Anterior-posterior patterning in Drosophila

The fly body plan: Each segment has a unique identity 3 head The fly body plan: Each segment has a unique identity and produces distinct structures 3 thorax 8 abdomen

Figures\Chapter09\DevBio7e09053.jpg

Mutations affecting the antero-posterior axis 3 independent maternal systems: anterior, posterior, terminal fate map larva triple mutants active systems active systems wild-type A P T - - - single mutants double mutants - P T - P - anterior bicoid A - T - - T posterior oskar A P - A - - terminal torso additive phenotypes

Maternal effect mutations Figures\Chapter09\DevBio7e09t010.jpg

Zygotic effect mutations Figures\Chapter09\DevBio7e09t020.jpg

bicoid mutant phenotype Embryo from wild-type mother Embryo from bicoid mother Figures\Chapter09\DevBio7e09130.jpg Wild-type Bicoid promotes anterior fates and inhibits posterior fates.

Anterior: bicoid is required for head and thorax Wild type bicoid mutant blastoderm fate map head + thorax abdomen abdomen

Bicoid mRNA localization in embryo (tethered to microtubules) Figures\Chapter09\DevBio7e09141.jpg

Nuclei divide without cell division in Drosophila to produce a syncytial blastoderm embryo Figures\Chapter09\DevBio7e09010.jpg Fig. 9.1

Bicoid protein gradient in syncytial blastoderm embryo - diffuses after translation from localized mRNA - protein unstable Figures\Chapter09\DevBio7e09142.jpg

Transplantation of egg cytoplasm An organizer of the anterior-posterior pattern is located at the anterior pole wt rescue of pattern wt head in the center polarity reversal wt thorax at posterior pole polarity reversal abdomen only polarity normal

bicoid mRNA induces head and thorax bicoid (bcd) gene encodes a homeo-domain transcription factor

Injection of bicoid mRNA: anterior (head) structures at site of injection & reorganization of polarity no head

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Bicoid protein: transcriptional and translational regulator zygotic target genes maternal target mRNA (promotes anterior fates) (inhibits posterior fates)

Transplantation of egg cytoplasm Posterior cytoplasm also has polarizing activity wt rescue of pattern wt head in the center polarity reversal wt thorax at posterior pole polarity reversal wt double abdomen polarity reversal abdomen only polarity normal

Mutations affecting the antero-posterior axis 3 independent maternal systems: anterior, posterior, terminal fate map larva triple mutants active systems active systems wild-type A P T - - - single mutants double mutants - P T - P - anterior bicoid A - T - - T posterior oskar A P - A - - terminal torso additive phenotypes

Nanos is the maternal effector of the posterior system mutant rescued rescued rescue of all posterior-system mutants by injection of nanos mRNA

Embryonic polarity genes Figures\Chapter09\DevBio7e09101.jpg

Figures\Chapter09\DevBio7e09102.jpg

Anterior-Posterior pattern formation in flies Figures\Chapter09\DevBio7e09081.jpg

The Bcd gradient is converted into domains of gene expression Bcd protein binds differentially to enhancers of target genes Different thresholds of Bcd concentration are required to turn on different genes low affinity high affinity target genes are zygotically expressed Gap genes

Bcd gradient and expression domains of target genes bcd mRNA Bcd protein target genes

Expression patterns of proteins encoded by Gap genes Bicoid and Nanos regulate Gap gene expression Figures\Chapter09\DevBio7e09221.jpg Expression patterns of proteins encoded by Gap genes

Gap gene mutants lack different body regions

Gap gene mutants lack different body regions Wild type Krüppel hunchback knirps

The gap genes regulate each other and form domains with distinct combinations of gene expression. Hunchback Krüppel

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Anterior-Posterior pattern formation in flies Figures\Chapter09\DevBio7e09081.jpg

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Wild type fushi tarazu mutant Pair-rule mutants Wild type fushi tarazu mutant Figures\Chapter09\DevBio7e09211.jpg

Even-skipped expression pattern

Modularity of the Drosophila even-skipped promoter 08_18_reporter.gene.jpg 08_18_reporter.gene.jpg

Regulation of expression stripe no. 2 of Even-skipped (eve) hunchback giant eve stripe #2 Krüppel repressor activator parasegment 1 2 3 4 5 multiple binding sites in enhancer of eve repressors activators

Regulation of the Second Stripe of Transcription from the even-skipped Gene Figures\Chapter09\DevBio7e09242.jpg

Regulation of the even-skipped gene Figures\Chapter09\DevBio7e09230.jpg

Fushi tarazu expression Refinement of expression domains over time early Fushi tarazu expression Figures\Chapter09\DevBio7e09250.jpg late Eve, Ftz expression

Refined expression domains in distinct cell rows

Anterior-Posterior pattern formation in flies Figures\Chapter09\DevBio7e09081.jpg

Segment polarity mutants Figures\Chapter09\DevBio7e09202.jpg

Segment polarity mutants

Wingless signaling specifies cell fates in the ventral epidermis Anterior cells make Hair Posterior cells make Naked cuticle Wild type arm mutant

Segment polarity genes – 14 stripes 13 12 A 11 ap 10 L fg 9 hg 8 1 7 2 3 6 4 5 Expression of segment polarity gene wingless

Segments and Parasegments Figures\Chapter09\DevBio7e09190.jpg

The Even-skipped and Fushi tarazu pair-rule transcription factors activate the segment-polarity gene Engrailed

Intercellular feedback maintains pair-rule gene expression states Figures\Chapter09\DevBio7e09262.jpg

Intercellular feedback maintains pair-rule gene expression states =Wnt Figures\Chapter09\DevBio7e09263.jpg

Wnt signaling pathway - + - + - + + - - + - +

Gradients of Wingless and Hedgehog pattern each segment

Anterior-Posterior pattern formation in flies Figures\Chapter09\DevBio7e09081.jpg