Asymmetric cell division is a fundamental and unique feature of stem cells, where asymmetry can manifest itself in two ways – by the unequal segregation of cell-fate determinants and by the generation of differently sized daughter cells. The ability of stem cells to divide asymmetrically plays a crucial role during the development of multicellular organisms. Many of the molecular mechanisms responsible for the asymmetric mode of stem cell division have been discovered in recent years. In particular, the mitotic spindle apparatus is found to form a critical aspect of this process, as its orientation determines the axis of cell division and consequently determines whether asymmetrically localized cell-fate determinants are segregated asymmetrically or symmetrically. The process of spindle positioning can be broadly partitioned into two main phases. The first phase involves several evolutionally conserved upstream signaling players that specify an axis of polarity along which division occurs. The subsequent phase is performed by downstream physical players that set this “plan” into motion, and involves a number of cortical proteins, motor proteins and microtubule-associated proteins (MAPs). Intriguingly, recent studies suggest that the spindle apparatus is not just a downstream effector of such cell polarity proteins, but has autonomous roles in polarity establishment as well as spindle positioning. In this thesis, I will discuss the regulation and role of the mitotic spindle in asymmetric cell division, taking the well-studied Drosophila neuroblast as a primary example, with other model systems discussed as appropriate
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