Computational modeling and measurement of mitotic spindle length control, stability and elongation

About This Grant

Summary Biological size control is of broad importance to all processes of life. Among cytoskeletal assemblies, proper chromosome segregation depends on regulated, stable length of the metaphase spindle and elongation in anaphase B. While the interplay of force and biochemical regulation is central to understanding the spindle, our understanding of this interplay is limited. As a result, we still lack a predictive theory of spindle regulation. One notable knowledge gap is the role of the nuclear envelope in closed mitosis, wherein the spindle segregates chromosomes within the intact nucleus. Nuclear envelope remodeling is essential for proper chro- mosome segregation, and increasing evidence suggests that the envelope can exert significant force on the spindle. However, we currently do not know what sets the magnitude of this force, nor nuclear envelope con- tributions to spindle regulation. Our recent model implementation has opened up simulation of spindle-nuclear envelope coupling, enabling the proposed project. The central objective of this study is to determine the inter- play between force and biochemistry responsible for regulated spindle length, stability, and elongation in closed mitosis. Aim 1: Identify the mechanisms by which force and biochemistry regulate the metaphase spindle. Aim 2: Determine the mechanisms by which force and biochemistry regulate spindle elongation. This project is significant because it will identify new principles of spindle regulation, using a minimal, geneti- cally tractable system to uncover conserved physical principles of cytoskeleton-nucleus coupling. The results will advance understanding of how physical and molecular constraints shape cytoskeletal assemblies. Insights from this project will inform related research on organelle remodeling, shape sensing, and compartmentaliza- tion. It will also develop cutting-edge modeling tools for the cytoskeleton and nuclear envelope. This project is innovative because while spindle regulation has been studied previously, we will test novel idea that the nuclear envelope and spindle mechanical interactions are important for spindle regulation in closed mitosis. In addition, we will elucidate the mechanisms of spindle stability, healing, and response to envelope force, which have seen little previous study. The project will develop state-of-the-art computational models of spindle regulation, create new fission-yeast spindle and NE mutants and protocols for spindle perturbation, and integrate multiple advanced assays to perturb and quantify spindle dynamics. This project will elucidate the sensing of and feedback between biochemistry and spindle-generated and nuclear envelope forces. Mitotic spindle defects can lead to chromosome missegregation and genome instability, con- tributing to cancer, developmental disorders, and degenerative disease. Mutations that alter nuclear envelope morphology are associated with disease states such as muscular dystrophy, and disruption of nuclear integrity can cause DNA damage and is also associated with cancer. This project will add to our understanding of the underlying cellular mechanisms contributing to these health conditions.