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 Human

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

Figure Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus) D/V Early dpp/BMP gradients dictate the D/V axis of the entire embryo

Later cases of dpp/BMP expression direct specific embryonic tissue inductions

Sea Urchin Nodal BMP-2/ BMP-4 Later cases of dpp/BMP expression direct specific embryonic tissue inductions

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

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 -1. The primary organizer induces neurulation and axis formation

Amphibian

Source of primary organizer shown on fate map -1. The primary organizer induces neurulation and axis formation

-The primary organizer induces neurulation and axis formation -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

Contains the Nieuwkoop center Experiment at the 32-cell stage

-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, 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 Formation of the Nieuwkoop Center in Frogs And Chicks

Figure 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

Figure 11.7 Convergence and Extension in the Zebrafish Gastrula Zebrafish

Figure 11.8 The Embryonic Shield as Organizer in the Fish Embryo Zebrafish

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