xenopus laevis 36 chromosomes, 3.1x10 9 bp ancestrally tetraploid the african clawed foot toad
TRANSCRIPT
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Xenopus laevis
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36 chromosomes, 3.1x109bpancestrally tetraploid
The African Clawed Foot Toad
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4 hr
6 hr
10 hr
19 hr
32 hr
110 hr
1-2 yearsThe
Xenopus Life
Cycle
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Oogenesis
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Ovary filled with eggs
Animal pole
Vegetal poleFemale Xenopus
1-2 mm
triggered by human chorionic gonadotropin
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The METRO
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Oct60
VegT
(MEssage TRansport Organizer)organizes
mRNA localizations for Dorsal-Ventral Specification
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FertilizationQuickTime™ and a
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In vivo
In vitro
Sperm entry point
Ca++ indicator
Movie
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Gray Crescent
The first cleavage occurs along the plane of cortical rotation
Nieuwkoop Center/
Spemann Organizer
A P
D
V
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The First Cleavages
V
Split the Embryo on the Three Axes of the Fate Map
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Cleavage Continues to
Form the Blastula
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View from the Animal Pole
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Twin Frogs
Only Along the A-P Axis
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Shift in the cell cycle
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Gastrulation:Involution
and Epiboly
EctodermMesodermEndoderm
Archenteron
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Gastrulation layers the embryo
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Ectoderm Mesoderm Endoderm skin notochord lining of gut brain muscles lining of lungs spinal cord blood lining of bladder all other neurons bone liver sense receptors sex organs pancreas
Movie
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Inductive signals
Factor Type Source Effect
Veg-1 TGF-Beta Vegetal Cytoplasm
Mesoderm Induction
And Embryonic Patterning
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
Frizbee Spemann Organizer Binds XWnt-8
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Induction Signaling molecules
Veg1 (TGF-B) signaling
The Roles of the Nieuwkoop Center and the Spemann Organizer
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TGF-Beta/SMAD Signaling
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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
PAxin
APC
GSK3
A Key Signaling Pathway in Regulatory Development and Cancer
scaffold
adenomatous polyposis coli
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Sending the Wrong Signals
-Veg 1, VegT WT
Failure of Gastrulation(Ectodermal ball)
Dorsalization
Ventralization
-Axin(activates)
-Beta catenin(inactivates)
Wnt
TGF-Beta
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FGF (Fibroblast Growth Factor)
FGFOverexpression
Normal
FGF Depletion
Is also Involved in Mesodermal
Induction
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MyoD, a myogenic regulator
A Downstream
Master Switch
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GastrulationNeural tube closureTail bud formation
Movie
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Tadpole
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Morphogenesis:Behold, the frog!
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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.