1. BRAIN VERSUS SKIN DEVELOPMENT IN FLIES
LECTURE 7:
BRAIN VERSUS SKIN DEVELOPMENT IN FLIES

2. Hierarchy of Gene Action in D/V Patterning
High [Dorsal]
Low [Dorsal]
No Dorsal
Graded Dorsal Concentration
Created by Mother
Mesoderm Genes
Neuroectoderm Genes
Non-neural Genes
D/V Genes
Basic Tissue Types
Controlled by Embryo

3. Ventral Epidermal Genes Neural Genes
Dpp
Neuronal Genes
Brk, Sog
Dorsal Genes
AS-C
Rho
Ventral Epidermal Genes
Neural Genes
Snail
Neural Genes
Twist
Mesodermal Genes = M e s o d r m N n - u a l E c t

4. Dorsal
meso
neuro
epi
dpp
sog
dpp
“sog”
snail

5. dpp versus sog Expression

6. Dpp versus Sog Function
Nucleus
Dorsal or Lateral Region Cell
Inside
Outside
Dpp
Receptor D A
Dorsal Region Cell
Inside
Outside O n f
Repressor
From Mother N
Nucleus
Regulatory Region
Coding Region
Dpp Protein
Signal Relay O n f
Neural genes
(e.g. AS-C) O n f
Non-neural genes
(e.g. dpp)
No Dorsal
dpp mRNA

7. dpp- versus sog- Mutants
Mesodermal Genes
Neuronal Genes
Neuronal Genes
Epidermal Genes X
Dpp
Sog = M e s o d r m N n - u a l E c t

8. dpp- Mutant Sog Neuronal Genes Mesodermal Genes = M e s o d r m N n -c t

9. dpp- Mutant

10. sog- Mutant X Epidermal Genes Dpp Neuronal Genes Sog Neuronal Genes
Mesodermal Genes
Neuronal Genes
Epidermal Genes
Neuronal Genes
Dpp X
Sog = M e s o d r m N n - u a l E c t

11. sog- Mutant Epidermal Genes Dpp Neuronal Genes Mesodermal Genes = M ec t

12. sog- Mutant

13. The Default State of Ectoderm is Neural

14. Sog diffuses and patterns the dorsal region
The Players
Dpp: A signal that promotes dorsal fates
Sog: A secreted inhibitor of Dpp
Tolloid = Tld: A protease that cleaves and destroys Sog

15. Sog diffuses and patterns the dorsal region
Low Dpp
Hi Dpp
Dpp
Tld
Sog
Ventral

16. A Sog protein gradient forms dorsally
Epi A P V D
Neuro
Meso
sog RNA/ Sog Protein

17. Tld limits Sog accumulation dorsallyWT
Df(tld)
Sog protein/dpp RNA

18. 2) A reciprocal Dpp activity gradient forms.
Sog Creates a BMP activity gradient dorsally
[Sog]
Relative DppActivity
Sog
Dpp V D
1) A dorsal Sog gradient is created by a ventral source and a dorsal sink for Sog.
2) A reciprocal Dpp activity gradient forms.

19. Subdivision of the Neuroectoderm
Dorsal
High
Low
None
[Dorsal]
Dpp
Non-neural genes
Neural genes
Neuronal genes
Msh
Ind
Vnd = M e s o d r m N n - u a l E c t

20. Patterning the Neuroectoderm in Flies and Mice
Dorsal
Dpp
ind
msh
vnd
dpp
Drosophila Neuroectoderm
Mouse Neural Tube
Sonic Hh
BMPs
Msx
Nkx2.2
Gsh

21. Ventral Dominant Repression
msh
ind
vnd V

22. Dpp X Dpp signaling represses neural genes in neuroectoderm msh ind
vnd

23. Reciprocal Patterning of the Ectoderm by Sog and Dpp
msh
ind
vnd
Neuroectoderm
Non-neural
Ectoderm
A.S.
race
Relative BMPActivity
[Dpp]
[Sog]
Sog
Dpp V D
1) A Sog gradient creates an inverse Dpp activity gradient dorsally -> Non-neural Ectoderm vs Amnioserosa.
2) A Dpp activity gradient forms within the neuroectoderm -> Three rows of neuroblasts.

24. BMP signaling in the neuroectoderm of flies and vertebrates