Evolution of segmentation: mRNA localization

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Les Treilles 2
Evolution of segmentation mRNA localization
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Drosophila segmentation hierarchy
Maternal coordinate
Gap
Pair-rule
Segment polarity
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(No Transcript)
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The Bicoid morphogenetic gradient
Instructive function Activation of anterior
genes Permissive function Repression of
posterior identity
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Bicoid differentially activates anterior genes
bcd
Bcd
head
thorax
abdomen
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Bicoid represses caudal translation

cad
bcd
Cad
Bcd
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Regulation of maternal Hunchback mRNA
hb
nos
Hb
Nos
Nos
Hb
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Non-conserved
Conserved
Caudal
Bicoid
Nanos
Hunchback
otd
cad
ot
d
Kr
hb
Head
Thorax
Abdomen
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BcdHb
Drosophila
otd
ems
btd
hb
Head
thoracic
abdominal
Gnathal
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Tribolium Otd
Tc otd
Nos
R. Schröder, 2003
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(No Transcript)
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Insect Relationships
bcd
Long germ
Drosophila
Anopheles (mosquito)
Tribolium (beetle)
Nasonia
Apis (honeybee)
Schistocerca (locust)
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Wasp Nasonia vitripennis

• - Parasitoid of large fly pupae
• - Haplo-diploid genetics
• - Long germband embryogenesis

Drosophila
Nasonia
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BcdHb
Drosophila
otd
ems
btd
hb
Head
thoracic
abdominal
Gnathal
Otd?
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(No Transcript)
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Nasonia otd1 ovary localization
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Parental RNAi in Nasonia
Inject female pupae with dsRNA
Injected pupae eclose and lay eggs
Examine resulting larvae for cuticle defects
Slp RNAi
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otd1 RNAi cuticle phenotypes
wt
A1
A2
A3
T2
Anterior headless thoracic defects Posterior
6 ab segments missing
A2
A1
A3
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otd acts as a morphogen
otd1 RNAi
wt
ems
gt
hb
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BcdHb
Drosophila
otd
ems
btd
hb
Head
thoracic
abdominal
Gnathal
Otd
Cad?
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Bicoid regulates caudal translation in Drosophila
Who localizes caudal in Nasonia?
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(No Transcript)
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Gap genes in Nasonia
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giant is expressed maternally
and is localized!
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giant controls hb, but not otd
otd
hb
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giant represses Kr
Kr represses hb
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giant represses Kr, which represses hb Kr RNAi
rescues gt RNAi!
gt mat
hbzyg
Kr
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Nasonia uses mRNA localization
Nvit cad
Nvit nos
Nvit otd
Nvit gt
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Short germband posterior morphogenetic center
Otd
Hb
Nos
Ant. head
Gnathal
thorax
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A second morphogenetic center allows long
germband development
Heterochronic shift of posterior genes from
germband to blastoderm stage
Ant. Head
Gnathal
thorax
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In flies, Bcd is the anterior morphogen Who acts
at the posterior?
Hb
Tll? (Torso)
Bcd
Ant. Head
Terminal
Post. abd
Gnathal
thorax
abdomen
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Jeremy Lynch Eugenia Olesnicky Ava Brent
Miriam Rosenberg
Mary Anne Pultz Jack Werren
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Polyembryonic wasp Copidosoma
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Drosophila
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Redundancy between hbmat and bcd-dependent hbzyg



Bicoid
zyg
hb
Nan
os
mat
t
hb
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Ancestral anterior patterning molecules
hunchback - Conserved - Bicoid Synergy -
Thoracic rescue
orthodenticle (otd) - Conserved anterior - K50 HD
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Otd protein gradient
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Conserved
Hunchback
Bicoid
cad
ot
d
Kr
hb
Head
Thorax
Abdomen
E. Wimmer, D. Tautz G. Struhl
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Is the Bicoid gradient required?
BcdHb
otd
ems
btd
hb
Gnathal
Ant Head
Thoracic
Abdominal
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Bcd Hb
Bcd
otd
ems
btd
hb
Gnathal
Ant Head
Thoracic
Abdominal
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The Bicoid gradient can be by-passed!!
Bic
oi
d
m
at
4X

h
b
Hunchback
Bic
oi
d
He
a
d

He
a
d

Tho
ra
x

Ab
do
m
en

Tho
ra
x

Ab
do
m
en

- Remove
2X
bcd
- Replace
with 4X
F
LAT
bcd
- Remove matzyg
hb

(Germline clones)
- Replace with
4X
hb
P1
only
- Remove
hb

knirps
i
n males
- Add 2X
hb
P1
only in males

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The Bicoid gradient can be by-passed!!
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Evolution of Bcd
short germband insect

Extra-embryonic
A
P
embryo
A
Hox(Q50)
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2
3
4
Drosophila

zen
Amnioserosa
Otd
(Q50)
Cad