If planaria is cut in transverse, active Wnt signaling in the posterior side of the head piece is essential for the regeneration of a tail. Students were investigating the role of gene abc in this process. They find that overexpressing abc in the head piece blocks tail regeneration. However, overexpressing constitutively active β-catenin along with abc in the severed head piece allows tail formation.

Which one of the following pathways correctly depicts the role of abc and β-catenin in planarain tail regeneration?

Correct option is A

Interpretation from question:

1. Wnt signaling is essential for tail regeneration.

2. Overexpressing gene abc blocks tail regeneration.

3. But if we overexpress active β-catenin along with  abc, tail regeneration happens.

This means that:

1. If overexpressing abc blocks tail regeneration, abc must inhibit some part of the tail regeneration pathway.

2. If active β-catenin can rescue tail regeneration even in the presence of abc, then:

   • abc acts upstream of β-catenin

   • abc likely blocks Wnt or prevents β-catenin activation

Option 1  is correct :  because only this option satisfying the above condition.

In this interpretation:

• Normal levels of abc: promote Wnt → β-catenin → tail regeneration

• Overexpression of abc: disturbs the pathway (maybe inhibitory at high levels)

• Adding active β-catenin bypasses the block → confirms abc acts upstream