|Developmental and Signaling Pathways: Neurogenesis in the Optic Lobe: Transitions in gene expression|
|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: Transitions in gene expression Temporal patterning of medulla NBs and Notch (N) signaling contribute to the generation of diverse neuron subtypes. (A) NE cells gradually convert into NBs. As medulla NBs age, they sequentially express the transcription factors Homothorax (Hth), Eyeless (Ey), Sloppy paired 1 and 2 (Slp), Dichaete (D), and Tailless (Tll). Each NB produces a column of medulla neurons. Progeny maintain the expression of the determinant present in the NB at the time of their birth. Older NBs and their offspring are located more medially. In each lineage, the oldest neurons are positioned closest to the medulla neuropil. Klumpfuss (Klu) is expressed in NBs but not in progeny and therefore has not been included in this schematic. Interim stages, during which NBs express more than one factor and neurons downregulating factors are also not shown. (B) Ey, Slp, and D are required for the transition to the next determinant. Slp, D, and Tll are necessary to repress the preceding factor in the series. Tll is sufficient but not required to repress D (dashed line). (C) N-mediated binary cell fate choices further diversify lineages. Progeny, in which N signaling is on, express Apterous (Ap). Depending on the combination of transcription factors present, the expression of subtype-identity determinants such as Brain-specific homeobox (Bsh), Runt (Run), Drifter (Dfr), or Twin of Eyeless (Toy) is induced. Lineages defined by the combinatorial expression of these determinants give rise to specific neuronal subtypes. Tll-positive NBs generate Reversed polarity (Repo)-positive glia. Dm, distal medulla neurons; Mi, medulla intrinsic neurons; Tm, transmedullary neurons; TmY, transmedullary Y neurons (Apiz, 2014).
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