Drosophila dorsal ventral axis detemination
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Drosophila dorsal/ventral axis detemination. How are different tissue types specified at distinct positions on the embryonic dorsal-ventral axis?. Cell fate specification at the blastoderm stage. amnio-serosa. dorsal. dorsal ectoderm. neuro-ectoderm. mesoderm. ventral. fate map.

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Drosophila dorsal/ventral axis detemination

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Drosophila dorsal ventral axis detemination
Drosophila dorsal/ventral axis detemination

How are different tissue types specified at distinct positions on the embryonic dorsal-ventral axis?


Drosophila dorsal ventral axis detemination

Cell fate specification at the blastoderm stage

amnio-serosa

dorsal

dorsal ectoderm

neuro-ectoderm

mesoderm

ventral

fate map

mesoderm formation



Drosophila dorsal ventral axis detemination

Genes identified in a famous screen for Drosophila mutants with embryo patterning defects

Torpedo

Gurken



Gurken protein specifies the anterior posterior axis of the drosophila embryo during oogenesis
Gurken protein specifies the Anterior-Posterior axis of the Drosophila embryo during oogenesis

(Similar to EGF)


Gurken also signals dorsal pole formation during oogenesis

migration of nucleus Drosophila embryo during oogenesis

10A

8

1-6

-

+

-

gurken expression in the oocyte

gurken expression in the oocyte

Gurken also signals dorsal pole formation during oogenesis

oocyte nucleus

D

D

10A

1-6

7

8

+

-

A

P

-

V

anterior

posterior

V

follicle cells

microtubules


Drosophila dorsal ventral axis detemination
Expression of the Drosophila embryo during oogenesisGurken Message and Protein Between the Oocyte Nucleus and the Dorsal Anterior Cell Membrane


Gurken signaling inhibits production of an extracellular signal sp tzle by follicle cells
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?)

X

Nucleus

modified from van Eeden & St.Johnston


Drosophila dorsal ventral axis detemination

Maternal effect mutations in dorso-ventral patterning signal (Sp

Somatic (follicle cells)

ndl, pipe, wbl

gd, snk, ea - serine proteases

Spätzle spz - ligand

Germline (nurse cells)

nudel, pipe, wbl

dorsal RNA

Toll protein

Spätzle protein

Dorsal protein

Toll

Tl - membrane receptor

tube - cytoplasmic protein

pelle - ser/thr protein kinase

Dorsal protein

amnio serosa

cact - cytoplasmic inhibitor of Dorsal nuclear translocation

cactus

dorsal ectoderm

neuro-ectoderm

dorsal

dl - transcription factor (morphogen)

mesoderm

Dl

nuclear protein


Drosophila dorsal ventral axis detemination

dorsal signal (Sp and cactus mutants (maternal germline effect)

dorsal

dorsal mutant

cactus mutant

Wild type

ventral

A8

T1

A7

dorsalized

ventralized

T2

T3

A1

A2

A6

A3

A4

A5


Translocation of dorsal protein into ventral nuclei but not lateral or dorsal nuclei
Translocation of Dorsal protein into ventral nuclei but not lateral or dorsal nuclei

Wild type toll mutant cactus mutant




Drosophila dorsal ventral axis detemination

The Toll pathway in dorso-ventral pattern formation lateral or dorsal nuclei

Inject wild-type cytoplasm

into toll mutant eggs

toll mutant

ventral

dorsalized

local

rescue

dorsal ectoderm

Wild type

dorsal

neuro-ectoderm

(denticle belts)

mesoderm

polarity reversal


Drosophila dorsal ventral axis detemination
Conserved pathway for regulating nuclear transport of transcription factors in Drosophila and mammals


Drosophila dorsal ventral axis detemination

Cells with highest nuclear Dorsal levels become mesoderm transcription factors in Drosophila and mammals


Drosophila dorsal ventral axis detemination

Zygotically transcription factors in Drosophila and mammals expressed genes


Drosophila dorsal ventral axis detemination

Action of Dorsal protein in ventral cells transcription factors in Drosophila and mammals


Drosophila dorsal ventral axis detemination

Action of Dorsal protein in ventral cells transcription factors in Drosophila and mammals

High affinity for promoter,

Not much Dorsal needed to activate


Drosophila dorsal ventral axis detemination

Action of Dorsal protein in ventral cells transcription factors in Drosophila and mammals

Lower affinity for promoter,

More Dorsal needed to activate


Drosophila dorsal ventral axis detemination

Zygotically transcription factors in Drosophila and mammals expressed genes


Drosophila dorsal ventral axis detemination

Action of Dorsal protein in ventral cells transcription factors in Drosophila and mammals

Snail repression of rhomboid creates domains with distinct gene expression patterns


Drosophila dorsal ventral axis detemination

Dorso-ventral pattern formation: summary transcription factors in Drosophila and mammals

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



Drosophila dorsal ventral axis detemination

Patterns ectoderm in Drosophila vertebrates

Patterns mesoderm in vertebrates





Drosophila dorsal ventral axis detemination

3 head vertebrates

The fly body plan: each segment has a unique identity

and produces distinctive

structures

3 thorax

8 abdomen


Drosophila dorsal ventral axis detemination

Mutations affecting the antero-posterior axis vertebrates

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




Drosophila dorsal ventral axis detemination

bicoid vertebrates mutant phenotype

Embryo from wild-type mother

Embryo from bicoid mother


Drosophila dorsal ventral axis detemination

Anterior: bicoid is required for head and thorax vertebrates

bicoid mutant

Wild type

blastoderm fate map

head

abdomen

+ thorax

abdomen


Drosophila dorsal ventral axis detemination

Bicoid vertebrates mRNA localization in embryo

(tethered to microtubules)


Nuclei divide without cell division in drosophila to produce a syncytial blastoderm embryo
Nuclei divide without cell division in vertebratesDrosophila to produce a syncytial blastoderm embryo

Fig. 9.1


Drosophila dorsal ventral axis detemination

Bicoid protein gradient in syncytial blastoderm embryo vertebrates

- diffuses after translation from localized mRNA

- protein unstable


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