Drosophila melanogaster
2.5mm
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Movie
Adult cDNA Larval cDNA
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Developmentally-Regulated Gene Expression
The Fly Genome3 autosomal pairs (2,3,4)
Sex chromosomes XX, XY
165Mb14,000 genes
50% have a human homolog61% of human disease genes have a fly
counterpart
Early Development Disconnects Mitosis from Cytokinesis
GFP-tau marks microtubules
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90 mins post-fertilization
Pole Cells Inherit Polar Ganules
Containing Oscar
Posterior end
Anterior end
120 minutes post-fertilization
Cellularization Traps Nuclei in Different Microenvironments
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Immunolocalization of Bicoid, Even-skipped and Caudal Proteins
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D
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Cascades of Gene
Activity Set up the
Drosophila Body Plan
Maternal Coordinate GenesBicoid, Nanos, Caudal
Anterior-Posterior, Dorsal-Ventral Axes
Gap GenesHunchback, Kruppel, Knirps
Anterior/Middle/Posterior
Pair Rule Genes (7 stripes)Even-skipped, Hairy, Fushi Tarazu
Segmentation
Segment Polarity GenesWingless, Hedgehog, Engrailed
Define the A-P axis of 14 segments
Homeotic GenesDefine the identity of the segments
Events of Embryogenesis
1-4 0:00-2:10 hr Cleavage
5 2:10-2:50 hr Cellular Blastoderm
6-7 2:50-3:10 hr Gastrulation
8-11 3:10-7:20 hr Germ Band Elongation
12-13 7:20-10:20hr Germ Band Retraction
14-15 10:20-13:00hrHead involution and
dorsal closure
16-17 13:00-22:00hr Differentiation
Stage Timing Landmark event
Gastrulation
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Blastocoel
Twist is a bHLH transcription factor that will later turn on fibroblast growth factor
(FGF) receptors
Animation
"The most important event in your life is not birth, marriage, or death, but gastrulation.”
- L. Wolpert
Establishing the Mesoderm
3 hours post-fertilization
Followed by germ cell placement and introgression of the
endoderm
Homeotic Mutations
Wild-type ultrabithorax mutant
converts halteres to wings
Convert One Segmental Identity into Another
Wild-type Antennapedia
A Few Questions for Thought•How might enhancer elements (studied in the Arabidopsis lab) “simplify” issues of gene expression multicellular organisms? How might they promote evolutionary change?•In a proverbial case of the chicken or the egg, how does Drosophila pattern its the embryo?•Describe the specific contributions of Bicoid, Caudal, Hunchback and Nanos to early embryonic development Extend your description to include how a segmented animal is formed and how those segments are determined to specific identities by cascades of gene expression.•Review the landmark events of morphogenesis as the hollow ball of cells called the blastoderm is converted into a larva. •Explain how the larva in turn is converted into an adult fly in metamorphosis. What are the roles of homeotic genes in this process?
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