Fgf8 expression in the anterior developing mouse brain induces anterior identity marker expression (anteriorization). The Fgf8 receptor is uniformly expressed in the brain. Which one of the following experiments best demonstrates this fact?

Correct option is A

Explanation:

Let’s analyze each option based on the experimental setup described in the question:

• Statement 1: Transgenic overexpression of Fgf8 in the posterior of the developing mouse brain causes anteriorization at both ends of the brain.

  • This is correct. The key factor here is that Fgf8 expression in the anterior part of the developing brain induces anteriorization. The fact that Fgf8 overexpression in the posterior of the developing brain can cause anteriorization at both ends of the brain shows that Fgf8 can induce anterior identity at both the anterior and posterior ends of the developing brain. This is consistent with the uniform expression of the Fgf8 receptor and the action of Fgf8 in anteriorizing both ends.

• Statement 2: Transgenic overexpression of Fgf8 receptor in the posterior of the developing mouse brain causes anteriorization at both ends of the brain.

  • This is incorrect. Overexpression of Fgf8 receptor might enhance the response to Fgf8 signaling, but the experiment specifically addresses the Fgf8 expression in the brain. Fgf8 expression (not the receptor) in the posterior is what leads to anteriorization, so this statement is not entirely accurate in demonstrating the fact as per the question.

• Statement 3: Grafting the anterior portion of an Fgf8 null developing mouse brain into the posterior of another developing mouse brain causes the recipient's brain to be anteriorized at both ends.

  • This is incorrect. While the grafting experiment may demonstrate that Fgf8 is involved in anteriorization, this does not directly show that Fgf8 itself induces anteriorization in a uniform receptor-expressing brain. The result could involve other factors that might be operating during the grafting process and might not conclusively demonstrate the role of Fgf8 expression as stated in the question.

• Statement 4: Transgenic overexpression of Fgf8 in the posterior of the developing mouse brain results in no anteriorization.

  • This is incorrect. Based on what was described in Statement 1, Fgf8 overexpression in the posterior does indeed result in anteriorization. Therefore, this statement contradicts the fact described in the question.