithful chromosome segregation by delaying mitosis until all kinetochores attach to spindle microtubules. Paradoxically, a p53-dependent memory mechanism--the mitotic stopwatch" --blocks daughter cell proliferation after unusually prolonged mitoses. How the SAC coordinates with the mitotic stopwatch remains unknown. Here, we found that microtubule occupancy at kinetochores is a cornerstone linking SAC silencing with mitotic memory. By combining live-cell with super-resolution microscopy, FRAP, laser microsurgery, biochemistry and molecular perturbations in Indian muntjac fibroblasts, we show that SAC silencing at kinetochores is gradual, non-uniform and confined to highly-localized microtubule attachments. Augmin promotes timely SAC silencing with high microtubule occupancy at kinetochores, whereas MPS1/CDK1 inhibition bypasses this requirement. Conversely, low microtubule occupancy delays SAC silencing, increases segregation errors and blocks daughter cell proliferation due to mitotic stopwatch surveillance. Thus, timely SAC silencing with high microtubule occupancy avoids "bad memories" of mitosis to allow daughter cell proliferation.

cell biology↗

bioRxiv2024

Cell State-Specific Cytoplasmic Material Properties Control Spindle Architecture and Scaling

Mitotic spindles are dynamically intertwined with the cytoplasm they assemble in. How the physicochemical properties of the cytoplasm affect spindle architecture and size remains largely unknown. Using quantitative biochemistry in combination with adaptive feedback microscopy, we investigated mitotic cell and spindle morphology during neural differentiation of embryonic stem cells. While tubulin biochemistry and microtubule dynamics remained unchanged, spindles changed their scaling behaviour: in differentiating cells, spindles were significantly smaller than those in equally-sized undifferentiated stem cells. Integrating quantitative phase imaging, biophysical perturbations and theory, we found that as cells differentiated, their cytoplasm became more dilute. The concomitant decrease in free tubulin activated CPAP (centrosomal P4.1-associated protein) to enhance the centrosomal nucleation capacity. As a consequence, in differentiating cells, microtubule mass shifted towards spindle poles at the expense of the spindle bulk, explaining the differentiation-associated switch in spindle architecture. This study shows that cell state-specific cytoplasmic density tunes mitotic spindle architecture. Thus, we reveal physical properties of the cytoplasm as a major determinant in organelle size control.

cell biology↗

bioRxiv2021

Volumetric morphometry reveals mitotic spindle width as the best predictor of spindle scaling

The function of cellular structures at the mesoscale is dependent on their geometry and proportionality to cell size. The mitotic spindle is a good example why length and shape of intracellular organelles matter. Spindle length determines the distance over which chromosomes will segregate and spindle shape ensures bipolarity. While we still lack a systematic and quantitative understanding of subcellular morphometrics, new imaging techniques and volumetric data analysis promise novel insights into scaling relations across different species. Here, we introduce Spindle3D, an open-source plug-in that allows for the quantitative, unbiased, and automated analysis of 3D fluorescent data of spindles and chromatin. We systematically analyse different cell types, including somatic cells, stem cells and one-cell embryos across different phyla to derive volumetric relations of spindle, chromatin, and cell volume. Taken together, our data indicate that mitotic spindle width is a robust indicator of spindle volume, which correlates linearly with chromatin and cell volume both within single cell types and across metazoan phyla.

systems biology↗