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. Author manuscript; available in PMC: 2019 Apr 12.
Published in final edited form as: Science. 2018 Oct 12;362(6411):176–180. doi: 10.1126/science.aas9435

Fig.2: Temporal patterning of progenitors. A. Multipotent progenitor model of neurogenesis in the mammalian cortex. Upper panel:

Fig.2:

Asymmetric MADM clone showing the progeny of a single aRG that span each layer (II–VI) of the mouse cortex (Picture from S. Hippenmeyer (7)). Bottom panel: A common progenitor generates neurons for the different cortical layers (VI through II) sequentially in an inside-out fashion. Ikaros (Ikzf1) is an example of a TF specifying deep layer neuronal identity. Changes in TF expression in progenitors over time are shown with color changes. aRG: apical radial glia. IP: intermediate progenitor. VZ: ventricular zone. SVZ: subventricular zone. CP: cortical plate. E: embryonic day. B. Temporal patterning in Drosophila optic lobe NBs. Upper panel: Sequential expression of tTFs in Drosophila type I optic lobe NBs, specifying distinct neuronal (e.g. Mi1, Tm1, Tm3, Tm5) and glial identities in each temporal window. Cross-regulatory interactions between tTFs are shown. Bottom panel: Newly born neurons displace older siblings away from the parent NB, generating a birth order-dependent layered neuronal arrangement in the medulla cortex in third instar larvae (L3). C. Vertebrate retina. RPCs sequentially generate the seven retinal cell types in overlapping waves. The TF Ikzf1 specifies early-born fates while Casz1 specifies late born fates. RPC: retinal progenitor cell. RGC: retinal ganglion cell. HC: horizontal cell. AC: amacrine cell. C: cone. R: rod. BP: bipolar cell. MG: Müller glia. E: embryonic day. P: postnatal day.