Analysis of cytoskeleton in the cells involved in cytomixis: the migrated chromatin displays an MT-organizing activity and can interact with the spindle

Abstract

The structure of cytoskeleton in the tobacco male meiocytes involved in the migration of nuclei between cells (cytomixis) is studied. The tubulin and actin components of cytoskeleton are examined using specific antibodies and phalloidin. The presence of microtubules and actin filaments inside cytomictic channels directly when the nuclei migrate through these channels is demonstrated for the first time. The actin and tubulin cytoskeleton is shown to retain its reticular structure in early prophase I before the beginning of cytomixis, during nuclear migration, and after completion of this process and emergence of micronuclei in the cytoplasm of recipient cells. It is demonstrated that if migration takes place in late prophase I, the nucleus leaves the perinuclear tubulin cage, encompassing it at this stage. After migration, the cytomictic micronuclei in recipient cell reside beyond the perinuclear tubulin cage in both meiotic prophase I and II. A microtubule-organizing activity of the migrated chromatin in meta-telophase I and II is demonstrated for the first time as well as the ability of this chromatin to form independent minispindles and radial microtubule arrays and contact the spindle of recipient cell. The role of cytomixis in production of aneuploid and unreduced pollen is discussed.