Anterior%20Posterior%20axis%20formation:%20Cell%20Biology

1
Lecture 5

• Anterior Posterior axis formation Cell Biology
• Bicoid is a morphogen

2
Lab 5 schedule

• On Monday and Tuesday come in at the regular
  time.
• On Tuesday and Wednesday come to BG 3015 to
  mount your embryos. Elyse will discuss the time
  of day to come.

3
Exams

• Midterm Tuesday Feb. 28, 2012
• UCC 63, 7-10PM
• Tentative Final exam date Thursday April 19, 2012
  at 900AM

4
Structure of the egg
Dorsal appendage
D
Chorion
A
P
V
Micropyle
Vitelline
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Cellular Blastoderm
Hartenstein 1993
6
Blastoderm fate map
Hartenstein 1993
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Simplified Fate Map
Nusslein-Volhard et al., Science 238, 1675-1681
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Classical Embryology
Remove 5-10 of the anterior cytoplasm
Remove posterior pole plasm
Nusslein-Volhard et al., Science 238, 1675-1681
9
Transplant anterior cytoplasm to posterior
Nusslein-Volhard et al., Science 238, 1675-1681
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Transplant posterior cytoplasm to anterior
Nusslein-Volhard et al., Science 238, 1675-1681
11
Transplant posterior cytoplasm to anterior
Nusslein-Volhard et al., Science 238, 1675-1681
12
Transplant posterior cytoplasm to an anterior
that lacks the anterior signal
Nusslein-Volhard et al., Science 238, 1675-1681
13
Properties of the polar center signals

• Both exert long range effects
• The anterior and posterior activities inhibit
  each other
• Both activities have inductive properties

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Properties of the polar center signals

• Both exert long range effects

15
Classical Embryology
Remove 5-10 of the anterior cytoplasm
Remove posterior pole plasm
Nusslein-Volhard et al., Science 238, 1675-1681
16
Properties of the polar center signals

• The anterior and posterior activities inhibit
  each other

17
Transplant posterior cytoplasm to anterior
Nusslein-Volhard et al., Science 238, 1675-1681
18
Transplant anterior cytoplasm to posterior
Nusslein-Volhard et al., Science 238, 1675-1681
19
Properties of the polar center signals

• Both activities have inductive properties

20
Transplant anterior cytoplasm to posterior
Nusslein-Volhard et al., Science 238, 1675-1681
21
Transplant posterior cytoplasm to an anterior
that lacks the anterior signal
Nusslein-Volhard et al., Science 238, 1675-1681
22
What you may know already
Bicoid Anterior signal Nanos Posterior signal
How do we know this?
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Maternal effect screens
Normal egg
bcd/bcd mother
Larva missing a head
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Nusslein-Volhard et al., Science 238, 1675-1681
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Three classes of maternal effect phenotypes
Nusslein-Volhard et al., Science 238, 1675-1681
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The real cuticles
wt bcd oskar torso
Nusslein-Volhard et al., Science 238, 1675-1681
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Mutant combinations
St Johnston and Nusslein-Volhard Cell 1992
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Transplantation of cytoplasm into bcd mutants
Nusslein-Volhard et al., Science 238, 1675-1681
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Controlling anterior posterior polarity
Nusslein-Volhard et al., Science 238, 1675-1681
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The difference between the posterior and anterior
signals
Nusslein-Volhard et al., Science 238, 1675-1681
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Distinct Properties of the signals

• Anterior signal-instructive. Induces polarity at
  site of injection.
• Posterior signal-permissive. Polarity
  independent of injection site.

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Evidence for Bicoid

• Rescue activity spatially distributed
• Amount of rescue dependent on amount injected
• Linear relationship between gene dose and rescue
  activity
• mRNA asymmetrically localized and protein
  expressed in a gradient

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Bicoid rescue assay
Nusslein-Volhard et al., Science 238, 1675-1681
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Rescue activity is spatially distributed
100
rescue activity
50
100
0
40
egg length
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Amount of rescue is dependent on amount injected
100
rescue activity
50
0
1/3
2/3
1
Transplanted volume
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Linear relationship between gene dose and rescue
activity
100
rescue activity
50
3
0
1
2
Dose of bicoid gene in mothers
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(No Transcript)
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mRNA assymetrically localized and protein
expressed in a gradient
mRNA
Protein
Driever and Nusslein-Volhard Cell 54, 83-93
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Bicoid

• Bicoid has the properties of the anterior signal
• Does Bicoid need to interact with any other
  anteriorly localized signals to work?

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(No Transcript)
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Bicoid is necessary and sufficient
Bicoid mRNA made in vitro
mRNA injected at posterior pole
Bicoid protein expression
Larva with two heads
Driever et al., 1990 Development 109, 811-820
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Bicoid

• Bicoid is the anterior signal
• What does Bicoid encode?
• How does Bicoid work?

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Bicoid encodes a homeodomain containing protein.
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Hunchback lacks anterior segments
Nusslein-Volhard and Wieschaus 1980 Nature 287,
795
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Hunchback is expressed at the anterior pole
Bicoid mRNA
Bicoid protein
Hunchback mRNA expression
Driever 1993
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Hunchback gene
Driever and Nusslein-Volhard Nature 337, 138-143
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Bicoid is a transcriptional activator
Driever and Nusslein-Volhard Nature 337, 138-143
48
mRNA assymetrically localized and protein
expressed in a gradient
mRNA
Protein
Driever and Nusslein-Volhard Cell 54, 83-93
49
Morphogen

• Long range action
• Affect polarity
• Concentration dependent
• Different fates at different concentrations

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Morphogen

• Long range action

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Hunchback is expressed at the anterior pole
Bicoid mRNA
Bicoid protein
Hunchback mRNA expression
Driever 1993
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Morphogen

• Affect polarity

53
Bicoid is necessary and sufficient
Bicoid mRNA made in vitro
mRNA injected at posterior pole
Bicoid protein expression
Larva with two heads
Driever et al., 1990 Development 109, 811-820
54
Morphogen

• Concentration dependent

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Concentration dependence of Bicoid function
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Concentration dependence of Bicoid function
hb-lacZ expression
of bicoid genes in the mother
0
1
2
4
6
Struhl et al., 1989 Cell 57, 1259-1273
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Morphogen

• Different fates at different concentrations

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Distinct Bicoid binding sites are activated at
different concentrations of Bicoid
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(No Transcript)
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Morphogen

• Long range action
• Affect polarity
• Concentration dependent
• Different fates at different concentrations

61
How is bicoid mRNA localized to the anterior pole?
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(No Transcript)
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Other anterior class mutants
Driever and Nusslein-Volhard Cell 54, 94-104
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Bicoid gradient affected in the mutants
Driever and Nusslein-Volhard Cell 54, 94-104
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The mutants affect different stages of bicoid
mRNA deposition in the developing oocyte
St. Johnston et al., 1989 Development sup 13-19
66
Localization of bicoid mRNA recent paper
Irion and St Johnston 2007 Nature 445, 554-558