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Drosophila dorsal/ventral axis detemination
How are different tissue types specified at
distinct positions on the embryonic dorsalventral axis?
Cell fate specification at the blastoderm stage
amnioserosa
dorsal
dorsal
ectoderm
neuroectoderm
mesoderm
ventral
fate map
mesoderm formation
Dorsal-Ventral fate map
Genes identified in a famous screen for Drosophila
mutants with embryo patterning defects
Torpedo
Gurken
Localized
maternal
mRNA sets
up anterior
and posterior
poles
Gurken protein specifies the Anterior-Posterior
axis of the Drosophila embryo during oogenesis
(Similar to EGF)
Gurken also signals dorsal pole formation during oogenesis
oocyte
nucleus
1-6
A
+
7
8
10A
D
D
-
P
anterior
posterior
V
Gurken
mRNA also
relocalizes
to anterior
dorsal side.
Microtubules
reorient,
nucleus
migrates to
minus end
follicle cells
microtubules
8
V
10A
1-6
+
gurken expression
in the oocyte
gurken expression in the oocyte
Localization of the
Gurken mRNA
and protein
between the
oocyte nucleus
and the dorsal
anterior cell
membrane
Gurken signaling inhibits production of an extracellular
signal (Spätzle) by follicle cells
follicle cells
Torpedo = EGF receptor
(in follicle cells)
Gurken = Epidermal
Growth Factor (EGF)
Oocyte
pipe
expression
X
Ventral follicle
cell
Pipe (Golgi?)
X
Wind (ER?)
Nucleus
X
modified from van Eeden & St.Johnston
Maternal effect mutations in dorso-ventral patterning
Somatic (follicle cells)
nudel, pipe, wbl
ndl, pipe, wbl
dorsal RNA
gd, snk, ea - serine proteases
Spätzle
Toll protein
spz - ligand
Spätzle protein
Germline (nurse cells)
Toll
Dorsal protein
Tl - membrane receptor
Dorsal protein
tube - cytoplasmic protein
pelle - ser/thr protein kinase
cactus
amnio serosa
cact - cytoplasmic inhibitor
dorsal
ectoderm
of Dorsal nuclear
translocation
dorsal
neuroectoderm
dl - transcription factor
(morphogen)
mesoderm
Dl
nuclear protein
dorsal and cactus mutants (maternal germline effect)
dorsal
Wild type
dorsal
cactus
mutant
mutant
A7
A8
A6
A5
A4
A3
A2
T3
A1
T2
T1
ventral
dorsalized
ventralized
Translocation of Dorsal protein into ventral
nuclei but not lateral or dorsal nuclei
Wild type
toll mutant
cactus mutant
Generation of Dorsal-Ventral polarity in Drosophila
Generation of Dorsal-Ventral Polarity in Drosophila
The Toll pathway in dorso-ventral pattern formation
Inject wild-type cytoplasm
into toll mutant eggs
toll mutant
ventral
dorsalized
local
rescue
Wild type
dorsal
ectoderm
dorsal
neuro-ectoderm
(denticle belts)
mesoderm
polarity reversal
Conserved pathway for
regulating nuclear
transport of
transcription factors in
Drosophila and
mammals
Cells with highest nuclear Dorsal levels become mesoderm
Zygotically expressed genes
Action of Dorsal protein in ventral cells
Action of Dorsal protein in ventral cells
High affinity for promoter,
Not much Dorsal needed to activate
Action of Dorsal protein in ventral cells
Lower affinity for promoter,
More Dorsal needed to activate
Zygotically expressed genes
Action of Dorsal protein in ventral cells
Snail repression of rhomboid
creates domains with distinct gene
expression patterns
Dorso-ventral pattern formation: summary
nudel, pipe,
windbeutel
dorsal RNA
Toll protein
Spätzle
protein
Dorsal protein
Dorsal protein
dpp
twist
oocyte nucleus dorsal
> repression of ventral fate
in dorsal follicle cells
ventral production of ligand
> activation of Toll receptor
> graded nuclear uptake
of Dorsal morphogen
> regulation of zygotic
target gene expression
> cell fates along DV axis
Use of a similar regulatory system to pattern insects and vertebrates
Patterns ectoderm in Drosophila
Patterns mesoderm in vertebrates
Gastrulation in Drosophila
Schematic
representation of
gastrulation in
Drosophila