Drosophila melanogaster

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Drosophila melanogaster
2.5mm
Movie
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The Life Cycle
12 hr
1-2 weeks
36hr
60 hr
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The Fly Genome
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3 autosomal pairs (2,3,4) Sex chromosomes XX, XY
165Mb14,000 genes 50 have a human homolog 61
of human disease genes have a fly counterpart
Developmentally-Regulated Gene Expression
Adult cDNA Larval cDNA
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Developmentally-Regulated Gene Expression
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Oogenesis
Filaments
0.5mm
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Maternal Effect Genes
Nurse cells Oocyte
Oscar mRNA
Gurken (TGF-alpha) mRNA
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Anterior-Posterior Gradients
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Early Development Disconnects Mitosis from
Cytokinesis
Movie
GFP-tau marks microtubules
90 mins post-fertilization
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Pole Cells Inherit Polar Ganules Containing Oscar
Posterior end Anterior end
120 minutes post-fertilization
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Cellularization Traps Nuclei in Different
Microenvironments
D V
A P
Immunolocalization of Bicoid, Even-skipped and
Caudal Proteins
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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
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Events of Embryogenesis
Stage Timing Landmark event
1-4 000-210 hr Cleavage
5 210-250 hr Cellular Blastoderm
6-7 250-310 hr Gastrulation
8-11 310-720 hr Germ Band Elongation
12-13 720-1020hr Germ Band Retraction
14-15 1020-1300hr Head involution and dorsal closure
16-17 1300-2200hr Differentiation
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Morphogenesis
Movie
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Gastrulation
Establishing the Mesoderm
Animation
Blastocoel
"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
Twist is a bHLH transcription factor that will
later turn on fibroblast growth factor (FGF)
receptors
3 hours post-fertilization
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The (Segmented) Larva
33814
Head Tail
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Metamorphosis
24 hours post-fertilization
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Homeotic Mutations
Wild-type ultrabithorax
mutant
converts halteres to wings
Convert One Segmental Identity into Another
Wild-type Antennapedia
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Homeotic Genes
Drosophila Mouse Drosophila Xenopus C. elegans
Conserved homeobox DNA binding domain
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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?