BIOL 3010 Lecture Notes - Decapentaplegic, Spatial Planning, Tx Network
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Outline of Lecture 06
Patterning a Simple System I
See 5 pages of notes in binder on “Introduction to Patterning”
I. Overview
- Much of our knowledge of A/P and D/V axis development comes from
Drosophila
- Proper spatial development is determined by differential gene expression
- Different HOX genes are expressed along the A/P axis, and this determines fate
of cells in each segment
- Interestingly, order of HOX genes in genome is same order of expression
II. Anterior/Posterior axis (A/P)
- A/P axis is established when embryo is a syncytium
- bicoid mRNA localized to anterior pole; nanos mRNA localized to posterior
pole
- Bicoid and nanos protein form opposing gradients along A/P axis as cells begin
to form
- Hunchback txn is activated by Bicoid and translation repressed by Nanos; hence,
Hunchback has a graded distribution along A/P axis
- Kruppel, knirps, and giant genes are have different thresholds for repression by
Hunchback; hence Hb sets the anterior boundary for their expression
- (There is an anterior region that expresses giant, under a different control
mechanism)
- Torso-like produced by posterior follicle cells (also some anterior follicle cells)
activates Torso receptor (found throughout oocyte) and results in txn of Tailless
- Tailless differentially represses knirps and giant, setting posterior boundaries
III. Dorsal/Ventral axis (D/V)
- D/V axis is determined by Dorsal gene product
- Dorsal is expressed in cytoplasm of all cells in oocyte
- Ventral follicle cells use secreted signals to tell Dorsal in ventral embryo cells
(or oocyte nuclei???) to translocate to nucleus; however, Gurken (produced in A-
D corner of oocyte) signals dorsal follicle cells not to send these signals
- Spatzle is such a secreted signal, which sets up a gradient along the ventral side;
Spatzle binds to its receptor Toll which signals Dorsal to translocate to nuclues
- Dorsal activates txn of Twist and Snail (so found on ventral side) and represses
Decapentaplegic, Tolloid, and Zerknult (so found on dorsal side)