Genetic toolkit F07

Genetic toolkit F07 - 1 The Genetic Toolkit for Development...

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Unformatted text preview: 1 The Genetic Toolkit for Development What is the genetic toolkit? • Subset of genes in the genome used to form & pattern the body. • Two classes of genes have the most global & profound effects: a) Transcription factors: regulate expression of other genes. b ) Signaling molecules : mediate short & long-range interactions between cells. • Expression patterns of these “pattern-forming” genes mark locations of many classically-defined signaling regions in the embryo. • The proteins encoded by these genes control the formation, identity & patterning of most major features of animal design and diversity. Embryonic Axes Dorsal-Ventral (Dorso-ventral) Front to back Anterior-Posterior (Antero-posterior) Head to tail a.k.a. Cranial-caudal Anterior Posterior Ventral Dorsal Proximal-Distal : Proximal: close to body Distal: far from body Proximal Distal 2 Before the toolkit • The Cut and Paste approach: Embryologists used experimental manipulation (ablation, transplantation) to define properties of specific tissues. • Organizers: Regions of embryo with long- range effects on fate of surrounding tissue. Germ layers : The main divisions of tissue types in multicellular organisms. Ectoderm : Outer layer. Forms skin & nervous system Endoderm : Inner layer. Forms epithelial tissue lining the gut. Mesoderm : Middle Layer. Forms muscle, skeleton, connective tissue, excretory organs, gonads. Diploblastic organisms (eg. Coelenterates; jellyfish, hydra, coral) have two germ layers, ectoderm and endoderm. Triploblastic organisms (all higher animal groups) have mesoderm between these two layers Gastrulation : Cellular rearrangements that transform the 2-germ cell embryo (ectoderm & endoderm) into a 3-germ cell embryo (+ mesoderm). 3 Gastrulation is initiated by Spemann’s organizer Blastopore lip Organizer Dorsal view Dorsal Ventral Induction of secondary axis by dorsal blastopore lip tissue-Spemann & Mangold, 1924 4 Zone of Polarizing Activity (ZPA) - patterns the A/P axis • Discovered 40 years ago by simple surgeries – John Saunders • Transplant mesoderm from posterior bud to anterior – Result: mirror-image duplication of digits • Repolarizes limb bud – “organizer” for limb How is long-range signaling mediated? • Organizers are sources of signals known as morphogens (they generate morphology). • Morphogen : Substance whose concentration varies across a tissue or field, and to which cells respond differently at different concentrations. • Morphogens are secreted factors that are produced by a localized signaling region, and diffuse over a distance....
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This note was uploaded on 04/11/2008 for the course ZOO 3003C taught by Professor Cohn during the Spring '08 term at University of Florida.

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Genetic toolkit F07 - 1 The Genetic Toolkit for Development...

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