Biology subjects

Begley, M. A.

Publications and source records attributed to Begley, M. A..

3 recordsLinked to original sources

bioRxiv2026

Age-associated changes to mouse oocyte meiotic spindle properties revealed through in situ measurements

Chromosome segregation errors in oocyte meiosis are a leading cause of early miscarriage and congenital disorders in mammals and these errors become more prevalent with advanced maternal age. Although the effects of aging on the functions of critical meiotic proteins and cytoskeletal filaments in oocytes are known, the influence of aging on the force generating capabilities of oocyte spindle components remains largely unexplored. Through the integration of a coarse-grained model and in situ experiments, we compare the long-axis mechanical properties of metaphase I (MI) and II (MII) oocyte spindles from reproductively young and old mice. Increased inter-kinetochore distance in aged MII oocytes agree with a model of age-associated cohesion loss, and kinetochore dynamics in these spindles following laser ablation suggest a similar reduction in inter-kinetochore bridge viscosity. Simultaneously, we find that both cohesive and poleward force generators lose stiffness with advanced age in MI spindles. In total, we quantify the extent to which structural spindle components lose their stiffness and viscosity during maternal aging, highlighting the multifaceted impacts of aging on mouse oocyte spindle mechanics. Significance StatementO_LIMaternal aging influences mammalian oocyte spindles in numerous ways, yet the impacts of aging on the balance of collective spindle forces remain poorly understood. C_LIO_LIIntegrating coarse-grained mechanical modeling with in situ measurements of spindle morphology and kinetochore dynamics, we quantify age-associated changes to the viscosities and elastic stiffnesses of oocyte spindle component parts. C_LIO_LIThis work provides both a characterization of the effects of aging on force production in mammalian oocyte spindles and a blueprint for future studies of spindle force generation in complex biological contexts. C_LI

cell biology↗

bioRxiv2022

Pushing the envelope: force balance in fission yeast closed mitosis

The fission yeast S. pombe divides via closed mitosis, meaning that spindle elongation and chromosome segregation transpire entirely within the complete nuclear envelope. Both the spindle and nuclear envelope must undergo significant conformation changes and exert varying forces on each other during this process. Previous work has demonstrated that nuclear envelope expansion1,2 and spindle pole body (SPB) embedding in the nuclear envelope3 are required for normal S. pombe mitosis, and mechanical modeling has described potential contributions of the spindle to nuclear morphology4,5. However, it is not yet fully clear how and to what extent the nuclear envelope and mitotic spindle each directly shape each other during closed mitosis. Here, we investigate this relationship by observing the behaviors of spindles and nuclei in live mitotic fission yeast following laser ablation. First, we characterize these dynamics in molecularly typical S. pombe spindles, finding them to be stabilized by dense crosslinking, before demonstrating that the compressive force acting on the spindle poles is higher in mitotic cells with greater nuclear envelope tension and that spindle compression can be relieved by lessening nuclear envelope tension via laser ablation. Finally, we use a quantitative model to interpret how these data directly demonstrate that fission yeast spindles and nuclear envelopes are a mechanical pair that can each shape the others morphology.

biophysics↗

bioRxiv2020

K-fiber bundles in the mitotic spindle are mechanically reinforced by Kif15

The mitotic spindle, a self-constructed microtubule-based machine, segregates chromosomes into two eventual daughter nuclei. In mammalian cells, microtubule bundles called kinetochore-fibers (k-fibers) anchor chromosomes within the spindle. Chromosome segregation thus depends on the mechanical integrity of k-fibers. Here, we investigate the physical and molecular basis of k-fiber bundle cohesion. We sever k-fibers using laser ablation, thereby detaching them from poles and testing the contribution of pole-localized force generation to k-fiber cohesion. We then measure the physical response of the remaining kinetochore-bound segments of the k-fibers. We observe that microtubules within ablated k-fibers often, but not always, splay apart from their minus-ends. Furthermore, we find that minus-end clustering forces induced in response to ablation seem at least partially responsible for k-fiber splaying. We also investigate the role of the putative k-fiber-binding kinesin-12 Kif15. We find that pharmacological inhibition of Kif15 microtubule binding reduces k-fiber mechanical integrity. In contrast, inhibition of its motor activity but not its microtubule binding does not greatly affect splaying. Altogether, the data suggest that forces holding k-fibers together are of similar magnitude to other spindle forces, and that Kif15, acting as a microtubule crosslinker, helps fortify and repair k-fibers. This feature of Kif15 may help support robust k-fiber function and prevent chromosome segregation errors.

cell biology↗