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, 7-10PM Tentative Final exam date Thursday April 19, 2012 at 9:00AM

Structure of the egg Dorsal appendage Chorion Vitelline Micropyle D V A P

Cellular Blastoderm Hartenstein 1993

Blastoderm fate map Hartenstein 1993

Simplified Fate Map Nusslein-Volhard et al., Science 238,

Remove posterior pole plasm Classical Embryology Remove 5- 10% of the anterior cytoplasm Nusslein-Volhard et al., Science 238,

Transplant anterior cytoplasm to posterior Nusslein-Volhard et al., Science 238,

Transplant posterior cytoplasm to anterior Nusslein-Volhard et al., Science 238,

Transplant posterior cytoplasm to anterior Nusslein-Volhard et al., Science 238,

Transplant posterior cytoplasm to an anterior that lacks the anterior signal Nusslein-Volhard et al., Science 238,

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

Remove posterior pole plasm Classical Embryology Remove 5- 10% of the anterior cytoplasm Nusslein-Volhard et al., Science 238,

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,

Transplant anterior cytoplasm to posterior Nusslein-Volhard et al., Science 238,

Properties of the polar center signals Both activities have inductive properties

Transplant anterior cytoplasm to posterior Nusslein-Volhard et al., Science 238,

Transplant posterior cytoplasm to an anterior that lacks the anterior signal Nusslein-Volhard et al., Science 238,

What you may know already Bicoid: Anterior signal Nanos: Posterior signal How do we know this?

Maternal effect screens bcd/bcd mother Normal egg Larva missing a head

Nusslein-Volhard et al., Science 238,

Three classes of maternal effect phenotypes Nusslein-Volhard et al., Science 238,

The real cuticles wt bcd oskar torso Nusslein-Volhard et al., Science 238,

Mutant combinations St Johnston and Nusslein-Volhard Cell 1992

Transplantation of cytoplasm into bcd mutants Nusslein-Volhard et al., Science 238,

Controlling anterior posterior polarity Nusslein-Volhard et al., Science 238,

The difference between the posterior and anterior signals Nusslein-Volhard et al., Science 238,

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 mRNA asymmetrically localized and protein expressed in a gradient

Bicoid rescue assay Nusslein-Volhard et al., Science 238,

% rescue activity 100% 50% % egg length 100% 0%40% Rescue activity is spatially distributed

% rescue activity 01/32/31 Amount of rescue is dependent on amount injected 100% 50% Transplanted volume

Linear relationship between gene dose and rescue activity 100% 50% % rescue activity Dose of bicoid gene in mothers

mRNA assymetrically localized and protein expressed in a gradient mRNA 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 mRNA made in vitro mRNA injected at posterior pole Bicoid protein expression Larva with two heads Driever et al., 1990 Development 109,

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

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

Hunchback gene Driever and Nusslein-Volhard Nature 337,

Bicoid is a transcriptional activator Driever and Nusslein-Volhard Nature 337,

mRNA assymetrically localized and protein expressed in a gradient mRNA 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

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

Morphogen Affect polarity

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,

Morphogen Concentration dependent

Concentration dependence of Bicoid function

# of bicoid genes in the mother hb-lacZ expression Concentration dependence of Bicoid function Struhl et al., 1989 Cell 57,

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 mRNA localized to the anterior pole?

Other anterior class mutants Driever and Nusslein-Volhard Cell 54,

Bicoid gradient affected in the mutants Driever and Nusslein-Volhard Cell 54,

The mutants affect different stages of bicoid mRNA deposition in the developing oocyte St. Johnston et al., 1989 Development sup 13-19

Localization of bicoid mRNA: recent paper Irion and St Johnston 2007 Nature 445,