Cell division has fascinated cell biologists for more than a hundred years. Among many good reasons for this fascination is that mitosis and cytokinesis are beautiful to watch: M phase undoubtedly represents the most dramatic phase of the entire cell cycle, and most cellular structures undergo profound reorganizations. In all eukaryotic organisms, including fungi, plants and animals, a microtubule (MT)-based spindle apparatus is assembled and used for chromosome segregation. Similarly, cytokinesis results from a cooperation between two major cytoskeletal systems, one based on MTs, the other on actin filaments. However, a detailed comparison of mitosis in evolutionarily distant organisms, or even the study of different cell types within one and the same organism, reveals many variations on these common themes. This article will focus primarily on mitosis and cytokinesis in animal cells, such as they can typically be observed in tissue culture. Where appropriate, attention will be drawn to distinguishing features of cell division in fungi and plants, and to specialized divisions in early embryos, but prokaryotic divisions will not be considered
These dividing cells were stained by fluorescence techniques to reveal the state of chromosomes, MTs and centrosomes.
Microscopic observation of plant and animal cell division has led to a traditional subdivision of mitosis into five phases: prophase, prometaphase, metaphase, anaphase and telophase. Cytokinesis may be considered as a sixth phase that completes cell division. It begins during anaphase of mitosis and its completion marks the end of M phase (These subdivisions are useful but should not distract from the fact that cell division is a continuous process and that individual events are highly coordinated in both time and space.
During prophase, interphase chromatin condenses into well-defined chromosomes (each of these chromosomes has undergone replication during the preceding S phase, and therefore consists of two sister chromatids...