1. Xenopus laevis 36 chromosomes, 3.1x10 9 bp ancestrally tetraploid The African Clawed Foot Toad

2. 4 hr 6 hr 10 hr 19 hr 32 hr 110 hr 1-2 years The Xenopus Life Cycle

3. Oogenesis Ovary filled with eggs Animal pole Vegetal pole Female Xenopus 1-2 mm triggered by human chorionic gonadotropin

4. The METRO Oct60 VegT (MEssage TRansport Organizer) organizes mRNA localizations for Dorsal-Ventral Specification

5. Fertilization In vivo In vitro Sperm entry point Ca++ indicator Movie

6. Gray Crescent The first cleavage occurs along the plane of cortical rotation Nieuwkoop Center/ Spemann Organizer A P DVDV

7. The First Cleavages V Split the Embryo on the Three Axes of the Fate Map

8. Cleavage Continues to Form the Blastula View from the Animal Pole

9. Twin Frogs Only Along the A-P Axis

10. Shift in the cell cycle

11. Gastrulation: Involution and Epiboly Ectoderm Mesoderm Endoderm Archenteron

12. Gastrulation layers the embryo Movie

13. Inductive signals FactorTypeSourceEffect Veg-1TGF-BetaVegetal Cytoplasm Mesoderm Induction And Embryonic Patterning ActivinTGF-Beta Bone Morphogenetic Protein (BMP-4) TGF-BetaEntire Embryo XWint-8WntMiddle Embryo Fibroblast Growth Factor (FGF) FGFMiddle Embryo NogginNeural InducerSpemann OrganizerBinds BMP-4 ChordinNeural InducerSpemann OrganizerBinds BMP-4 FrizbeeSpemann OrganizerBinds XWnt-8

14. Induction Signaling molecules Veg1 (TGF-B) signaling The Roles of the Nieuwkoop Center and the Spemann Organizer

15. TGF-Beta/SMAD Signaling

16. Wnt ligands (Wg) Frizzled G-protein coupled receptors (DFz2) Disheveled (dsh) (signaling intermediate) Glycogen Synthase Kinase 3 (GSK3) Beta-catenin (Arm) (transcription factors) New gene activity The Wnt Pathway GSK3 P Axin APC GSK3 A Key Signaling Pathway in Regulatory Development and Cancer scaffold adenomatous polyposis coli

17. Sending the Wrong Signals -Veg 1, VegT WT Failure of Gastrulation (Ectodermal ball) Dorsalization Ventralization -Axin (activates) -Beta catenin (inactivates) Wnt TGF-Beta

18. FGF (Fibroblast Growth Factor) FGF Overexpression Normal FGF Depletion Is also Involved in Mesodermal Induction

19. MyoD, a myogenic regulator A Downstream Master Switch

20. Gastrulation Neural tube closure Tail bud formation Movie

21. Tadpole

22. Morphogenesis: Behold, the frog!

23. 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.