d v high [dorsal] low [dorsal] no dorsal graded dorsal concentration created by mother hierarchy of...

24

Post on 19-Dec-2015

238 views

Category:

Documents


1 download

TRANSCRIPT

D

V

High [Dorsal]

Low [Dorsal]

No Dorsal

Graded Dorsal Concentration

Created by Mother

Hierarchy of Gene Action in D/V Patterning

Mesoderm Genes

Neuroectoderm Genes

Non-neural Genes

D/V Genes Basic Tissue Types

Controlled by Embryo

= Mesoderm = Non-Neural Ectoderm= Neuroectoderm

Epidermal GenesDpp Neuronal Genes

AS-C

Rho Ventral Epidermal Genes

Neural Genes

Twist Mesodermal GenesSnail Neural Genes

Brk, Sog Dorsal Genes

Dorsal

meso

neuroneuro

epi

snail

dpp

“sog” sog

dpp

dpp versus sog Expression

sog

dpp

D A

Dorsal Region Cell

Inside

Outside

OnOff

RepressorFrom Mother

N

Nucleus

Regulatory Region

Coding Region

Nucleus

Dorsal or Lateral Region Cell

Inside

Outside

DppReceptor

Sog

Signal Relay

OnOff

Non-neural genes(e.g. dpp)

OnOff

Neural genes(e.g. AS-C)

dpp mRNA

No Dorsal

Dpp Protein

Dpp versus Sog Function

Mesodermal Genes

Neuronal Genes

= Mesoderm = Non-Neural Ectoderm= Neuroectoderm

Dpp

Sog

dpp- versus sog- Mutants

X Neuronal GenesEpidermal Genes

Mesodermal Genes

= Mesoderm = Non-Neural Ectoderm= Neuroectoderm

dpp- Mutant

Neuronal GenesSog

dpp- Mutant

Mesodermal Genes

Neuronal Genes

= Mesoderm = Non-Neural Ectoderm= Neuroectoderm

Dpp

Sog

sog- Mutant

X

Neuronal GenesEpidermal Genes

Mesodermal Genes

= Mesoderm = Non-Neural Ectoderm= Neuroectoderm

Dpp Neuronal GenesEpidermal Genes

sog- Mutant

sog- Mutant

The Default State of Ectoderm is Neural

N o n -n e u r a l

E c t o d e r m

N e u r o e c t o d e r m

( D e f a u l t S t a t e )

SogBlocks Dpp Autoactivation

Permits Neurogenesis

NeurogenesisDpp

Autoactivates

Skin

Subdivision of the Ectoderm intoNeural Versus Non-neural Regions

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

Dorsal

Ventral

Tld Low Dpp

Hi DppDpp

Sog

Sog diffuses and patterns the dorsal region

A Sog protein gradient forms dorsally

Epi

Neuro

Meso

A P

V

D

sog RNA/ Sog Protein

Sog protein/dpp RNA

Tld limits Sog accumulation dorsally

WT Df(tld)

Sog Creates a BMP activity gradient dorsally

Sog Dpp

V D

Relative DppActivity

[Sog]

1) A dorsal Sog gradient is created by a ventral source and a dorsal sink for Sog.

2) A reciprocal Dpp activity gradient forms.

= Mesoderm = Non-Neural Ectoderm= Neuroectoderm

High

Low

None

[Dorsal]

High

Low

None

DppNon-neural genes

Neural genes

Dorsal

Subdivision of the Neuroectoderm

Neuronal genes

Msh

Ind

Vnd

Drosophila Neuroectoderm

Mouse Neural Tube

Sonic Hh

BMPsMsx Nkx2.2Gsh

Dorsal

Dpp

indmsh

vnd

dpp

Patterning the Neuroectoderm in Flies and Mice

ind

vnd

msh

D

V

Ventral Dominant Repression

vnd

Dpp

Dpp signaling represses neural genes in neuroectoderm

msh

indX

Reciprocal Patterning of the Ectoderm by Sog and Dpp

Sog Dpp

V D

[Sog]

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.

[Dpp]

Relative BMPActivity

mshindvndNeuroectoderm Non-neural

EctodermA.S.race

BMP signaling in the neuroectoderm of flies and vertebrates

M s x

N k x - 2

B M P - 4

C h d

( = F lo o rp la t e )

V e n t ra l M id lin e

Drosophila Neuroectoderm Vertebrate Neural Plate

m s h

v n d

V e n t r a l

M i d l i n e

d p p

S o g G s hi n d