Anterior-posterior patterning in Drosophila

1. Anterior-posterior patterning in Drosophila

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

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

5. Maternal effect mutations

6. Zygotic effect mutations

7. bicoid mutant phenotype Embryo from wild-type mother Embryo from bicoid mother Wild-type Bicoid promotes anterior fates and inhibits posterior fates.

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

9. Bicoid mRNA localization in embryo (tethered to microtubules)

10. Nuclei divide without cell division in Drosophila to produce a syncytial blastoderm embryo Fig. 9.1

11. Bicoid protein gradient in syncytial blastoderm embryo - diffuses after translation from localized mRNA - protein unstable

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

13. bicoid mRNA induces head and thorax bicoid mRNA 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

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

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

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

22. Anterior-Posterior pattern formation in flies

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. Bicoid and Nanos regulate Gap gene expression Expression patterns of proteins encoded by Gap genes

26. Gap gene mutants lack different bodyregions

27. Gap gene mutants lack different bodyregions Wild type knirps Krüppel hunchback

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

30. Anterior-Posterior pattern formation in flies

32. Wild typefushi tarazu mutant Pair-rule mutants

33. Even-skipped expression pattern

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

35. eve stripe #2 activator repressor repressor Regulation of expression stripe no. 2 of Even-skipped (eve) hunchback giant Krüppel 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

37. Regulation of the even-skipped gene

38. Refinement of expression domains over time early Fushi tarazu expression late Eve, Ftz expression

39. Refined expression domains in distinct cell rows

40. Anterior-Posterior pattern formation in flies

41. Segment polarity mutants

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 0 7 1 2 3 6 4 5 Expression of segment polarity gene wingless

45. Segments and Parasegments

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

48. Intercellular feedback maintains pair-rule gene expression states =Wnt

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

50. Gradients of Wingless and Hedgehog pattern each segment