Download By the `primary organizer`

Endoderm and primary induction
Human
Figure 11.32(1) Tissue Formation in the Human Embryo Between Days 7
and 11
Figure 11.32(2) Tissue Formation in the Human Embryo Between Days 7
and 11
Figure 11.33(1) Amnion Structure and Cell Movements During Human Gastrulation
Huma
Figure 1.6 Fate Maps of Different Vertebrate Classes at the
Early Gastrula Stage
Figure 1.5 The Similarities and Differences among Different
Vertebrate Embryos
START
PRIMARY
ORGANIZER
LECTURE FROM HERE
Terms (definitions) for Establishment of cells and tissues
(here use lens cells as an example)
• Competence, wherein cells can become lens
precursors if they are exposed to the appropriate
combination of signals.
• Specification, wherein cells have received the
appropriate signals to become lens precursors, but
progression along the pathway to lens can still be
repressed by other signals.
• Commmitment (determination), wherein lens
precursors have entered a differentiation pathway,
and will become lens even in the presence of
inhibitory signals.
• Differentiation, wherein the lens cells leave the
mitotic cycle and express those genes characteristic
of their cell type.
Early dpp/BMP gradients dictate the D/V axis of the entire embryo
Early dpp/BMP gradients dictate the D/V axis of the entire embryo
Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes
(Drosophila) and Deuterostomes (Xenopus) D/V
Later cases of dpp/BMP expression direct specific embryonic tissue inductions
Later cases of dpp/BMP expression direct specific embryonic tissue inductions
Later cases of dpp/BMP expression direct specific embryonic tissue inductions
Sea Urchin
BMP-2/
BMP-4
Nodal
Figure 3.14 Roux’s Attempt to Demonstrate Mosaic Development
Wilhelm Roux, 1888
Figure 3.11 Conditional Specification
Two critical inductions:
Formation of the primary organizer
Action of the primary organizer
Neurulation is induced (By the ‘primary organizer’)
-1. The primary organizer induces
neurulation and axis formation
-2. The primary organizer itself
arises from a previous induction
-1. The primary organizer induces neurulation and axis formation
-The dorsal lip of the blastopore contains the primary organizer
-1. The primary organizer induces neurulation and axis formation
-The dorsal lip of the blastopore contains the primary organizer
-1. The primary organizer induces neurulation and axis formation
-The dorsal lip of the blastopore contains the primary organizer
-1. The primary organizer induces neurulation and axis formation
Figure 10.21(1) Organization of a Secondary Axis by Dorsal Blastopore Lip Tissue
-1. The primary organizer induces neurulation and axis formation
Figure 10.21(1) Organization of a Secondary Axis by Dorsal Blastopore Lip Tissue
Amphibian
-1. The primary organizer induces neurulation and axis formation
Source of primary organizer shown on fate map
Amphibian
-The primary organizer induces
neurulation and axis formation
-The primary organizer itself
arises from a previous induction
-The primary organizer itself arises from a previous induction
OR . . . where does the ‘primary organizer’ come from?
-The primary organizer itself arises from a previous induction
Experiment at the 32-cell stage
Contains the
Nieuwkoop center
-The primary organizer itself arises from a previous induction
The primary organizer is induced by the Nieuwkoop center
(a tissue with an endodermal fate)
The primary organizer arises due to an induction from the Nieuwkoop center
How does the Nieuwkoop center arise?
Spemann, 1938 - baby’s hair ligature
The primary organizer arises due to an induction from the Nieuwkoop center
How does the Nieuwkoop center arise?
The primary organizer arises due to an induction from the Nieuwkoop center
How does the Nieuwkoop center arise?
The primary organizer arises due to an induction from the Nieuwkoop center
How does the Nieuwkoop center arise?
The primary organizer arises due to an induction from the Nieuwkoop center
How does the Nieuwkoop center arise?
Contains the
Nieuwkoop center
Figure 11.18 Formation of the Nieuwkoop Center in Frogs And Chicks
Figure 11.19 Formation of Hensen’s Node From Koller’s Sickle
Figure 11.20(1) Induction of a New Embryo by Transplantation of
Hensen’s Node
THE ORGANIZER IS IN THE HENSEN’S NODE
Mammal
Zebrafish
Figure 11.7 Convergence and Extension in the Zebrafish Gastrula
Zebrafish
Figure 11.8 The Embryonic Shield as Organizer in the Fish Embryo
Figure 1.6 Fate Maps of Different Vertebrate Classes at the
Early Gastrula Stage
All have homologous
organizers
Figure 1.5 The Similarities and Differences among Different
Vertebrate Embryos