Cytoplasmic flows caused by actomyosin contraction drive interkinetic nuclear migration

Abstract

Interkinetic nuclear migration (IKNM) is the process by which the nucleus migrates between apical and medial surfaces of pseudostratified epithelia. Previous studies have proposed force generating mechanisms, acting primarily on the nucleus. Having observed in drosophila wing discs that cytoplasmic components (lipid droplets and mitochondria) migrate alongside the nucleus, we used live imaging and particle tracking to demonstrate that the cytoplasm flows are responsible for the nucleus migration. We identify that nuclear migration in mitotic cells is preceded by a fast basal-to-apical flow of cytoplasm occurring over short time scales. We further show that, for the migration of basally located nuclei to an apical position, a slower flow of cytoplasm is responsible over a longer time scale. Our findings indicate that these flows are driven by acto-myosin contractile forces. These flows increase the hydrostatic pressure under the nucleus to exert a lifting force, much like a piston in a hydraulic cylinder.