1. 1 time * transcription factors expressed in large blocks
Developmental biology:
segment polarity genes and cell signalling b i c o d g a p e n s
time
* transcription factors expressed in large blocks
* induce expression of downstream transcription factors in smaller blocks
* generates segmental expression (14) of segment polarity genes.
February 06 1

2. 2 Non-cellular: syncitium
Developmental biology:
segment polarity genes and cell signalling
Non-cellular:
syncitium
Transcription factors are able to determine more than
just the nuclei that produce them
February 06 2

3. 3 How do you relate the molecular expression of
Developmental biology:
segment polarity genes and cell signalling
How do you relate the molecular expression of
segment polarity genes in stripes in cells in every
segment, to the final larval structure….?
February 06 3

4. 4 Each segment is affected in a wingless mutant:
Developmental biology:
segment polarity genes and cell signalling
normal
wingless
mutant
Each segment is affected in a
wingless mutant:
cells making “naked” cuticle
are mis-patterned and are lost
(death) or redirected to form
denticles
February 06 4

5. 5 * mutants: each segment polarity mutant shows
Developmental biology:
segment polarity genes and cell signalling
* mutants: each segment polarity mutant shows
identical defect repeated in every segment
* conclusion: segment polarity proteins are
required for pattern formation in each and every segment
* different classes: role?
February 06 5

6. 6 * detailed analysis of expression.
Developmental biology:
segment polarity genes and cell signalling
* detailed analysis of expression.
* wingless expressed in one cell wide
stripe
February 06 6

7. 7 * wingless gene encodes for a secreted signalling protein;
Developmental biology:
segment polarity genes and cell signalling
expression of wingless gene
* wingless gene encodes for a secreted signalling protein;
Int-1 (now Wnt-1) gene cloned in mice as being involved in breast cancer
* Secreted molecules being involved in patterning
consistent with fact that embryo is now cellularised!
February 06 7

8. Developmental biology:
segment polarity genes and cell signalling
* how do segment polarity genes generate pattern? Targets of signalling?
engrailed expression in
normal embryo
engrailed expression in
wingless mutant embryo
wingless
engrailed
* wingless acts on neighbouring cells to
maintain engrailed expression.
February 06 8

9. 9 * hedgehog gene encodes for a secreted signalling protein.
Developmental biology:
segment polarity genes and cell signalling
* wingless acts on neighbouring cells to
maintain engrailed expression.
* hedgehog gene encodes
for a secreted signalling
protein.
wingless
hedgehog
* wingless also acts to maintain expression of
hedgehog gene in neighbouring cells
* target of hedgehog
signalling?
February 06 9

10. Developmental biology:
segment polarity genes and cell signalling
wingless expression
in normal embryo
wingless expression in
hedgehog mutant embryo
wingless
hedgehog
* two signalling molecules maintain each others expression:
maintain a stable reference point in segment
February 06 10

11. 11 hedgehog wingless ? How does the “boundary” get there….
Developmental biology:
segment polarity genes and cell signalling
hedgehog
wingless
? How does the “boundary” get there….
Pair rule gene activity
Anterior precise’sh (posterior not);
Segment polarity interplay refines
expression domains and sets up
segment boundaries (later, see textbooks).
February 06 11

12. Developmental biology:
segment polarity genes and cell signalling
Stability?
Field of cells: virgin area where no/little prepatterning has taken
place. What is the most efficient way of turning this into
something useful for the animal?
* simple (as little genes/protein as possible)
* reliable
* accident resistant
February 06 12

13. secreted signal: efficient!? Damage: ie loss of blue cell
Developmental biology:
segment polarity genes and cell signalling
Damage:
ie loss of blue cell
is devastating….
growth
secreted signal:
efficient!?
Blue cell has to be fixed
to stay blue
Not all daughters can stay blue
February 06 13

14. identity is actively kept
Developmental biology:
segment polarity genes and cell signalling
* blue and green cell
identity is actively kept
growth
* loss of one blue cell is
corrected
* regeneration….
February 06 14

15. * regeneration…. 15 flatworms amphibians
Developmental biology:
segment polarity genes and cell signalling
amphibians
* regeneration….
flatworms
Molecules that drive regeneration important for stem cell technology
February 06 15

16. 16 * genetic studies to unravel segment patterning:
Developmental biology:
segment polarity genes and cell signalling
* genetic studies to unravel segment patterning:
wingless
hedgehog
identical phenotype:
molecules work to common end
wingless expression in smo-/-
Smo
Hedgehog protein X
February 06 16

17. 17 * patched mutant phenotype is very different from
Developmental biology:
segment polarity genes and cell signalling
patched
normal
* patched mutant phenotype is very different from
hedgehog or wingless mutant phenotype
wingless
hedgehog
* what does this mean “molecularly”?
February 06 17

18. 18 * overexpression of hedgehog using a transgene, leads to same
Developmental biology:
segment polarity genes and cell signalling
normal
patched
mutant
overexpression
of hedgehog gene
* overexpression of hedgehog using
a transgene, leads to same
phenotype as patched mutant
patched
= hedgehog everywhere
patched
mutant
February 06 18

19. 19 patched-hedgehog double mutant patched mutant =
Developmental biology:
segment polarity genes and cell signalling
patched-hedgehog
double mutant
patched mutant =
hedgehog over-expression
hedgehog
patched hedgehog
normal
patched
mutant
* patched hedgehog double mutant:
looks like patched single mutant.
hedgehog patched signalling
downstream
February 06 19

20. 20 patched-hedgehog double mutant
Developmental biology:
segment polarity genes and cell signalling
patched-hedgehog double mutant
* patched gene expression in all cells that
do not express hedgehog gene.
* patched required downstream of hedgehog: inhibits signalling
hedgehog patched signalling
downstream
* patched gene encodes for twelve transmembrane protein.
* patched protein can bind hedgehog protein
February 06 20

21. 21 hedgehog Smo Ptc Fu Su(fu) Cos2 Ci Ci Developmental biology:
segment polarity genes and cell signalling
Ptc
hedgehog
Smo
Cos2 Fu
Su(fu) Ci Ci
February 06 21

22. 26 hedgehog protein processing: proteolytic activity
Developmental biology:
segment polarity genes and cell signalling
hedgehog protein processing:
proteolytic activity
cholesterol addition
acyltransferase
* patched protein contains sterol sensing domain
February 06 26

23. 22 http://www.stanford.edu/~rnusse/wntwindow.html
Developmental biology:
segment polarity genes and cell signalling
February 06 22

24. 23 * two secreted signals (hedgehog and wingless) that
Developmental biology:
segment polarity genes and cell signalling
* two secreted signals (hedgehog and wingless) that
are required to pattern each segment.
* other segment polarity genes encode for proteins
that act either in hedgehog or wingless pathway.
wingless
hedgehog
* fine patterning of segment: late roles for wingless
and hedgehog.
February 06 23

25. 24 * patterning via signalling proteins is most common way of
Developmental biology:
segment polarity genes and cell signalling
wingless
hedgehog
* patterning via signalling proteins is most common way of
development (cellular mode of development).
* signalling processes conserved? YES!
* wingless is fly homologue of a vertebrate oncogene: Wnt-1
* patterning molecules are heading a differentiation/growth
decision pathway!
February 06 24

26. 29 Roles for segment polarity proteins in other animals?
Developmental biology:
segment polarity genes and cell signalling
Roles for segment polarity proteins in other animals?
in development: midline (ventral Hedgehog; dorsal wnt)
In patterning of arms/legs
In cell differentiation (neurons, germline cells, “organs”)
In control of cell growth (skin, mammary gland)
Ageing?
February 06 29