Brain Evolution and the Centrosome

Microtubules are cytoskeletal elements that are important for many cellular processes. Mitotic spindles that are formed for cell division are made up of microtubules. Centrosomes are cellular organelles that organize microtubules. In most cells cellular constituents are not distributed symmetrically within the cell and therefore cells exhibit distinct polarity and asymmetry. Therefore many cells have an apical side and a basal side. The microtubules also exhibit polarity along their proximal distal axis from their site of anchoring and nucleation. When a cell divides the centrosome also divides along with DNA replication. Thus each of the daughter cells will inherit a centrosome. Recent evidence suggests that the two centrosomes may not be equivalent and that the centrosome that a cell inherits may infl uence cell fate. In addition, during cell division the centrosomes are important for the alignment of the mitotic spindles and determining the plane of cell division. This in turn could impact the distribution of proteins in the dividing cell and thus confer different cell fates on the daughter cells. These aspects as they relate to neural stem cell division and regulation of neuron number are explored. In addition, the origins of the function of the mammalian centrosomes are traced.