Neural Induction Flashcards
How is a piece of tissue set apart in the early embryo as either PNS or CNS?
Neural plate/tube indicates tissue that will become neural. The plate folds to become a tube with 3 strips of primary neural precursors, ventral, intermediate and dorsal
When does neural and non-neural ectoderm become morphologically distinct?
During gastrulation. Comparison of fate of animal cap between pregastrula and gastrula
Where does gastrulation begin?
At the blastophore
How is the antero-posterior of tissue determined?
By the involution time. The mesoderm involutes along the equator beginning at the future dorsal side.
Briefly outline the process of neural plate formation
The embryo divides continually to become blastula. Blastocoel forms, pre-gastrula, gastrulation, gastrula, neurula - this is where the neural plate is formed.
How is the decision made to become neural or epidermis?
Spemann and Mangold 1924 expt with newt. Dorsal blastophore lip is responsible for neural induction.
What is induction?
The process by which the presence of one tissue influences the development of others.
What role does Beta-catenin play?
When sperm enters the egg at SEP, the sperm aster combined with the maternal aster causes cortical rotation. beta catenin is stabilised by Wnt signalling at the point where the Spemann’s organiser later forms (in amphibians)
How is all mesoderm specified?
TGF/Nodal signalling specifies mesoderm in dose-dependent manner. Organiser is specified by high nodal, high b-catenin. Ventral mesoderm specified by low nodal, Veg-T, vg-1.
Briefly outline the TGFb/nodal pathway
Ligands: Nodal/activin and BMPs. Receptors: some common, some specific. Intracellular messengers: regulated Smads. Smad4 coeffector is necessary for nuclear translocation.
How was Noggin discovered?
Sharf & Gerhart 1980 - UV radiation of vegetal pole of newly fertilised embryo prevented microtubule assembly, no cortical rotation and only development of ventral structures. Gimlich & Gerhert 1984 - injection of vegetal blastomeres induced dorsal structures. Smith & Harland 1992 - injection of Poly(A+) RNA could rescue dorsal development. Found Noggin (RNA).
How was Follistatin discovered?
Hemmati-Brivanlou et al. 1994. found that dom. neg. activin receptor turns prospective ectoderm into neural tissue. deduced that activin is an inhibitor of neuralisation. suggested that inhibition of activin or other TGFb molecules may induce neuralisation.
What is follistatin?
Activin inhibitor - induces neural tissue. Located in Spemann’s organiser and notochord. In early embryo found in dorsal midline. activin actually induces follistatin
How was Chordin discovered?
Sasai et al. 1994. Injection goosecoid mRNA (homeobox containing gene) induced entire secondary axis when injected into the ventral side of Xenopus embryo. encodes a DNA binding protein. Differential screen found gene activated by gsc - secondary response gene to activin treatment. its a putative extracellular protein that has axis-forming abilities.
Explain the default model.
The default model states that the animal cap is neural. The role of the organiser is to prevent BMPs from turning neural-fated tissue into epidermal tissue. Wilson and Hermatti-Brivanlou 1995 - animal cap intact = epidermis, dissociated = neural. Adding BMP4 to dissociated neural tissue = epidermal tissue.
