17. The signaling molecule Wnt (a relative of Wingless) activates gene pathway b
ID: 218610 • Letter: 1
Question
17. The signaling molecule Wnt (a relative of Wingless) activates gene pathway below. It is involved in regulating stem cell pluripotency in expression via the signal transduction vertebrates Gene t-expres (a) Using the pathway above, explain how in wildtype animals, the presence of Wnt leads to gene expression (2 pts) (b) The gsk3 kinase inactivates the beta-catenin (B-cat) protein by phosphorylating it. You identify a missense mutation in the ?-catenin gene that removes the phosphorylation site, but has no other effect on ?-catenin function. What effect would you expect to observe on gene expression in this mutant, in both the presence and absence of Wnt? Briefly explain. (3 pts) (c) You identify another mutation in the f-catenin gene, this time introducing an early stop codon that complete eliminates the function of the B-catenin gene. What effect would you expect to observe on gene expression in this mutant, in both the presence and absence of Wnt? Briefly explain. (3 pts) Almost there... one more question...Explanation / Answer
Wnt activates Frz, which activates dsh. dsh inhibits gsk3. gsk3 inhibits beta-catenin. Beta-catenin leads to gene expression.
a) Wnt activates Frz, which in turn activates dsh. dsh would inhibit gsk3. Since there is an absence of active gsk3, beta-catenin is not inhibited. The beta-catenin leads to gene expression.
b) If there is a missense mutation in the beta-catenin that removes the phosphorylation site, the gsk3 kinase would not be able to phosphorylate the beta-catenin. This would mean that the beta-catenin would not be inactivated and it would be constitutively active, even in the presence of active gsk3. The constitutively active beta-catenin would lead to gene expression regardless of the presence or absence of upstream signalling molecules (Wnt, Frz, dsh, gsk3) in the pathway. In the presence or absence of Wnt, the result would be gene expression. In the presence of Wnt, gsk3 would be inactivated and would not be able to act on beta-catenin due to this inactivation. In the absence of Wnt, gsk3 would be active, yet it would not be able to phosphorylate the beta-catenin to inactivate it due to the absence of the phosphorylation site. In both cases, the beta-catenin would be active and would lead to gene expression.
c) Due to this mutation, the beta-catenin has lost it's function. Since it has lost it's function, activation or inactivation of beta-catenin would not result in gene expression. Regardless of it's active or inactive state, beta-catenin has lost it's ability to induce gene expression. In the presence of Wnt, beta-catenin would be active, but since it has lost it's function, it would not be able to induce gene expression. In the absence of Wnt, beta-catenin would be inactivated, and it would not induce gene expression.
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