Drosophila melanogaster 2.5mm Movie

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

Adult cDNALarval cDNA Developmentally- Regulated Gene Expression The Fly Genome 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

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

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 1-40:00-2:10 hrCleavage 52:10-2:50 hrCellular Blastoderm 6-72:50-3:10 hrGastrulation 8-113:10-7:20 hrGerm Band Elongation :20-10:20hrGerm Band Retraction :20-13:00hr Head involution and dorsal closure :00-22:00hrDifferentiation Stage Timing Landmark event

Morphogenesis Movie

Gastrulation 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 HeadTail 3+3+8=14

Metamorphosis 24 hours post-fertilization

Homeotic Mutations Wild-typeultrabithorax mutant converts halteres to wings 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?