Gene networks

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Drosophila embryonic development
Dorsal
Posterior
Anterior
Ventral
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The Drosophila Egg

• Inherent A/P and D/V axes of asymmetry
• These axes aligned with the A/P and D/V axes of
  the embryo
• Parts
• Egg cell
• Vitelline membrane
• Chorion

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The germline cells

• A single germline stem cell divides to form
  another stem cell and a differentiating germline
  cystoblast
• The cystoblast undergoes 4 synchronous incomplete
  mitoses to form a cyst of 16 cells connected by
  intercellular bridges (ring canals)
• One of these cells is selected as the oocyte --
  this will become the egg cell
• The other 16 cells become trophic nurse cells
  and enter endoreplicative cell cycles to become
  polyploid -- these cells synthesize RNAs and
  proteins that are later transported to the oocyte

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bicoid (bcd) and oskar (osk)

• bicoid
• The anterior morphogen for embryonic anterior
  posterior patterning
• mRNA synthesized in the nurse cells is
  transported into the oocyte and localized to the
  anterior cortex
• oskar
• The germ plasm determinant responsible for
  localizing the formation of the germ plasm,
  including the posterior morphogen nanos
• mRNA synthesized in the nurse cells and
  transported into the oocyte where it is localized
  to the posterior pole

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You should know this but a reminder.

• Transcription DNA mRNA
• Translation mRNA Protein
• italics gene, mutant or mRNA eg bcd
• Upper Case First Letter And Not Itlaics Protein
  eg Bcd

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Hierarchy
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Significance of RNA and protein localization to
the oocyte
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Localized bcd mRNA serves as a source for a
gradient of Bcd in the embryo
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Evidence of importance of bcd
Mutant bcd-
Posterior
Anterior
Wild type
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Increasing amounts of Bcd protein
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French Flag Model
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Bicoid Protein represses caudal mRNA translation
Caudal
Bicoid
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Hunchback promoter
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Hunchback promoter
hb
Bcd protein
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Diffusion of Bcd protein
Gradient of Hb protein
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Transcription factor protein concentration and
affinity
binding - no binding



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Nanos protein suppresses translation of hunchback
mRNA
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Terminal Organisation torso and tailless
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hunchback
giant
Kruppel
knirps
tailess
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Activation and Repression of Kruppel
Wild type
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Gap - Kruppel
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Hunchbackb Kruppel
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Hunchback Kruppel Giant
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Even skipped Ftz
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Evenskipped
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Pair rule genes
even skipped (eve)
1 2 3 4 5 6 7
eve stripe 2
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Syncitium (nuclei share same cytoplasm)
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Further Reading
Wolpert 2nd edition p 143-165 Gilbert 7th edition
p 264-276 Tutorial 1