Correct option is C
Explanation:
A. A cDNA library was prepared from a lithium chloride-treated amphibian gastrula. The organizer molecule was identified from a clone whose mRNA could rescue the phenotype of a UV-irradiated 1-cell embryo and allow normal development.
This statement is incorrect in the context of the hypothesis being tested. While lithium chloride treatment is known to affect dorsalization, the statement about UV-irradiated embryos and rescue of phenotype does not directly support the functional role of organizer molecules like Noggin. The key point in this hypothesis is the induction of a secondary axis and neural tissue formation, which is not fully explained by the rescue of the phenotype in the UV-irradiated embryos.
B. Clones of cDNA whose mRNA was present in dorsalized but not in ventralized embryos were tested by injecting them into ventral blastomeres and seeing whether they induced a secondary axis.
This statement is correct and directly supports the hypothesis.
The dorsalized embryos have organizer molecules like Noggin, which are essential for the development of the notochord and neural tissue. By injecting mRNA from dorsalized embryos into ventral blastomeres, the experiment tests whether the organizer molecules can induce the formation of a secondary axis, which is a defining feature of the organizer function. This result supports the role of the organizer molecule in axis formation.
C. The molecule, an inhibitor of both Activin and BMPs, caused ectoderm to become neural tissue.
This statement is correct and also supports the hypothesis.
Noggin, which inhibits BMPs, plays a critical role in neural induction. The inhibition of BMPs allows ectodermal cells to develop into neural tissue rather than becoming epidermis. This function is consistent with the role of organizer molecules that promote neural differentiation.
Conclusion:
Statement A is incorrect because the experiment described does not directly test the hypothesis about the organizer molecule's role in inducing a secondary axis or promoting neural differentiation.
Statements B and C are both correct and directly support the hypothesis that organizer molecules like Noggin play a crucial role in secondary axis formation and neural tissue induction.
