In amphibians and fish, the cells of the organizer ultimately contribute to i) pharyngeal endoderm, ii) head mesoderm, iii) dorsal mesoderm, and iv) dorsal blastopore lip. The following statements are made about the function of the organizer and its derivatives:
A. The pharyngeal endoderm and pre-chordal plate prevent formation of forebrain and midbrain.
B. The organizer has the ability to dorsalize the ectoderm and induce formation of the neural tube.
C. The dorsal mesoderm inhibits induction of the hindbrain and trunk.
D. The organizer tissue possesses the ability to dorsalize the surrounding mesoderm into somite-forming mesoderm.
Which one of the following options is a combination of all correct statements?

Correct option is B

Correct Answer
Option (b): B and D only
Explanation:
The organizer (Spemann–Mangold organizer) secretes signaling molecules that dorsalize the ectoderm, leading to neural induction and neural tube formation, making statement B correct. It also dorsalizes surrounding mesoderm to form somites, supporting statement D. Statements A and C contradict known organizer functions.
Information Booster
· The organizer functions primarily by inhibiting BMP signaling through molecules such as chordin, noggin, and follistatin.
· BMP inhibition permits ectoderm to adopt a neural fate instead of an epidermal one.
· Organizer-derived tissues are essential for body axis formation and correct nervous system regionalization.
Additional Knowledge (Incorrect Options Explained)
Statement A is incorrect because the pharyngeal endoderm and prechordal plate promote, not prevent, forebrain and midbrain development.
Statement C is incorrect because dorsal mesoderm induces the formation of hindbrain and trunk structures rather than inhibiting them.