Biology subjects

Neahring, L.

Publications and source records attributed to Neahring, L..

4 recordsLinked to original sources

bioRxiv2023

Torques within and outside the human spindle balance twist at anaphase

At each cell division, nanometer-scale motors and microtubules give rise to the micron-scale spindle. Many mitotic motors step helically around microtubules in vitro, and most are predicted to twist the spindle in a left-handed direction. However, the human spindle exhibits only slight global twist, raising the question of how these molecular torques are balanced. Here, using lattice light sheet microscopy, we find that anaphase spindles in the epithelial cell line MCF10A have a high baseline twist, and we identify factors that both increase and decrease this twist. The midzone motors KIF4A and MKLP1 are redundantly required for left-handed twist at anaphase, and we show that KIF4A generates left-handed torque in vitro. The actin cytoskeleton also contributes to left-handed twist, but dynein and its cortical recruitment factor LGN counteract it. Together, our work demonstrates that force generators regulate twist in opposite directions from both within and outside the spindle, preventing strong spindle twist during chromosome segregation.

cell biology↗

bioRxiv2023

The oncogene cyclin D1 promotes bipolar spindle integrity under compressive force

The mitotic spindle is the bipolar, microtubule-based structure that segregates chromosomes at each cell division. Aberrant spindles are frequently observed in cancer cells, but how oncogenic transformation affects spindle mechanics and function, particularly in the mechanical context of solid tumors, remains poorly understood. Here, we constitutively overexpress the oncogene cyclin D1 in human MCF10A cells to probe its effects on spindle architecture and response to compressive force. We find that cyclin D1 overexpression increases the incidence of spindles with extra poles, centrioles, and chromosomes. However, it also protects spindle poles from fracturing under compressive force, a deleterious outcome linked to multipolar cell divisions. Our findings suggest that cyclin D1 overexpression may adapt cells to increased compressive stress, contributing to its prevalence in cancers such as breast cancer by allowing continued proliferation in mechanically challenging environments.

cell biology↗

bioRxiv2022

Kinetochore-fiber lengths are maintained locally but coordinated globally by poles in the mammalian spindle

At each cell division, nanometer-scale components self-organize to build a micron-scale spindle. In mammalian spindles, microtubule bundles called kinetochore-fibers attach to chromosomes and focus into spindle poles. Despite evidence suggesting that poles can set spindle length, their role remains poorly understood. In fact, many species do not have spindle poles. Here, we probe the poles contribution to mammalian spindle length, dynamics, and function by inhibiting dynein to generate spindles whose kinetochore-fibers do not focus into poles, yet maintain a metaphase steady-state length. We find that unfocused kinetochore-fibers have a mean length indistinguishable from control, but a broader length distribution, and reduced length coordination between sisters and neighbors. Further, we show that unfocused kinetochore-fibers, like control, can grow back to their steady-state length if acutely shortened by drug treatment or laser ablation: they recover their length by tuning their end dynamics, albeit slower due to their reduced baseline dynamics. Thus, kinetochore-fiber dynamics are regulated by their length, not just pole-focusing forces. Finally, we show that spindles with unfocused kinetochore-fibers can segregate chromosomes but fail to correctly do so. We propose that mammalian spindle length emerges locally from individual k-fibers while spindle poles globally coordinate k-fibers across space and time.

cell biology↗

bioRxiv2021

Opposing motors provide mechanical and functional robustness in the human spindle

At each cell division, the spindle self-organizes from microtubules and motors. How the spindles diverse motors, often acting redundantly or in opposition, collectively give rise to its emergent architecture, mechanics, and function is unknown. In human spindles, the motors dynein and Eg5 generate contractile and extensile stress, respectively. Inhibiting dynein or its targeting factor NuMA leads to unfocused, turbulent spindles and inhibiting Eg5 leads to monopoles, yet bipolar spindles form when both are inhibited together. What, then, are the roles of these opposing motors? Here we generate NuMA/dynein- and Eg5-doubly inhibited spindles that not only attain a typical metaphase shape and size, but also undergo anaphase. However, these spindles have reduced microtubule dynamics and are mechanically fragile, fracturing under force. Further, they exhibit lagging chromosomes and dramatic left-handed twist at anaphase. Thus, while these opposing motor activities are not required for the spindles shape, they are essential to its mechanical and functional robustness. Together, this work suggests a design principle whereby opposing active stresses provide robustness to force-generating cellular structures.

cell biology↗