Lecture 5 Anterior Posterior axis formation Cell Biology
Lecture 5 • Anterior Posterior axis formation: Cell Biology • Bicoid is a morphogen
Lab 5 schedule • On Monday and Tuesday come in at the regular time. • On Tuesday and Wednesday come to B&G 3015 to mount your embryos. Elyse will discuss the time of day to come.
Exams • Midterm Tuesday Feb. 28, 2012 UCC 63, 7 -10 PM • Tentative Final exam date Thursday April 19, 2012 at 9: 00 AM
Structure of the egg Dorsal appendage A D P Chorion V Micropyle Vitelline
Cellular Blastoderm Hartenstein 1993
Blastoderm fate map Hartenstein 1993
Simplified Fate Map Nusslein-Volhard et al. , Science 238, 1675 -1681
Classical Embryology Remove 510% of the anterior cytoplasm Remove posterior pole plasm Nusslein-Volhard et al. , Science 238, 1675 -1681
Transplant anterior cytoplasm to posterior Nusslein-Volhard et al. , Science 238, 1675 -1681
Transplant posterior cytoplasm to anterior Nusslein-Volhard et al. , Science 238, 1675 -1681
Transplant posterior cytoplasm to anterior Nusslein-Volhard et al. , Science 238, 1675 -1681
Transplant posterior cytoplasm to an anterior that lacks the anterior signal Nusslein-Volhard et al. , Science 238, 1675 -1681
Properties of the polar center signals • Both exert long range effects • The anterior and posterior activities inhibit each other • Both activities have inductive properties
Properties of the polar center signals • Both exert long range effects
Classical Embryology Remove 510% of the anterior cytoplasm Remove posterior pole plasm Nusslein-Volhard et al. , Science 238, 1675 -1681
Properties of the polar center signals • The anterior and posterior activities inhibit each other
Transplant posterior cytoplasm to anterior Nusslein-Volhard et al. , Science 238, 1675 -1681
Transplant anterior cytoplasm to posterior Nusslein-Volhard et al. , Science 238, 1675 -1681
Properties of the polar center signals • Both activities have inductive properties
Transplant anterior cytoplasm to posterior Nusslein-Volhard et al. , Science 238, 1675 -1681
Transplant posterior cytoplasm to an anterior that lacks the anterior signal Nusslein-Volhard et al. , Science 238, 1675 -1681
What you may know already Bicoid: Anterior signal Nanos: Posterior signal How do we know this?
Maternal effect screens Normal egg bcd/bcd mother Larva missing a head
Nusslein-Volhard et al. , Science 238, 1675 -1681
Three classes of maternal effect phenotypes Nusslein-Volhard et al. , Science 238, 1675 -1681
The real cuticles wt bcd oskar torso Nusslein-Volhard et al. , Science 238, 1675 -1681
Mutant combinations St Johnston and Nusslein-Volhard Cell 1992
Transplantation of cytoplasm into bcd mutants Nusslein-Volhard et al. , Science 238, 1675 -1681
Controlling anterior posterior polarity Nusslein-Volhard et al. , Science 238, 1675 -1681
The difference between the posterior and anterior signals Nusslein-Volhard et al. , Science 238, 1675 -1681
Distinct Properties of the signals • Anterior signal-instructive. Induces polarity at site of injection. • Posterior signal-permissive. Polarity independent of injection site.
Evidence for Bicoid • Rescue activity spatially distributed • Amount of rescue dependent on amount injected • Linear relationship between gene dose and rescue activity • m. RNA asymmetrically localized and protein expressed in a gradient
Bicoid rescue assay Nusslein-Volhard et al. , Science 238, 1675 -1681
Rescue activity is spatially distributed 100% % rescue activity 50% 100% 40% % egg length 0%
Amount of rescue is dependent on amount injected 100% % rescue activity 50% 0 1/3 2/3 Transplanted volume 1
Linear relationship between gene dose and rescue activity 100% % rescue activity 50% 0 1 2 3 Dose of bicoid gene in mothers
m. RNA assymetrically localized and protein expressed in a gradient m. RNA Protein Driever and Nusslein-Volhard Cell 54, 83 -93
Bicoid • Bicoid has the properties of the anterior signal • Does Bicoid need to interact with any other anteriorly localized signals to work?
Bicoid is necessary and sufficient Bicoid m. RNA made in vitro m. RNA injected at posterior pole Bicoid protein expression Larva with two heads Driever et al. , 1990 Development 109, 811 -820
Bicoid • Bicoid is the anterior signal • What does Bicoid encode? • How does Bicoid work?
Bicoid encodes a homeodomain containing protein.
Hunchback lacks anterior segments Nusslein-Volhard and Wieschaus 1980 Nature 287, 795
Hunchback is expressed at the anterior pole Bicoid m. RNA Bicoid protein Hunchback m. RNA expression Driever 1993
Hunchback gene Driever and Nusslein-Volhard Nature 337, 138 -143
Bicoid is a transcriptional activator Driever and Nusslein-Volhard Nature 337, 138 -143
m. RNA assymetrically localized and protein expressed in a gradient m. RNA Protein Driever and Nusslein-Volhard Cell 54, 83 -93
Morphogen • Long range action • Affect polarity • Concentration dependent • Different fates at different concentrations
Morphogen • Long range action
Hunchback is expressed at the anterior pole Bicoid m. RNA Bicoid protein Hunchback m. RNA expression Driever 1993
Morphogen • Affect polarity
Bicoid is necessary and sufficient Bicoid m. RNA made in vitro m. RNA injected at posterior pole Bicoid protein expression Larva with two heads Driever et al. , 1990 Development 109, 811 -820
Morphogen • Concentration dependent
Concentration dependence of Bicoid function
Concentration dependence of Bicoid function # of bicoid genes in the mother hb-lac. Z expression 0 1 2 4 6 Struhl et al. , 1989 Cell 57, 1259 -1273
Morphogen • Different fates at different concentrations
Distinct Bicoid binding sites are activated at different concentrations of Bicoid
Morphogen • Long range action • Affect polarity • Concentration dependent • Different fates at different concentrations
How is bicoid m. RNA localized to the anterior pole?
Other anterior class mutants Driever and Nusslein-Volhard Cell 54, 94 -104
Bicoid gradient affected in the mutants Driever and Nusslein-Volhard Cell 54, 94 -104
The mutants affect different stages of bicoid m. RNA deposition in the developing oocyte St. Johnston et al. , 1989 Development sup 13 -19
Localization of bicoid m. RNA: recent paper Irion and St Johnston 2007 Nature 445, 554 -558
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