BIOL 3010 Lecture Notes - Tx Network, Zygote

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29 Jan 2013
Outline of Lecture 07
Patterning a Simple System II
I. Overview
- Maternal genes determine A/P and D/V axes, which regulate…
- Zygotic gap genes begin to set up segmentation, which regulate…
- Zygotic pair-rule genes establish finer segments, which regulate
- Zygotic segment polarity genes establish direction of each segment
- All three zygotic gene classes regulate homeotic genes, which direct
development of each segment
II. Pair-rule Genes
- Role is to roughly establish parasegments; each pair-rule gene is expressed in
alternating parasegments
- Multiple + and – cis acting enhancers that respond to gap genes restrict
expression to stripes
- Stripe patterns are out of phase, so each row expresses different combination of
pair-rule genes
- Pair-rule genes are txn factors that control expression of segment polarity genes
A) Example 1: Expression of hairy in stripe 6
- Only a single hairy gene; different upstream regulatory sequences that control
expression in each stripe
- Hairy is activated by Knirps but is outcompeted by Kruppel repression, which
completely determines where the hairy stripe is
B) Example 2: Expression of eve in stripe 2
- Also only a single eve gene, regulation analogous to hairy
- Activated by bicoid and hunchback; repressed by giant (recall anterior expr also)
and kruppel; this determines where eve is expressed
III. Segment Polarity Genes
- Role is to establish A/P orientation of each segment through cell-cell
- Segment polarity genes encode cell signaling molecules (unlike gap and pair-
rule txn factors)
- S.P. genes are expressed identically in each segment
- Wingless and engrailed/hedgehog are expressed on opposite sides of a
parasegment boundary; they regulate each other and are interdependent
IV. Homeotic Genes
- Role is to direct development of structures specific for each segment
- Two major homeotic complexes in Drosophila: BX-C (posterior) and ANT-C
- HOX genes are txn factors that recognizes target genes through HTH motifs
- Vertebrate HOX genes
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