Question

Question 3: Diagnose a novel set of signal transduction pathways (8 pts)

You isolate cells from the brain of a mouse, and work to characterize them. In your first experiments you grow your cells in a petri dish, and add various signals to the petri dish and determine how the cells respond. You get the following information. Assume there are no other genes or signals beyond what is mentioned.

Hint: sometimes it helps to sketch the signal pathways first, and then answer the questions. But use whatever strategy works for you!

Signal Response

Signal 1 only Gene 1 is expressed

Signal 2 only No change in gene expression

Signal 3 only No change in gene expression

Signal 1 + 2 Gene 1 is expressed briefly and then stops

Signal 2 + 3 No change in gene expression

Signal 1 + 3 Gene 1 and Gene 2 are expressed

Given the information above, what can you say about this system? For A through C, determine whether you agree with the statement or not and explain your answer. For part D, pick the best answer from the choices given and explain why you think it’s the best answer.

A. Signal 1 leads to the binding of a TF to the DNA of Gene 1

B. Two different signaling pathways are required for expression of Gene 2

C. The Signal 2 pathway is non-functional in this cell

D. If you were to do another experiment and expose the cell to all three signals, what would happen? (pick one from the choices below and explain your answer)

i. Gene 1 expression only

ii. Gene 2 expression only

iii. Gene 1 and Gene 2 expressed initially, followed by only Gene 1 expression

iv. Gene 1 and Gene 2 expressed initially, followed by only Gene 2 expression

v. Gene 1 and Gene 2 are expressed continuously

Answer 1

A) In this one we must agree, as the sole presence of signal 1 induces the expression of gene 1, this signal might be initiating transcription of such gene

B) This one is true, gene 2 is only expresses when both signals 1 and 3 are applied

C) Wrong, signal 2 seems to inhibit gene 1 expression, because when gene 1 is expressing (due to signal 1), signal 2 presence rapidly stops gene 1 expression

D) iv. Gene 1 and gene 2 expressed initially, followed by only gene 2 expression. This would occur because the signals 1 and 3 activate genes 1 and 2, but then signal 2 stops gene 1 and only gene 2 remains.