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Chapter 21 - 204-325 1 Summary of the Last lecture During...

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Unformatted text preview: 204-325 1 Summary of the Last lecture During the development of multicellular eukaryotes, each specialized cells still contains the entire genome, although only part of it is expressed in any given cell at certain time. Gene expression is controlled by transcriptional regulation and posttranscriptional regulations in eukaryotes. Transcriptional activator proteins bind enhancer DNA sequences and work in combinatorial way to initiate transcription. Chromatin structure and histone modifications also regulate transcription. Posttranscriptional regulation also contributes to gene expression: RNA processing, RNA transport, RNA stability, translation, and protein stability. RNA interference and micro RNA are newly discovered mechanisms for regulating RNA stability and translation. 2 Today's Topics 1. Developmental Genetics 2. Model Organisms 3. Molecular Mechanism of Sex Determination in Drosophila 4. Development of the Drosophila Body Plan 3 Topic 1 Developmental Genetics 4 Developmental Genetics Developmental genetics studies gene regulations responsible for transforming a single cell federalized egg into a complex multicellular organism. 5 Progressions through Life Cycle are under Genetic Control How does gene control the changes? 6 Fate Map: Projections of What Embryonic Cells will Become 7 Fate Map of the Zebrafish Central Nervous System 8 Cell Fate Determination and Cell Differentiation Determination: Cell fate has been specified by molecular changes, although the cell has not changed its shape, structure and function. Cell is committed to become a certain type. Differentiation: Implementation of the cell fate determination results in measurable changes. Cell becomes a certain type. Determination Differentiation c NeuroD Expression 9 Topic 2 Model Organisms 10 Model Organisms 11 Saccharomyces cerevisiae 12 Caenorhabditis elegans 13 Drosophila melanogaster 14 Danio rerio 15 Mus musculus 16 Arabidopsis thaliana 17 Model Organisms A single, freeliving cell, only 3 microns in diameter (4,000 of them lined up would measure an inch) A multicellular animal, 1 millimeter (0.04 in.) long A multicellular animal with complex behavior, 4 millimeters (0.16 in.) long Our closest relative among model organisms, 170 millimeters (6.6 in.) long 5-6 feet tall Reproduces by budding and doubles every 90 minutes Lifespan: 2-3 weeks. A new generation every three days Lifespan: 2-3 months. A new generation every 10 days Lifespan: 2 years. A new generation every 9 weeks Lifespan: 60-70 years. A new generation every 20-25 years 18 Topic 3 Molecular Mechanism of Sex Determination in Drosophila 19 Chapter 3: Many Ways of Sex Determination Genetic Sex Determination XY System: XY (or XO) , XX Y determination: mammal (including human) X to autosome set ratio: fly, worm, some plant WZ System: ZZ , WZ bird, butterfly, moth, some fish Diploidity / Haplodity: Diploid , Haploid ant, bee, wasp yeast mating type a and Neurospora A and a bacteria F+ and FChromosome Difference (Genotypic) Genic determination (alleles), Syngamous Mating Environmental Sex Determination One turtle species: 320C , 280C 20 Chapter 3: X to A Determines Sex in Drosophila melanogaster X:A 1 Female X:A 0.5 Male 1 > X:A > 0.5 Intersex 21 Chapter 20: Alternative Splicing 22 Chapter 20: Alternative Splicing 23 How is X:A ratio read? XX AA X AA > < 24 Activation of Sex-lethal (Sxl) by sisterless Homodimer Only in Female SXL 25 Regulation of Sex-lethal (Sxl) Splicing by SXL Protein 26 Regulation of transformer (tra) Splicing by SXL Protein TRA 27 Regulation of doublesex (dsx) Splicing by TRA Protein TRA Femaleness 28 Maleness A Cascade of Alternative Splicing Leads to Sex Determination 29 Sex Determination in Drosophila by Alternative Splicing 30 Animation 1: Sex Determination and Dosage Compensation 31 Topic 4 Development of the Drosophila Body Plan 32 Development of an Adult Drosophila From a Fertilized Egg 33 Programmed Gene Regulation Defined the Body Plan : 0 hr Segmentation 5 hour Identity Assignment : 10 days 34 First 3 Hour Embryonic Development in Drosophila : Thousands of Nuclei in 1 cell 35 bicoid is a Morphogen: Long Range Control by Protein Gradient 36 bicoid is an Anterior Morphogen; nanos is a Posterior Morphogen A P Bicoid mRNA Nanos mRNA Bicoid protein Nanos protein 37 Segmentation Gene Functions Revealed by Mutations 38 A Cascade of Gene Regulation Leads to Segmentation bicoid Morphogen Establish anterior-posterior gradient of embryo hunchback Krppel Knirps tailless giant Gap genes Organize cells into groups of segments along anteriorposterior axis. Pair-rule genes Organize cells into individual segments. hairy even-skipped runt engrailed hedgehog wingless cubitus interruptus Segment polarity genes Establish anterior-posterior within each segment. 39 Gene Regulation Cascade for Setting Up Segmentation Maternal Morphogen Gap Pair-Rule Segment Polarity 40 Adult Structures Derived From Imaginal Discs 41 Hox (Homeotic) Genes Assign Segmental Identities Fate Map Fertilized Egg Adult Embryo Larva 42 Mutations in Ultrabithorax Gene (Homeotic Mutation) 43 Mutations in Antennapedia Gene (Homeotic Mutation) Antennapedia Mutant 44 Animation 2: Drosophila Body Plan Development 45 Conservation of Hox Genes and Their Functions 46 Mouse and Human Have Four Hox Clusters 47 Most Animals have Hox Genes 48 Summary Development of an organism is controlled by programmed expression of genes. Model organisms are used in developmental genetics to analyze gene regulation. Cell fate determination is followed by differentiation. Drosophila sex determination is the result of three consecutive alternative splicing. Drosophila body plan is progressively defined by morphogen gradients, segmentation genes and Hox genes. Segmentation genes include gap genes, pair-rule genes and segment polarity genes. Hox genes assign segmental identities in both Drosophila and mouse. 49 ...
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