Early events of neural development Goals: 1) to discuss the origins of cells in the nervous system 2) to discuss how neural stem cells generate diverse cell types in the nervous system The next four lectures will cover: Induction (Jan 22)...emergence of the nervous system Regionalization (Jan 24)...acquisition of positional information of neural cells Discussion of a journal article (Jan 26) Cell division and cell lineage (Jan 29) Neuronal fate specification (Jan 31) Discussion of a journal article (Feb 2) We will deal with glia later in the course! 1 Outline of this lecture Control of daughter cell fates after cell division (RGC vs differentiating cell) -Notch-Delta signaling -proneural basic helix-loop-helix (bHLH) transcription factors Identity of progenitor cells influence the type of neurons that the progenitor cell produces. -regional identity (outcome of regionalization) -temporal identity (RGCs changes as they undergo asymmetric divisions) Neuronal fate can be controlled postmitotically. 2 Published online: March 17, 2014 EMBO reports Neurogenesis during vertebrate development Judith TML Paridaen & Wieland B Huttner Published online: March 17, 2014 EMBO reports Neurogenesis during vertebrate development Judith TML Paridaen & Wieland B Huttner A C Regulation of spindle orientation Symmetric division Planar Oblique Horizontal NPCA 2 NPCs C Regulation of spindle orientation Mammalian neurogenesis Drosophila neuroblast Symmetric division Planar Oblique Horizontal NPC 2 NPCs Mammalian neurogenesis Drosophila neuroblast Apical Centrosome Spindle Basal Par3/Par6/aPKC ASPM LGN/NuMA/G Miranda/Numb ApicalAdherens junctions CentrosomeCdk5rap2 SpindleInsc Basal ASPM LGN/NuMA/G Par3/Par6/aPKC MCPH1 Lis1/Ndel1 CellMiranda/Numb cortex Adherens junctions Cdk5rap2 InscDynein MCPH1 Lis1/Ndel1 Cell cortex Inheritance of fate determinants B D Dynein Asymmetric division Symmetric Asymmetric Asymmetric Inheritance of fate determinants NPCB 1 NPC + 1 Neuron D Mouse Zebrafish Symmetric Asymmetric Asymmetric Asymmetric division Splitting/ Mouse Zebrafish NPC 1 NPC + 1 Neuron Regrowth? Splitting/ Regrowth? Notch Notch Notch Notch Notch Notch RGC RGC RGC IP Neuron RGC Neuron Notch Notch Notch Notch Notch Notch ApicalRGC RGCCentrosomeRGC IPCytoplasmicNeuron RGCBasal Neuron Par3/Par6/aPKC Mother centriole Mindbomb Ccnd2 Apical Centrosome Cytoplasmic Basal Adherens junctions Daughter centriole Numb Trim32 ProneuralPar3/Par6/aPKC transcriptionMother centriole Mindbomb Ccnd2 factors promote Ciliary membrane Delta-like 1 Adherens junctions Daughter centriole Numb Trim32 Staufen2 + mRNAs Ciliary membrane Delta-like 1 Staufen2 + mRNAs Apical E Centrosomeneuronal inheritance differentiationF Notch signaling ApicalPar3/Par6/aPKC E Centrosome inheritance F Notch signaling AdherensPar3/Par6/aPKC junctions The differentiating daughter cell generated after an CentrosomeAdherens junctions ngn2 CentrosomeMother centriole asymmetricngn2 division of a RGC expresses the proneural Daughter centriole Mother centriole transcription factorngn2 Neurogenin 2 (Neurog2 or Ngn2). CiliaryDaughter membrane centriole ngn2 CytoplasmicCiliary membrane CytoplasmicMindbomb Neurogenin 2 belongs to a family of transcription Mindbomb Cell surface Cell ngn2 factors with a basic helix-loop-helix (bHLH) domain. cycle CellDelta surface Cell ngn2 Hes1 cycle ngn2 NotchDelta Hes1ngn2 ngn2 Notch Neurogenin ngn22 promotes neuronal differentiation. Activation InhibitionActivation DelaminationInhibition Delamination Neurogenin 2 promotes transcription of Tbr2, an IPC Daughter Daughter Daughtercell 1 Daughtercell 2 marker. cell 1 cell 2 What determines whether the differentiating daughter cell becomes an IPC or a neuron is not well 354 EMBO reports Vol 15 | No 4 | 2014 ª 2014 The Authors 354 EMBO reports Vol 15 | No 4 | 2014 understood. ª 2014 The Authors 3 Published online: March 17, 2014 EMBO reports Neurogenesis during vertebrate development Judith TML Paridaen & Wieland B Huttner A C Regulation of spindle orientation Symmetric division Planar Oblique Horizontal NPC 2 NPCs Mammalian neurogenesis Drosophila neuroblast Published online: March 17, 2014 EMBO reports Neurogenesis during vertebrate development Judith TML Paridaen & Wieland B Huttner A C Regulation of spindle orientation Symmetric division Planar Oblique Horizontal Apical CentrosomeNPC 2 NPCs Spindle Basal Mammalian neurogenesis Drosophila neuroblast Par3/Par6/aPKC ASPM LGN/NuMA/G Miranda/Numb Adherens junctions Cdk5rap2 Insc MCPH1 Lis1/Ndel1 Cell cortex Dynein B D Inheritance of fate determinants Asymmetric division Symmetric Asymmetric Asymmetric Mouse Zebrafish NPC 1 NPC + 1 Neuron Apical Centrosome Spindle Basal ASPM LGN/NuMA/G Splitting/ Par3/Par6/aPKC Miranda/Numb Regrowth? Adherens junctions Cdk5rap2 Insc MCPH1 