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30 Cards in this Set
- Front
- Back
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What is Accutane?
What is it used for? What can it cause during development? |
Oral retinoic acid
Used for the treatment of acne and acute promyelocytic leukemia Can cause a wide range of birth defects by interfering with Hox gene expression |
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What can defective shh signaling cause?
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Holoprosencephaly
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Describe the mechanism of heart induction
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The heart requires mesoderm (tissue of origin), endoderm, and the node.
The node secretes nodal (BMP) Endoderm secretes a wnt inhibitor (Dickkopf-1) |
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Describe neural plate induction
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The neural plate produces a neural plate inhibitor called BMP-4
Both noggin and chordin are produced by the node and mesoderm Noggin and chordin are inhibitors or BMP-4, inhibiting the inhibitor of neural plate formation, leading to its formation |
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Where are Hox genes expressed first?
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Posterior of the embryo
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What causes the splitting of the brain into segments? (forebrain, midbrain, hindbrain)
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The expression of Hox genes
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From where is retinoic acid first expressed in the embryo?
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The node
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How many Hox genes are there and how many copies?
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13 genes and four copies (A-D)
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What do the Hox genes code for?
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Transcription factors that regulate the expression of other genes
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Where would HoxB 13 be expressed?
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In the posterior of the embryo
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Where would HoxD 2 be expressed?
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Towards the anterior of the embryo
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The limits of Hox gene expression forms what?
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The margins of somites
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If Hox 6 expression causes C4 to be made, what happens if Hox 5 is knocked out?
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C4 is produced again
Knocking out a Hox gene causes the more anterior structure to be repeated |
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If Hox 6 normally causes C4 to be produced, what happens if Hox 5 is overexpressed?
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C4 instead becomes C5; becomes more posterior
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Do Hox genes expressed in the anterior have high or low sensitivity to retinoic acid?
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High sensitivity
(only those with very high sensitivity can express at low concentrations of RA) |
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True or false:
More Hox genes are expressed in the posterior than the anterior |
True
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What is a possible reason for the four sets of Hox genes?
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Because they are so important in development, having 3-4 copies of a gene provides redundancy and resistance to mutation; only require one copy to function
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What induces the floorplate in the neural tube?
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High concentrations of shh secreted by the notochord.
Low concentrations produce motor neurons in the basal plates |
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From what does the limb bud derive?
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Somatopleure
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From what does the apical ectodermal ridge (AER) form? What is its orientation?
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Arises from the surface ectoderm of the limb bud and is a thickening that runs along the anterior / posterior axis
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Describe the zone of polarizing activity (ZPA) of the limb bud
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The ZPA is located in the posterior of the limb bud
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Describe induction of the limb bud
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The Hox code causes the intermediate mesoderm to produce FGF-10, which induces the formation of limbs on the adjacent lateral plate mesoderm
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Describe the action of the AER
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Secretes FGF-4 and 8, which patterns the proximal-distal axis of the limb (humerus, radius, ulna)
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What differentiates forelimb from hindlimb?
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Hox patterning causes Tbx5 expression only in the forelimb, and Tbx4 only in the hindlimb
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Describe the ZPA
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Located in the posterior of the limb bud
High levels of shh leads to posterior structures like the ulna and pinkie, low levels leads to thumb and radius |
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How is the dorsal/ventral axis of the limbs determined?
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Dorsal ectoderm secretes Wnt-7a Paws v. back of hands
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What are the mediators of the different axes of the limbs?
Proximal / distal Dorsal / ventral Posterior / anteroir |
Prox / distal = FGF-4 and 8 from AER
Dorsal / ventral = Wnt-7a from dorsal ectoderm Posterior / anterior = shh from ZPA in posterior mesoderm |
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Explain how Hox genes pattern proximal / distal axis of limbs
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Hox 9 through 13 is expressed in the distal region of the limb bud, and the anterior only expresses Hox 9
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What leads to apoptosis of webbing between digits?
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Expression of BMP-4
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What causes webbing disorders?
(Syndactyly) |
Lack of BMP-4 expression or action
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