1. Gradients, cascades, and signaling pathways
Chapter 31
Gradients, cascades, and signaling pathways
Development of the Drosophila body plan
Genetic studies
One of the best understood developmental systems
13,600 genes
Axis determination
Signaling pathway
Transcriptional and translational regulation
Principles of Development
2nd edition, by Lewis Wolpert (Chapter 5)
The genetics of axis specification in Drosophila
The Chapter 9 of Developmental Biology by Scott Gilbert, 7th edition
Chang-Gung University
Dr. Li-Mei Pai

2. Targeted ectopic expression of the Eyeless gene --induce eyes to develop in locations such as legs and antennae
Closely related genes initiate the development program for
the same organ in animals separate by 500 million years of evolution

3. Life cycle of Drosophila 4 stages: embryo, larva, pupa, adult
Culture condition: 250C and 60% humidity

4. Body patterning of fly One cell to an organism Fig. 31-1
Figures\Chapter09\DevBio7e09070.jpg

5. Homogeneous egg to asymmetry
---control of gene expression (spatial and temporal)
Asymmetric division
Asymmetric distribution of cytoplasmic component
Maternal genes
Segmentation genes
Homeotic genes

6. Early development
of Drosophila

7. Transgenic flies

8. Model of Drosophila Anterior-Posterior Pattern Formation
Maternal effect genes
Zygotic genes
Syncytial blastoderm
Figures\Chapter09\DevBio7e09081.jpg
Cellular blastoderm

9. Maternal effect genes—( do not damage mother)
preformed mRNA and proteins in the egg
Zygotic genes—embryo nuclei

11. Polarization of the body axes during oogenesis
each egg chamber: 3 types of cells
Oocyte with nucleus (germinal vesicle-GV)
Connected to 15 nurse cells }---germ-line
Surrounded by a monolayer of about 1000 somatic follicle cells

12. Female sterile mutation
Somatic cells
Germline cells
Genetic analyses
Biochemical assays

13. Fig. 31-4

14. The effects of mutations in the maternal gene system
Three classes
Anterior
Posterior
terminal
head and thoracic
abdominal
acron and telson

15. Three independent Genetic Pathways Interact to Form the Anterior-Posterior Axis of the Drosophila Embryo
Figures\Chapter09\DevBio7e09101.jpg

16. Three independent Genetic Pathways Interact to Form the Anterior-Posterior Axis of the Drosophila Embryo
Figures\Chapter09\DevBio7e09102.jpg

18. Morphogen----cell structure
Quantitative---qualitative

19. Bicoid gene is necessary for the establishment of the anterior structure
Bicoid--Transcribed in nurse cells,
transported into the oocyte,
localized at the anterior( 3’UTR)
fertilized—translated
Protein diffuses and forms
morphogen gradient
No head and thoracic
If prick at the anterior of normal egg
Partial rescued
Bicoid mutant +
wt anterior cytoplasm—
wt head

20. Gene copy number

21. Repression of nanos mRNA
translation outside of posterior
Hb-repressor of transcription (of
Abdominal gene)
Hb is required for thorax structure,
and is absent in posterior
Nanos---prevent Hb translation—
mRNA degraded—knirps and
Giant expression

22. Posterior determination
Nanos ( and pumilio)
suppresses the translation
Of the maternal mRNA of
Hunchback
Zygotic hb establishes a
Gradient
If maternal hb is absent, nanos is
no more needed

24. Fate map
Information—maternal regulators
Refined—zygotic genes
Region—compartment
14 parasegments (gastrulation)—
Eg. 8=A2P+A3A

26. Every other segment

27. The target genes of hunchback
Increase dose of hunchback –
kruppel shift posteriorly
Gap: 1) respond to the Bicoid
2) regulate one another

29. Phenotype of
pair rule mutant

30. Expression of
pair rule gene

31. Regulation of
pair rule genes

32. Pair rule genes The mRNA is uniformly expressed,
but protein synthesis is blocked—
specific degradation of mRNA
Stripes develop, transcription ceases
Ftz promoter respond to
other pair-rule genes
Fig

33. Segment polarity-engrailed

34. Engrailed-
transcription factor
homeodomain

35. Intercellular signaling set up PS boundary

36. Segment polarity A/P axis within one segment
Ventral epidermis of the abdomen—ventral denticle belts (anterior)
Mutation—alter the denticle pattern
Wingless=Wnt
hedgehog
Principles of Development
by Lewis Wolpert
Oxford university press
Second edition, 2002

37. Signals controlling cuticle pattern
Principles of Development
by Lewis Wolpert

38. Fig

39. Cell, 127, 469, 2006

40. Colon cancer-APC
Oncogenic-c-myc
Cell, 127, 469, 2006

41. Wg distributed asymmetrically—
less in posterior (endocytosis and degradation)
Until early stage 10, Wingless spreads into the engrailed domain and then recedes sometime during stage 10. At stage 12, Wingless-containing vesicles are infrequently detected in engrailed-expressing cells. At this stage, rhomboid begins to be expressed at the posterior of each engrailed stripe, leading to the activation of EGFR signaling in and around its domain of expression. The zone of Rhomboid influence corresponds roughly to where denticles form at the end of embryogenesis, while Wingless signaling is associated with the absence of denticles (bald cuticle). PS, parasegment boundary; SB, segment boundary.

42. Different pathways that transduce Wnt signals
Camadulin
Planar polarity-hair
pointed direction
Cell, 109, 271, 2002

43. Intercellular signaling set up PS boundary
Developmental Biology by Scott F. Gilbert
Sinauer Associates, publishers
Six edition, 2000

44. The domains of expression of the segment polarity genes
Patched is not in en cells
Principles of Development
by Lewis Wolpert

47. The hedgehog signaling pathway
Without signal—Ci is processed as a repressor
into nucleus
With signal---full length Ci acts as an activator in
the nucleus
Principles of Development
by Lewis Wolpert

48. Reading reference :
Wnt/b-Catenin signaling in Development and disease
Cell, 127, , 2006