Nucleolar size regulates nuclear envelope shape in Saccharomyces cerevisiae

Nuclear shape and size are cell type-specific. Change in nuclear shape is seen during cell division, development, and pathology. The nucleus of S. cerevisiae is spherical in interphase and becomes dumb-bell shaped during mitotic division to facilitate the transfer of one nucleus to the daughter cell. As yeast cells undergo closed mitosis, the nuclear envelope remains intact throughout the cell cycle. The pathways that regulate nuclear shape are not well characterized. The nucleus is organized into various sub-compartments, with the nucleolus being the most prominent. We have initiated a candidate-based genetic screen for nuclear shape abnormalities in S. cerevisiae to ask if the nucleolus influences the nuclear shape. We find that increasing nucleolar volume triggers a non-isometric nuclear envelope expansion resulting in an abnormal nuclear envelope shape. We further show that the tethering of rDNA to the nuclear envelope is required for the appearance of these extensions.