Partitioning of cytoplasmic organelles during mitosis with special reference to the Golgi complex.

ABSTRACT

During mitosis, not only the genetic material stored in the nucleus but also the constituents of the cytoplasm should be equally partitioned between the daughter cells. For this sake, the dividing cell goes through an extensive structural reorganization and transport along the endocytic and exocytic pathways is temporarily arrested. Early in prophase, the radiating array of cytoplasmic microtubules disassembles and the membrane systems of the secretory apparatus start to split up. In metaphase, the nuclear envelope fragments and the condensing chromosomes associate with the forming mitotic spindle. The cisternal and tubular elements of the endoplasmic reticulum and the Golgi complex break down into small vesicles, presumably as the result of an imbalance between vesicle budding and fusion. In anaphase, the two sets of chromosomes are pulled apart and a cleavage furrow forms halfway between the spindle poles. Since most organelles occur in multiple and widely dispersed copies at this stage, they will be evenly distributed between the daughter cells. During telophase and cytokinesis, the preceding fragmentation process is reversed. A nuclear envelope reappears around the chromosomes and cytoplasmic microtubules reassemble. The endoplasmic reticulum is rebuilt as a continuous system of flattened cisternae and tubules. Stacks of Golgi cisternae arise from small vesicles and are rearranged in an interconnected network. In parallel, the biosynthetic functions of the cell are normalized and intracellular membrane traffic is resumed.