Lis1/Ndel1 Cell cortex Dynein B D Inheritance of fate determinants Asymmetric division Symmetric Asymmetric Asymmetric NPC 1 NPC + 1 Neuron Mouse Zebrafish Splitting/ Regrowth? Notch Notch Notch Notch Notch Notch RGC RGC RGC IP Neuron RGC Neuron Apical Centrosome Cytoplasmic Basal Par3/Par6/aPKC Mother centriole MindbombNotch Ccnd2Notch Notch Notch Notch Notch Adherens junctions Daughter centriole NotchNumb RGC signalingTrim32RGC RGC IPandNeuron proneuralRGC Neuron bHLH Ciliary membrane Delta-likeApical 1 Centrosome Cytoplasmic Basal Staufen2 +Par3/Par6/aPKC mRNAs Mother centriole Mindbomb Ccnd2 Adherens junctions Daughter centriole Numb Trim32 Ciliary membranefactorsDelta-like 1 Apical E Centrosome inheritance F Notch signaling Staufen2 + mRNAs Par3/Par6/aPKC Apical E Centrosome inheritance Ngn2F Notch promotes signaling transcription of Delta, a ligand for Adherens junctions Par3/Par6/aPKC Notch, which is expressed in RGCs. Adherens junctions Centrosome ngn2 Centrosome ngn2 Mother centriole Mother centriole Notch signaling promotes transcription of Hes1, Daughter centriole Daughter centriole ngn2 which inhibits Ngn2ngn2 functions and promote the Ciliary membrane Ciliary membrane RGC fate. Cytoplasmic Cytoplasmic Mindbomb Mindbomb Cell surface Cell ngn2 cycle Cell Delta Hes1 Cell surface ngn2 ngn2 cycle Notch ngn2 Delta Hes1 ngn2 Activation Notch Inhibition ngn2 Delamination Activation Daughter Daughter Inhibition cell 1 cell 2 Delamination Daughter Daughter cell 1 cell 2 354 EMBO reports Vol 15 | No 4 | 2014 ª 2014 The Authors 354 EMBO reports Vol 15 | No 4 | 2014 ª 2014 The Authors 4 Notch signaling pathway 4 H. Shimojo et al. When Delta binds to Notch, �-secretase cleaves Notch, resulting in the release of intracellular domain (Notch-ICD) into the cytoplasm and into the nucleus. �-secretase Together with Rbpj and MAML, Notch activates transcription of downstream genes such as Hes1 and Hes5. Neuron Notch Signaling Oscillations in Neural Progenitors Hes inhibits proneural bHLH proteins. Shimojo et al. (2013) Fig. 1.2 The core pathway of Notch signaling. Proneural genes such as Ascl1 (also called Mash1)Hes inhibits its own expression and oscillates rapidly in a 1 Dynamic Notch Signaling 5 Hes5 occur before overt neuronal differentiation (Bettenhausen and Neurog2 (Ngn2) promote neuronal differentiation and induce the expression of Dll1, which in et al., 1995; Hatakeyama et al., 2004). We showed here that turn activates Notch signaling in neighboring cells. Notch is cleaved at the S1 site by Furin into reciprocaltwo manner with Ngn2 in neural progenitor cells. fragments that remain associated to form the functional heterodimer receptor consisting of the the Notch ligand Dll1 is expressed in an oscillatory manner by Notch extracellular domain and the transmembrane part. Upon activation of Notch, the Notch neural progenitors. It is likely that Dll1 oscillation mutually acti- intracellular domain (NICD) is released from the transmembrane domain and transferred to the vates Notch signalingNeuron in neighboring neural progenitors, thereby nucleus, where it forms a complex with the DNA-binding protein Rbpj and the transcriptionalIn differentiating cells, Hes expression disappears andmaintaining Ngn2Hes1 oscillation and these cells (Figure 8B). At one co-activator Maml. The NICD-Rbpj-Maml ternary complex induces the expression of transcrip- Notch Signaling Oscillations intime Neural point, Progenitors when the levels of Hes1 protein are high by activation tional repressor genes such as Hes1 a n d Hes5 . Hes1 and Hes5 repress the expression of proneuralexpression becomes sustained. of Notch signaling, those of Ngn2 and Dll1 expression are low genes and Dll1, thereby leading to the maintenance of neural progenitor cells (Figure 8B). About 1 hr later, the levels of Hes1 protein become low as a result of oscillation, leading to upregulation of Ngn2 et al. 2007 ) . Hes genes also repress the expression of Notch ligand genes. Notch and Dll1, which activates Notch signaling of neighboring cells ligand expression is induced by proneural genes, and therefore neurons (Figure 8B). Our data also showed that persistent Hes1 expres- express Notch ligands and inhibit neighboring cells to differentiate into neurons by Hes5 occur before overt neuronal differentiationsion in subsets (Bettenhausen of neural progenitors represses Dll1 expression activating Notch signaling. This process, called lateral inhibition, is essential to main- et al., 1995; Hatakeyama et al., 2004). Weand showed induces ectopic here that neuronal differentiation of the neighboring tain neural progenitor cells in the developing nervous system. In the absence of Notch the Notch ligand Dll1 is expressed in an oscillatorycells in the ventricularmanner by zone (Figure S10).