Nuclear actin cable with multiple branches during yeast meiosis

Actin polymerizes to form filaments/cables for motility, transport, and structural framework in a cell. Recent studies show that actin polymers are present not only in cytoplasm, but also in nuclei of vertebrate cells, and their formation is induced in response to stress. Here, by electron microscopic observation with rapid freezing and high-pressure freezing, we found a unique polymerized form of actin inside of nuclei of budding yeast cells undergoing meiosis. The nuclear actin cable during meiosis consists of several actin filaments with a rectangular lattice arrangement and is associated with multiple branched cables/filaments showing “feather-like” appearance. The cable is immuno-labeled with anti-actin antibody and sensitive to an actin-depolymerizing drug. Like cytoplasmic actin cables, nuclear actin cables are rarely seen in pre-meiotic cells and spores, and are induced during meiotic prophase-I. We speculate that nuclear actin cables play a role in nuclear events during meiotic prophase I.