A nuclear jamming transition in embryonic tissues

Tissue physical states as well as rigidity transitions are governed by cellular density and mechanics of cell-cell contacts but the role of subcellular organelle on tissue structures and dynamics has not been studied. Combining computational modeling and in-vivo experiments, we find a novel nuclear jamming transition governed by nuclear volume fraction and nuclear aspect ratio. By introducing nuclei as repulsive soft particles that interact with cell junctions in Active Foam model, we study how nuclei alter tissue architecture and dynamics. For isotropic nuclei, tissue dynamics progressively slow down while tissue structure becomes more ordered as nuclear volume fraction increases. As the nuclear aspect ratio increases, the nuclear jamming transition occurs at a smaller nuclear volume fraction because anisotropic nuclei start to touch cell junctions at a smaller nuclear volume fraction. For a large nuclear volume fraction and a large nuclear aspect ratio, we observe a formation of nematic domain that leads to enhanced cell movement. Structural analysis of developing eye and brain tissues in zebrafish embryo shows that these tissues undergo a nuclear jamming transition with increasing nuclear volume fraction and decreasing nuclear aspect ratio that leads to more ordered cellular arrangement. Our result shows a novel rigidity transition governed by nuclear-to-cytoplasmic ratio and nuclear geometry, which can be an important mode of phase transitions in embryonic tissues.