Model for a transient amplifying progenitor cells in DM NB lineages. (a) In the canonical model of asymmetric NB division, a single neurogenic division of the small GMC progenitor cell produces two neurons (N) at each round of NB division. Unequal partitioning of Prospero promotes neurogenic division by inhibiting self-renewing factors in the GMC. (b) The DM NB divides asymmetrically without Prospero, which enables the small daughter cell to retain self-renewing potential and to behave as an IP. In this cell, expression of Prospero and unknown polarization cues re-established the asymmetric segregation of fate determinants and the generation of the neurogenic progenitor GMC. This novel mode of neurogenesis increases the number of post-mitotic neurons that individual NBs in the dorsomedial brain can generate at each round of divisions.