Neural stem and progenitor cells giving rise to neurons in developing mammalian neocortex fall into two principal classes with regard to location of mitosis-apical and basal, and into three principal classes in terms of cell polarity during mitosis-bipolar, monopolar, and nonpolar. Insight has been gained into how inheritance of polarized, apical and basal, cell constituents is related to symmetric versus asymmetric divisions of these progenitors, and how this inheritance is linked to their expansion, self-renewal, and neurogenesis. Retention and inheritance of the basal process emerge as key for self-renewal, notably for the monopolar progenitors of prospective gyrencephalic neocortex that undergo asymmetric mitoses at basal locations. The resulting expansion of the neocortex during evolution is proposed to be associated with an increased cone-shape of radial units.
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