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Anterior-posterior patterning in Drosophila

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Presentation on theme: "Anterior-posterior patterning in Drosophila"— Presentation transcript:

1 Anterior-posterior patterning in Drosophila

2 The fly body plan: Each segment has a unique identity
3 head The fly body plan: Each segment has a unique identity and produces distinct structures 3 thorax 8 abdomen

3 Figures\Chapter09\DevBio7e09053.jpg

4 Mutations affecting the antero-posterior axis
3 independent maternal systems: anterior, posterior, terminal fate map larva triple mutants active systems active systems wild-type A P T single mutants double mutants - P T - P - anterior bicoid A - T - - T posterior oskar A P - A - - terminal torso additive phenotypes

5 Maternal effect mutations
Figures\Chapter09\DevBio7e09t010.jpg

6 Zygotic effect mutations
Figures\Chapter09\DevBio7e09t020.jpg

7 bicoid mutant phenotype
Embryo from wild-type mother Embryo from bicoid mother Figures\Chapter09\DevBio7e09130.jpg Wild-type Bicoid promotes anterior fates and inhibits posterior fates.

8 Anterior: bicoid is required for head and thorax
Wild type bicoid mutant blastoderm fate map head + thorax abdomen abdomen

9 Bicoid mRNA localization in embryo (tethered to microtubules)
Figures\Chapter09\DevBio7e09141.jpg

10 Nuclei divide without cell division in Drosophila to produce a syncytial blastoderm embryo
Figures\Chapter09\DevBio7e09010.jpg Fig. 9.1

11 Bicoid protein gradient in syncytial blastoderm embryo
- diffuses after translation from localized mRNA - protein unstable Figures\Chapter09\DevBio7e09142.jpg

12 Transplantation of egg cytoplasm
An organizer of the anterior-posterior pattern is located at the anterior pole wt rescue of pattern wt head in the center polarity reversal wt thorax at posterior pole polarity reversal abdomen only polarity normal

13 bicoid mRNA induces head and thorax
bicoid (bcd) gene encodes a homeo-domain transcription factor

14 Injection of bicoid mRNA:
anterior (head) structures at site of injection & reorganization of polarity no head

15 Figures\Chapter09\DevBio7e09152.jpg

16 Bicoid protein: transcriptional and translational regulator
zygotic target genes maternal target mRNA (promotes anterior fates) (inhibits posterior fates)

17 Transplantation of egg cytoplasm
Posterior cytoplasm also has polarizing activity wt rescue of pattern wt head in the center polarity reversal wt thorax at posterior pole polarity reversal wt double abdomen polarity reversal abdomen only polarity normal

18 Mutations affecting the antero-posterior axis
3 independent maternal systems: anterior, posterior, terminal fate map larva triple mutants active systems active systems wild-type A P T single mutants double mutants - P T - P - anterior bicoid A - T - - T posterior oskar A P - A - - terminal torso additive phenotypes

19 Nanos is the maternal effector of the posterior system
mutant rescued rescued rescue of all posterior-system mutants by injection of nanos mRNA

20 Embryonic polarity genes
Figures\Chapter09\DevBio7e09101.jpg

21 Figures\Chapter09\DevBio7e09102.jpg

22 Anterior-Posterior pattern formation in flies
Figures\Chapter09\DevBio7e09081.jpg

23 The Bcd gradient is converted into domains of gene expression
Bcd protein binds differentially to enhancers of target genes Different thresholds of Bcd concentration are required to turn on different genes low affinity high affinity target genes are zygotically expressed Gap genes

24 Bcd gradient and expression domains of target genes
bcd mRNA Bcd protein target genes

25 Expression patterns of proteins encoded by Gap genes
Bicoid and Nanos regulate Gap gene expression Figures\Chapter09\DevBio7e09221.jpg Expression patterns of proteins encoded by Gap genes

26 Gap gene mutants lack different body regions

27 Gap gene mutants lack different body regions
Wild type Krüppel hunchback knirps

28 The gap genes regulate each other and form domains with distinct combinations of gene expression.
Hunchback Krüppel

29 Figures\Chapter09\DevBio7e09222.jpg

30 Anterior-Posterior pattern formation in flies
Figures\Chapter09\DevBio7e09081.jpg

31 Figures\Chapter09\DevBio7e09201.jpg

32 Wild type fushi tarazu mutant
Pair-rule mutants Wild type fushi tarazu mutant Figures\Chapter09\DevBio7e09211.jpg

33 Even-skipped expression pattern

34 Modularity of the Drosophila even-skipped promoter
08_18_reporter.gene.jpg 08_18_reporter.gene.jpg

35 Regulation of expression stripe no. 2 of Even-skipped (eve)
hunchback giant eve stripe #2 Krüppel repressor activator parasegment 1 2 3 4 5 multiple binding sites in enhancer of eve repressors activators

36 Regulation of the Second Stripe of Transcription from the even-skipped Gene
Figures\Chapter09\DevBio7e09242.jpg

37 Regulation of the even-skipped gene
Figures\Chapter09\DevBio7e09230.jpg

38 Fushi tarazu expression
Refinement of expression domains over time early Fushi tarazu expression Figures\Chapter09\DevBio7e09250.jpg late Eve, Ftz expression

39 Refined expression domains in distinct cell rows

40 Anterior-Posterior pattern formation in flies
Figures\Chapter09\DevBio7e09081.jpg

41 Segment polarity mutants
Figures\Chapter09\DevBio7e09202.jpg

42 Segment polarity mutants

43 Wingless signaling specifies cell fates in
the ventral epidermis Anterior cells make Hair Posterior cells make Naked cuticle Wild type arm mutant

44 Segment polarity genes – 14 stripes
13 12 A 11 ap 10 L fg 9 hg 8 1 7 2 3 6 4 5 Expression of segment polarity gene wingless

45 Segments and Parasegments
Figures\Chapter09\DevBio7e09190.jpg

46 The Even-skipped and Fushi tarazu pair-rule transcription factors activate the segment-polarity gene Engrailed

47 Intercellular feedback maintains pair-rule gene expression states
Figures\Chapter09\DevBio7e09262.jpg

48 Intercellular feedback maintains pair-rule gene expression states
=Wnt Figures\Chapter09\DevBio7e09263.jpg

49 Wnt signaling pathway - + - + - + + - - + - +

50 Gradients of Wingless and Hedgehog pattern each segment

51 Anterior-Posterior pattern formation in flies
Figures\Chapter09\DevBio7e09081.jpg


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