Cytokinetic morphodynamics: dissecting the molecular and mechanical control of cell division

In animal cells, cell division is driven by a series of precisely orchestrated shape changes that couple the segregation of genetic material to cytokinesis, the physical separation of the two daughter cells. Understanding the molecular and mechanical processes underlying cytokinesis has fascinated biologists for decades. Much attention has focused on the mechanics of the actomyosin cortex, a thin submembranous network of F-actin and actin-binding proteins. Myosin motors generate contractile tension in the cortical network, and their accumulation at the equator is thought to drive the cleavage of the mother cell during cytokinesis. Equatorial cortex accumulation is associated with at least partial alignment of actin and myosin into a ring-like structure, an organisation thought to promote force generation. However, the extent of this alignment and its importance for cytokinetic mechanics remain unclear. Furthermore, changes in surface tension are coupled to changes in cell volume, which increases at mitotic entry and decreases progressively as the furrow forms and ingresses. Volume changes likely also change cytoplasmic mechanical properties, but how this affects cytokinetic mechanics has not been investigated. Finally, plasma membrane reorganisation and changes in intercellular adhesions also likely contribute to cytokinetic mechanics. Taken together, increasing evidence points to the importance of considering the mechanics of the cell as a whole to understand the dynamic shape changes underlying cytokinesis. This proposal aims to leverage recent developments in advanced imaging, cellular mechanics, and image analysis to interrogate the interplay of the mechanical properties of various cellular components during cytokinesis, and to ask how together, they drive robust shape changes underlying daughter cell separation. We will focus on four aims: -Aim 1 will explore the use of morphometric analysis to analyse mitotic shape changes. In this approach, cell shape is quantified through a large number of features, which are then mapped into a low-dimensional “morphospace” using dimensionality reduction. We will then integrate morphospace analysis with quantifications of the distributions of F-actin and myosin to generate morphomolecular trajectories of cytokinesis. -Aim 2 will characterise spatiotemporal changes in the mechanical properties of cellular components during cytokinesis. We will map mechanical changes onto morphomolecular trajectories to provide hypotheses for the role of cortical tension, membrane tension, and cytoplasmic mechanics in shape change. -Aim 3 will investigate the molecular and biophysical mechanisms controlling cytokinetic shape changes. We will determine how perturbation of key cytoskeletal proteins and the contractile ring affect morphomolecular trajectories. We will then perturb volume regulation and the control of membrane tension to determine their respective contributions to mitotic morphogenesis. -Aim 4 will examine the mechanics of cell division in epithelia, where cells must maintain barrier function while changing shape. We will quantify forces arising at intercellular junctions throughout cytokinesis using DNA hairpins as sensors. We will incorporate these resistive forces into our computational simulations and interrogate potential mechanoresponsive feedbacks during cytokinesis in an epithelial context. Finally, we will probe the biophysical limits of the trade-off between achieving robust cytokinesis and preserving barrier integrity by modulating the strength of intercellular adhesions with DNA nanotechnology. Together, our research will generate a holistic understanding of the multiple mechanical processes that participate in mitotic morphogenesis and will dissect the molecular mechanisms controlling force generation and shape change dynamics required for robust and successful cell division.