Correct option is B
Explanation-
In Xenopus embryos, proper development of dorsal structures (e.g., notochord, neural tube) requires inhibition of BMP (Bone Morphogenetic Protein) signaling, which otherwise promotes ventral fates.
Noggin is a BMP inhibitor - It binds directly to BMPs (like BMP4), preventing them from interacting with their receptors. This inhibition promotes dorsal cell fates. When injected into ventralized embryos (embryos exposed to high BMP and lacking dorsal features), Noggin mRNA can rescue the formation of dorsal structures.
Incorrect options -
Option A – Beta-catenin
It involved in Wnt signaling, and helps initiate dorsal development early. While important, it’s not a BMP inhibitor, and doesn't directly rescue dorsal structures in ventralized embryos via BMP inhibition.
Option C – Disheveled
This also part of the Wnt signaling pathway. It stabilizes beta-catenin by inhibiting GSK3 but does not inhibit BMP signaling.
Option D – Siamois
A transcription factor activated by beta-catenin. It is important for organizer formation but not a direct BMP inhibitor; its expression occurs downstream of Wnt signaling.
So, the correct answer is option B - Noggin.
