420 the only type of signals involved are vertical

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Unformatted text preview: rt 2e, Fig. 4.20 • The only type of signals involved are vertical signals. • Neural structures form appropriate to the type of mesoderm implanted. Conclusion: vertical signals can pattern neural ectoderm. Neural Induction: Summary Gilbert 9e, Fig. 7.35 ❶ In the trunk, BMP inhibitors result in future spinal cord. ❷ Wnt inhibitors lead to future brain (anterior neural tube). ❸ Wnts, FGF & retinoic acid (RA) posteriorize the spinal cord. cerberus promotes brain derivatives Gilbert 8e, Fig. 10.37 mRNA overexpression of cerberus leads to formation of ectopic brain structures Neural induction involves multiple signals Gilbert 9e, Fig. 7.30 Spemann: The Organizer The organizer forms on the dorsal side of the embryo. It is capable of inducing cells around it to become neural ectoderm. Its cells come to lie under the future ectoderm during gastrulation. Gilbert 7e, Fig. 10.21 The frog blastula has superficial and deep cells superficial cells blastocoel deep cells Superficial cells are epithelial cells (joined by junctions). Deep cells are more loosely organized. adapted from Alberts et al, 3e, Fig. 21.4 Amphibian Gastrulation- Overview “Animal cap” Gilbert, 9e, Fig. 7.6 The animal cap makes ectoderm. Gastrulation initiates at the dorsal blastopore lip. Bottle cells help to initiate lip formation. Amphibian Gastrulation- Overview Gilbert, 9e, Fig. 7.6 The mesoderm involutes beneath the ectoderm. The archenteron (primitive gut) begins to form. The blastocoel and what was the animal pole (AP) are displaced towards the future anterior (at the left). Amphibian Gastrulation- Overview Anterior Gilbert, 9e, Fig. 7.6 Endomesoderm comes to lie at the future anterior. Amphibian Gastrulation- Overview Gilbert, 9e, Fig. 7.6 Head and other mesodermal mesenchyme forms Amphibian Gastrulation- Overview Animal cap Blastocoel Dorsal blastopore lip Archenteron Ewald, A. J. et al. Development 2004;131:6195-6209 [see Gilbert 9e, Fig. 7.6] Gastrulation closes the yolk plug The ectoderm spreads to cover over the endoderm, leaving a ro...
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