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Lecture 16 - 1 Despite vast differences in appearance and...

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1. Despite vast differences in appearance and anatomy animals have in common a “toolkit” of genes that govern development. 2. The development of the growing embryo and its body parts takes place in a spatially and temporally ordered progression. 3. Spatially restricted patterns of gene expression are products of combinatorial regulation . 4. Modularity of cis-acting regulatory elements allows for independent spatial and temporal control of toolkit- gene expression and functions.
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Homeotic mutants of Drosophila melanogaster Homeosis : the replacement of one body part by another (homeotic transformation). wt Ultrabithorax mutant Antennapedia mutant
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Organizers in animal embryos – Early study of embryonic development Figure 12-2 ZPA: zone of polarizing activity Transplantation of one part of the embryo to another site on a recipient embryo… Result: induction of the surrounding tissue to form different specific structures. ventral Vertebral limb bud dorsal ventral dorsal
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Life cycle of Drosophila Model Organism: Drosophila Imaginal disks: contained within the body of the larva, there are pairs of discs that will form structures on the outside of the adult body (for instance, the wings, legs or antennae).
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Getting oriented: relationship between adult and embryonic body axes As we will be talking about how ‘morphogen’ concentration gradients affect development we need to be aware of the general architecture of the embryo and how this relates to the adult body. Anterior : situated near or toward the head or part most nearly corresponding to a head Posterior : situated behind Dorsal : relating to or situated near or on the back especially of an animal or of one of its parts Ventral : being or located near or on the anterior or lower surface of an animal opposite the back
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Homeotic transformation affects both members of bilateral pairs in serially reiterated structures Serially reiterated structures : body parts that are members of repeated series, such as digits, ribs teeth, limbs and segments. Antennapedia mutant WT Extra vertebrae Extra structures
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Homeotic transformations arise from both loss-of-function and gain-of function mutations… Ultrabithorax ( Ubx ) gene acts in the developing hind wing to promote hind wing development AND to suppress forewing development. Loss-of-function mutations in Ubx transform the hind wing into a forewing. Dominant gain-of-function mutations in Ubx (leading to its expression in the forewing) transform the forewing into a hind wing. Similarly, gain-of-function mutations in the Antennapedia ( Antp ) gene causes antenna-to-leg transformation. Likewise body segment identity may be transformed…
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Ubx expression in the forewing and haltere (hind” wing” structure) Antibody to Ubx protein is conjugated to fluorophore for imaging (immunolocalization).
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Hox genes regulate the identity of body parts Eight loci have been identified that affect the identity of body segments and their associated structures as seen in the adult fly.
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