Cell division is an essential process required for all living beings, by which a parent cell divides into two or more daughter cells. As one type of cell division, asymmetric cell division is a phenomenon that has long been studied, especially in the developing nervous system of invertebrates and vertebrates. Asymmetric cell division is a mechanism whereby any given cell divides to give rise to two daughter cells, each of which possesses a different fate than the other. Such “fates” can be manifested as differences in size, morphology, gene ex
To date there are two established modes of asymmetric cell division. One type of division, commonly referred to as a niche-controlled, or extrinsic, mechanism of cell division, emphasizes the importance of the stem cell niche. Environmental factors influence the ability to maintain the progenitor population, and a cell relies on contact with its stem cell niche to be able to self-renew. A second, intrinsic mechanism of asymmetric cell division serves as the dominant mode of division during development and will be the focus of this discussion rather than the niche-controlled mechanism. With regard to the intrinsic mechanism, regulators of self-renewal are asymmetrically localized during mitosis, so that when cells divide only one daughter cell inherits these regulators and thus takes on a different fate than its sister cell.
The major aspects of asymmetric cell division in Drosophila will be discussed at length. An apical-basal axis of polarity is set up within cells, which is used to both asymmetrically distribute self-renewal determinants and orient the mitotic spindle to polarize the determinants, is a very important feature of asymmetric cell division. The cell fate determinants of neural stem cell self-renewal and their asymmetric localization are also essential in ensuring that the divisional machinery operates correctly. Additionally, the role that mitotic spindle orientation plays in asymmetric division is tantamount to this developmental process and will also be discussed. The coordination of asymmetric protein localization with cell cycle progression is another aspect of asymmetric cell division that will be covered as well. Moreover, of great importance to this field of research is the concept that failure of asymmetric cell division to occur properly has widespread consequences, mainly that of neoplastic cellular growth and tumorigenesis.