Transcript Document
Xenopus laevis The African Clawed Foot Toad QuickT ime™ and a TI FF (Uncompressed) decompressor are needed to see this picture. 36 chromosomes, 3.1x109bp ancestrally tetraploid 4 hr The Xenopus Life Cycle 6 hr 1-2 years 19 hr 110 hr 32 hr 10 hr Oogenesis Ovary filled with eggs triggered by human chorionic gonadotropin 1-2 mm Animal pole QuickTime™ and a TIFF (Uncompressed) decompressor are needed t o see this picture. Female Xenopus Vegetal pole The METRO (MEssage TRansport Organizer) organizes mRNA localizations for Dorsal-Ventral Specification Quic kT ime™ and a TIFF (Unc ompres s ed) dec ompres s or are needed to see thi s pic ture. VegT Oct60 In vivo In vitro Sperm entry point Fertilization QuickTime™ and a YUV420 codec decompressor Ca++toindicator are needed see this picture. Movie D A Nieuwkoop Center/ Spemann Organizer Gray Crescent P V QuickTime™ and a Video decompressor are needed to see this picture. The first cleavage occurs along the plane of cortical rotation The First Cleavages V Split the Embryo on the Three Axes of the Fate Map Cleavage Continues to Form the Blastula QuickTime™ and a Sorenson Video decompressor are needed to see this picture. View from the Animal Pole Twin Frogs Only Along the A-P Axis Shift in the cell cycle Archenteron Gastrulation: Involution and Epiboly Ectoderm Mesoderm Endoderm Movie QuickTime™ and a Cinepak decompressor are needed to see this picture. Gastrulation layers the embryo Ectoderm Mesoderm Endoderm skin brain spinal cord all other neurons sense receptors notochord muscles blood bone sex organs lining of gut lining of lungs lining of bladder liver pancreas Inductive signals Factor Type Source Veg-1 TGF-Beta Vegetal Cytoplasm Activin TGF-Beta Bone Morphogenetic Protein (BMP-4) TGF-Beta Entire Embryo XWint-8 Wnt Middle Embryo Fibroblast Growth Factor (FGF) FGF Middle Embryo Noggin Neural Inducer Spemann Organizer Binds BMP-4 Chordin Neural Inducer Spemann Organizer Binds BMP-4 Spemann Organizer Binds XWnt-8 Frizbee Effect Mesoderm Induction And Embryonic Patterning Induction Signaling molecules The Roles of the Nieuwkoop Center and the Spemann Organizer Veg1 (TGF-B) signaling TGF-Beta/SMAD Signaling The Wnt Pathway Wnt ligands (Wg) Frizzled G-protein coupled receptors (DFz2) P Axin scaffold adenomatous polyposis coli APC GSK3 GSK3 Disheveled (dsh) (signaling intermediate) Glycogen Synthase Kinase 3 (GSK3) Beta-catenin (Arm) (transcription factors) A Key Signaling Pathway in Regulatory Development and Cancer New gene activity -Axin (activates) Dorsalization Wnt -Beta catenin (inactivates) Ventralization TGF-Beta -Veg 1, VegT Failure of Gastrulation (Ectodermal ball) WT Sending the Wrong Signals FGF (Fibroblast Growth Factor) Is also Involved in Mesodermal Induction FGF Overexpression Normal FGF Depletion A Downstream Master Switch MyoD, a myogenic regulator Gastrulation Neural tube closure Tail bud formation QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Movie Tadpole Morphogenesis: Behold, the frog! A Few Questions for Thought •Integrate the contributions of mosaic and regulatory mechanisms in Xenopus. •What is a fate map and how is it applied to metazoan development? Compare and contrast fate maps for our different model organisms. •Describe the molecular bases of inductive signaling via the TGF-Beta and Wnt pathways. •What is the gray crescent, how is it formed and what does it mark? Using your understanding of METRO, suggest an hypothesis for how the gray crescent determines the fate of cells that ultimately inherit this cytoplasm. •Describe the process of gastrulation in Xenopus and the contributions of each of the three key tissue layers to the development of the tadpole body.