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409 exam 2
Terms in this set (11)
Decribe the signal produced by the apical ectodermal ridge (AER) during limb formation
FGF-4 is produced by the apical ectodermal ridge. It stimulates limb growth. When AER is removed, beads coated with FGF-4 still stimulated limb formation.
Describe 3 conventions of the compartment boundary hypothesis.
1. basic unit of growth and compartment boundary hypothesis
2. present in all animals
Name 2 techniques used to observe gene expression in developing tissue
What is the general definition of a morphogen
a chemical that defines the pattern of tissue formation based on a concentration gradient
Where would you expect to see cytonemes in the vertebrate limb and how you would use split GFP to confirm their presence in this tissue?
Cytonemes can be ligand carrier, receptor carriers, or ligand-receptor carriers. Therefore cytonemes would be located at or near cells that aid in limb formation. GFP can be detected and split using antibodies.
You discover a new gene required for formation of the zeugopod; a mutation leads to a missing radius and ulna. (a) describe a technique for detecting the expression of this early gene during limb patterning. Draw and describe how this gene would be expressed if (b) the Early Allocation Model or (c) the Progress Zone Model were true
a. FISH could be used to detect expression of gene during limb patterning by labeling the desired gene and watching it progress. With FISH, the gene would be fluorescent
b. The Early allocation states that cell fate is allocated early and proliferation follows. Mutation would lead to loss of zeugopod. (ZEUOPOD IS LOST)
c. If PZ model were true, the mitoses would be counted and might lead you to believe distal elements are lost. (ZEUGOPOD AND AUTOPOD ARE LOST)
Below is shown the production of clones in normal wild type tissue (top two panels) and engrailed mutant clones.
(a) what do the wild types clones show? (b) what do the engrailed mutant clones show?
c. Why do the engrailed mutant clones respect the boundary when produced in the anterior compartment (lower left panel) but not in the posterior (lower, right)?
a. Wild type shows cells that respect the compartment boundary (due to cell affinity)
b. Engrailed is not necessary in the anterior in order for the cells to respect the compartment boundary. However, in the posterior engrailed is necessary
c. This is because of the cell affinities. Engrailed is only needed to be expressed in the posterior compartment
What is the role of programmed cell death (apoptosis) in limb formation and what would be the effect inhibitor of an apoptosis inhibitor added to a mouse embryo on the articulation of digits in the mouse limb?
Apoptosis is used to eliminate structures that are not needed or in order to make a limb functional, such as chick feet. BMP4 stimulates apoptosis. However in animals, such as ducks, who do not need as much cell death, Gremlin inhibits BMP4 from stimulating apoptosis. Therefore, apoptosis can be regulating depending on the animal. If Gremlin (inhibitor) was injected in a mouse embryo, the digits of the hand and feet would not e diversified. Thus, the mouse would have web-like feet.
Experimental separation of egg longtidually in (A) results in twinned larva, but longitudinally separated at a spot perpendicular (B) results in normal larva and unorganized mass. Why?
The development of dorsal-ventral axis patterning relies on where the sperm enters the egg. In order for normal development, the gray crescent has to be included in both separations. In (A), normal development occurred in both separations because the gray crescent was split in half. In (B), only one separation developed normal because only one blastomere included the gray crescent
You discover a new gene involved in the function of the organizer. Describe how to detect this gene's expression in the organizer and how you could confirm its function, by describing 2 complementary experimental approaches to (1) reduce the gene's function and (2) increase the gene's activity.
If a new gene is discovered in the dorsal blastopore lip, you could detect the expression of the new gene by the injection of a fluorescent dye. The dye would make the gene fluoresceand thus could be detected. You could confirm its function by injecting it into the ventral portion and viewing to see if it forms a second neural tube and dorsal mesoderm. This would mean that the organizer would be properly functioning. In order to reduce the gene function you would need to repress the gene's expression. This could be done by repressor transcription factors. In order to increase the gene function, you would need to enhance gene expression by enhancer transcription factors.
The LMX1 gene is required for dorsal-ventral patterning of the limb. Describe the (a) structure of the gene , (b) where the gene is expressed and (c) the effect of a knockout mutation in the gene in mice and the (e) syndrome associated with a mutation in one copy of the gene in humans.
LMX1 is a gene in the dorsal compartment. Wnt7a in the dorsal activates Lmx1. Lmx1 gene can then activate Shh expression and produce duplicate limbs. If Lmx1 is injected into the ventral portion, dorsal structures will form. A knockout can be formed by injecting blastomeres and breeding until all heterozygots are formed then plating on neomycin. The knockouts cannot properly bind Wnt7a and therefore Lmx1 is not activated resulting in abnormal limb structure. Both copies of Lmx1 have to be present to form a normal structured limb. If haploinsufficiency occurs (only one copy is present).
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