Developmental Regualtory Networks in Drosophila

Cytoplasmic determinant: establish anterior-posterior gradient of embryo
1. Bicoid- anterior
  1. Hunchback gene expression is dependent on the level of bicoid protein
    1. More bicoid= more hunchback
2. Nanos- posterior
Gap genes: Organize cells into groups of segments along anterior-posterior
1. Expression of GAP genes are regulated by Bicoid/Nanos and Torso/Torsolike genes
  1. GAP genes are differentially expressed in separate domains in the developing embryo
    1. At high levels of hb, kr expression is repressed and at threshold hb level hr is expressed
    2. At very high level of hb, kni and gt gene are repressed
    3. gt is induced at anterior side by bicoid
  2. Mutation in a single gene may have a drastic effect on the expression of downstream genes
    1. Visually, the Kruppel gene is show a thick band and the mutation will show a gradient
Pair-Rule genes: Organize cells into individual segments
1. Specify 14 parasegments
2. All of them encode TFs
  1. EVE (even-skipped) and FTZ (fuchi tarazu)
    1. EVE gene is expressed in 7 strips in the growing embryo
    2. EVE expresses in 2, 3, and 7 first
3. Express in every other segment
Segment polarity genes: establish anterior-posterior gradient within each segment
1. Specify the anterior-posterior regions of each parasegment
  1. Parasegments are based on gene expression and cannot be seen from the outside
2. some express constantly, other transiently
  1. 2 ways for continuous expression
    1. positive feedback loop
    2. Engrailed-wingless signaling pathway
      1. Expression of En stimulates Hh
        Hh becomes active and interacts with Ptc-Smo
        Hh inhibits the Ptc-Smo second- messenger pathway, allowing wg to be expressed
        Wg actsback on Frizzled activating more En production
        Ptc can suppress wg but when smo is active Ptc con't suppress wg
Homeotic genes: establish segment identity; master regulatory genes that encode TFs
1. Homeosis- a mutation that causes transformation of segment into a related segment
2. HOM- Drosphila and Hox in vertebrates
3. Encode proteins with homeodomain (interact with DNA regulatory sequences of target genes)
4. Regulation of Homeotic gene expression
  1. Always repress genes that are anteriorly expressed
Drosophila segments
1. Main body regions: Head region, Thorasic, Abdomen region
2. Larva have 14 segments
3. Homeobox complexes
  1. Antennapedia complex
    1. Regulates the development of head and thorasic region
  2. Bithorax complex
    1. Regulates the development of parasegment 5-14
      1. ubx (5-12) AbdA (7-13) AbdB (10-14)
    2. Bithorax mutation= anterior part of the haltere into anterior part of the wing
    3. Postbithorax= posterior part of the haltere into posterior part of the wing
      1. Both= complete wing in the T3 segment

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Developmental Regualtory Networks in Drosophila

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	Created by Danielle Braswell over 6 years ago