Drosophila melanogaster

2.5mm

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The Life Cycle

1-2 weeks

36hr

60 hr

12 hr

Adult cDNA Larval cDNA

2 2 3 3

4 4

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

Developmentally-Regulated Gene Expression

Oogenesis

Filaments

0.5mm

Maternal Effect Genes

Oscar mRNA

Nurse cells Oocyte

Gurken (TGF-alpha) mRNA

Anterior-Posterior Gradients

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

A P

D

V

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

Morphogenesis

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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

The (Segmented) Larva

Head Tail

3+3+8=14

Metamorphosis

24 hours post-fertilization

Homeotic Mutations

Wild-type ultrabithorax mutant

converts halteres to wings

Convert One Segmental Identity into Another

Wild-type Antennapedia

Homeotic Genes

DrosophilaMouseDrosophilaXenopusC. 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?