2.5mm
Drosophila melanogaster
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The Life Cycle
12 hr
1-2 weeks
36hr
60 hr
2 2 3 3
The Fly Genome
4
4
3 autosomal pairs (2,3,4)
Sex chromosomes XX, XY
165Mb
14,000 genes
50% have a human homolog
61% of human disease genes have a fly
counterpart
DevelopmentallyRegulated Gene
Expression
Adult cDNA
Larval cDNA
Developmentally-Regulated
Gene Expression
Oogenesis
Filaments
0.5mm
Nurse cells
Oocyte
Oscar mRNA
Maternal Effect
Genes
Gurken (TGF-alpha)
mRNA
Anterior-Posterior Gradients
Early Development Disconnects
Mitosis from Cytokinesis
Movie
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GFP-tau marks microtubules
90 mins post-fertilization
Posterior end
Anterior end
120 minutes post-fertilization
Pole Cells Inherit
Polar Ganules
Containing Oscar
Cellularization Traps Nuclei in
Different Microenvironments
D
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A
P
V
Immunolocalization of Bicoid, Even-skipped and Caudal Proteins
Cascades
of Gene
Activity Set
up the
Drosophila
Body Plan
Maternal Coordinate Genes
Bicoid, Nanos, Caudal
Anterior-Posterior, Dorsal-Ventral Axes
Gap Genes
Hunchback, Kruppel, Knirps
Anterior/Middle/Posterior
Pair Rule Genes (7 stripes)
Even-skipped, Hairy, Fushi Tarazu
Segmentation
Segment Polarity Genes
Wingless, Hedgehog, Engrailed
Define the A-P axis of 14 segments
Homeotic Genes
Define the identity of the segments
Events of Embryogenesis
Stage
Timing
Landmark event
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
10:20-13:00hr
Head involution and
dorsal closure
16-17
13:00-22:00hr
Differentiation
Morphogenesis
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Gastrulation
Establishing the Mesoderm
Animation
Blastocoel
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Twist is a bHLH transcription factor that
will later turn on fibroblast growth factor
(FGF) receptors
3 hours post-fertilization
"The most important
event in your life is not
birth, marriage, or death,
but gastrulation.”
- L. Wolpert
Followed by germ
cell placement and
introgression of the
endoderm
The (Segmented) Larva
3+3+8=14
Head
Tail
Metamorphosis
24 hours post-fertilization
Wild-type
ultrabithorax
mutant
converts halteres to wings
Homeotic Mutations
Convert One Segmental Identity into Another
Wild-type
Antennapedia
Homeotic Genes
Drosophila
Mouse
Drosophila
Xenopus
C. elegans
Conserved homeobox DNA binding domain
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?