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2.5mm Drosophila melanogaster QuickTime™ and a None decompressor are needed to see this picture. Movie 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 QuickTime™ and a Cinepak decompressor are needed to see this picture. 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 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 QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture. Movie Gastrulation Establishing the Mesoderm Animation Blastocoel QuickTime™ and a Sorenson Video decompressor are needed to see this picture. QuickTi me™ and a P lanar RGB decom pressor are needed to see t his pict ure. 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?