|Developmental and Signaling Pathways: Neurogenesis in the Optic Lobe: Neuroblast transitions|
|Apitz, H. and Salecker, I. (2014). A challenge of numbers and diversity: neurogenesis in the Drosophila optic lobe. J Neurogenet 28: 233-249. PubMed ID: 24912777|
Legend: Neurogenesis in the Optic Lobe: Neuroblast transitions Medulla neurogenesis depends on the sequential conversion of neuroepithelial (NE) cells to NBs. (A) Outer proliferation center (OPC) NE cells gradually convert into medulla NBs in a medial to lateral orientation. The advancement of the proneural wave is defined by Lethal of scute (L’sc) expression. (B) The gradual conversion of NE cells to NBs involves a switch from symmetric to asymmetric cell divisions. The transition zone consists of progenitors PII expressing L’sc and PI expressing low levels of Deadpan (Dpn). NBs express Dpn and Asense (Ase). GMCs express Ase and Prospero (Pros). Newly formed medulla neurons (mn) maintain Pros. (C) The progression of the proneural wave from medial to lateral is negatively regulated by the Notch (N) pathway and positively regulated by the epidermal growth factor receptor (EGFR) pathway. N signaling is activated in PI NE cells by Delta (Dl) in PII and by Serrate (Ser) in surface glia (sg). Dl expression is repressed by Ecdysone signaling. EGFR signaling activates Pointed P1 (PntP1) and Rhomboid (Rho), which promote the secretion of Spitz (sSpi) from PII. sSpi is also provided by a cortex glia subtype (cg) expressing the microRNA miR-8. N and EGFR signaling regulate each other. The JAK/STAT and Fat/Hippo signaling pathways provide additional negative and positive inputs, respectively. LF, lamina furrow; LPC, lamina precursor cells (Apiz, 2014).
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