Induction and Gastrulation Movements in Mammals
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| What is the epiblast? | One of the initial two germ layers that forms at the junction of the amnionic cavity and the yolk blast. It is the layer that surrounds the amionic cavity.
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| What is the hypoblast? | One of the initial two germ layers that forms at the junction of the amnionic cavity and the yolk blast. It is the layer that surrounds the yolk.
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| What does the epiblast give rise to? | The ectoderm (which didn't involute) and the mesoderm (which did involute).
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| What does the hypoblast give rise to? | The endoderm.
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| What is the primitive groove? | The future midline of the embryo. It is the location where the epiblast is involuted into the yolk sac.
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| What is Hensen's node? | It is an area in the anterior end of the primitive grove where involution is most active.
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| What are the 3 germ layers (from outside to inside) | Ectoderm, mesoderm, and endoderm.
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Gastrulation Movements in Amphibians
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| What are the initial 2 cell layers? | Deep cells and superficial cells.
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| What is the area of most active involution? | dorsal blastopore lip
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| __(1)___ cells induce the ___(2)___ cells to become neural cells. | (1) involuted mesodermal midline cells (2) ectodermal
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| In 1924, a graduate student ___(1)___ working with ___(2)___ did experiments that lead to the concept of "neural induction." | (1) Hilde Mangold and (2) Hans Spemann.
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| What cells did Mangold transplant in the newts? | Cells from the dorsal blastopore lip.
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| What happened in Mangold's transplantation experiment? | The transplanted cells induced the host cells to grow a second axis.
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| What happens to ectodermal cells if BMP4 factors are inhibited? | They become neural cells.
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| BMP4 belongs to this superfamily | TGFβ
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| What are 3 potent neural inducers expressed in the Spemann organizer? | Chordin, Noggin, and Follistatin.
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| What do the genes Chordin, Noggin, and Follistatin do? | Antagonize either BMP binding and/or signaling through its receptor.
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| What is the basic signaling pathway of BMP4? | BMP4 receptor activation leads signaling via the cytoplasmic Smads, which activates transcription of target genes.
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| What fate does Smad1 and Smad4 encourage in ectodermal cells? | Epidermal
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| What fate does Smad7 encourage? | Neural
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| Give examples for the cascade of neuralizing transcription factors. | Sox genes (or Xlpou2), Neurogenin, and then NeuroD.
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| Give an example of one of the initial epidermalizing transcription factors. | Msx1, GATA1, or Vent
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| What is different in the neural induction of invertebrates? | The BMP4 signal is dorsal and the inhibitors are ventral. Thus neural structures develop on the ventral side.
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| What are three reasons that neural induction via the BMP4 pathway is not the whole story? | 1) The Spemann Organizer expresses other neural inducing activity that have nothing to do with BMP4. 2) Mutations in some of BMP4 molecular pathways only have mild effects. 3) In chicks, FGF appears to play a larger role in neural induction.
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| Give an example of two neural-inducing growth factors. | FGF, IGF, HGF, EGF
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| Wnt inhibitors play a larger role in ___. | Early induction of anterior neural structures (brain).
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Mammialian Neural Induction
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| In the mouse embryo, what additional factors are needed for anterior neural fates? | Nodal inhibitors (eg. Lefty) and Wnt inhibitors (Cerberus, Dikkopf).
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| In the mouse embryo, what additional factors are needed for posterior neural fates? | Wnts, Nodals, and FGFs
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| What are the subdivisions of the spinal cord (anterior to post? | Cervical, brachial, thoracic, lumbar, sacral spinal cord.
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| What is the Gastrula Organizer? | It is the center of involution giving rise to the anterior mesendoderm (gives rise to mesoderm and endoderm) and it specifies posterior neural fates as it regresses posteriorly.
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| What are some of the posteriorizing signals expressed by the Gastrula Organizer? | FGF, Nodal, and Wnt
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| Blockage of BMP4 signalling induces what fate? | Anterior neural plate tissue.
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| Blockage of BMP4 signalling with retinoic acid induces what fate? | Posterior neural plate
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Axial Patterning
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| What cluster of genes encode information along the anteroposterior axis of the embryo of insects? | Hox genes
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| How are the Hox genes ordered? | They have the same order as time of development and location within the embryo in insects and mammals.
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| What happens to when Hox genes are mutated? | There are gross axial defects ( eg. duplication or elimination of entire segments and segmental structures).
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| What are the paralogous of Hox genes in mammals? | HoxA-HoxD
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| What cells induce a ventral fate in the spinal cord? | Cells from the notochord
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| What is factor that is secreted by the notochord? | Sonic hedgehog (Shh)
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| What is a morphogen? | A signalling molecule where the concentration produces different cellular responses
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| What cells induce a dorsal fate in the spinal cord? | Cells in the surface ectoderm
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| What does the surface ectoderm secrete to induce dorsoventral patterning along the spinal cord? | BMPs
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| What is the roof plate of the spinal cord induced by the ectoderm to express? | BMP4
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| What will the dorsal most roof plate give rise to? | Both neural cells in the PNS and non-neural structures.
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| What is an example of a specialized cell that are only found in certain locations around the spinal cord? | Specialized motorneurons that are located in the brachial and lumbar regions that innervate limbs.
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| What are the 8 regular structures found in the hindbrain? | rhombomores
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| What happens in the hindbrain if Hoxb-1 is mutated? | Rhombomore 4's motorneurons behave like those in Rhombomore 2 - they do not migrate beyond rhombomore 4 (& even 5) like they do in the wild type.
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| What is the organizing center for the mesencephalon and the metencephalon? | Isthmic Organizer
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| What gene from the Isthmic organizer is critical for specifying the tegmentum and other structures in the mesencephalon (posterior)? | Wnt1
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| What gene from the Isthmic organizer is critical for specifying the cerebellum and other structures in the metencephalon (anterior)? | Fgf8
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| What axis does the Isthmic organizer specify? | Anterior-Posterior
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| The 6 regions of the prosencephalon is called... | Prosomeres
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| What is different about patterning in the prosencephalon? | There are very dramatic cell migrations.
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