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 stripes13 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