2.5mm

Drosophila melanogaster

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The Life Cycle 1-2 weeks 12 hr 36hr 60 hr

2 2 3 3 4 4 165Mb 14,000 genes 50% have a human homolog 61% of human disease genes have a fly counterpart The Fly Genome 3 autosomal pairs (2,3,4) Sex chromosomes XX, XY Developmentally Regulated 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 QuickTime™ and a Cinepak decompressor are needed to see this picture.

90 mins post-fertilization GFP-tau marks microtubules

Posterior end Pole Cells Inherit Polar Ganules Containing Oscar Anterior end 120 minutes post-fertilization

D Cellularization Traps Nuclei in Different Microenvironments QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

A V Immunolocalization of Bicoid , Even-skipped and Caudal Proteins P

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 5 6-7 0:00-2:10 hr 2:10-2:50 hr 2:50-3:10 hr Cleavage Cellular Blastoderm Gastrulation 8-11 3:10-7:20 hr Germ Band Elongation 12-13 14-15 16-17 7:20-10:20hr Germ Band Retraction 10:20-13:00hr 13:00-22:00hr Head involution and dorsal closure Differentiation

Morphogenesis QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture.

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Gastrulation Establishing the Mesoderm Animation Blastocoel QuickTime™ and a QuickT i me™ and a Sorenson Video decompressor are needed t o s ee thi s pi c ture.

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"The most important event in your life is not birth, marriage, or death, but gastrulation.” - L. Wolpert Twist is a bHLH transcription factor that will later turn on fibroblast growth factor (FGF) receptors 3 hours post-fertilization Followed by germ cell placement and introgression of the endoderm

Head The (Segmented) Larva 3+3+8=14 Tail

24 hours post-fertilization Metamorphosis

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?