UC Berkeley

Cell division is crucial to life. Across all eukaryotes, this dramatic and complex process relies on the mitotic spindle to segregate chromosomes faithfully into new daughter cells, ensuring the health and survival of the next generation. Despite its conserved components and universal function of transmitting a complete genome, the cell division machinery, including the central mitotic spindle, varies widely across the tree of life in size and morphology. Interestingly, chromosome segregation defects, genome elimination, and embryonic lethality are frequently observed upon hybridization of closely related species. However, whether and how divergent cell division machinery leads to functional defects is unknown. This dissertation is comprised of four projects that span comparative evolutionary, cell, and developmental biology to examine the basis and consequences of divergent cell division machineries by using X. laevis, X. tropicalis, and X. borealis frogs. I develop the use of X. borealis to understand divergence in spindle assembly mechanisms and examine how spindle architecture varies even among closely related frog species. I adapt expansion microscopy for Xenopus extract systems, combining an unparalleled in vitro physiological reconstitution system with high-resolution imaging to measure and dissect microtubule organization to better define spindle morphometrics. We leverage the full power of the Xenopus systems to establish the most tractable vertebrate model for investigating the cellular and molecular mechanisms underlying hybridization outcomes, incompatibility, and genome elimination. Altogether, this work provides important molecular insight and understanding to mechanisms that contribute to spindle assembly and scaling, hybrid inviability, and speciation.