Correct option is C
Explanation-
β-catenin is a transcriptional coactivator. In sea urchin development, β-catenin is crucial for specifying endoderm and mesoderm. Normally, β-catenin accumulates only in micromeres (small cells at the vegetal pole). On the other hand, GSK-3 promotes degradation of β-catenin. When GSK-3 is active, β-catenin levels are low in other cells (except micromeres). Micromeres escape this degradation, so β-catenin builds up and drives endomesodermal fate.
If GSK-3 is blocked then GSK-3 can't degrade β-catenin, therefore, β-catenin accumulates in all cells, not just micromeres. This causes animal cells (which normally become ectoderm) to mis-specify as endoderm and mesoderm.
Incorrect options-
Option a: "β-catenin accumulation in the nuclei of large micromeres will be inhibited leading to formation of ectodermal ball."
If GSK-3 is blocked, β-catenin is stabilized, not inhibited. This means accumulation increases, not decreases. Also, large micromeres are not the primary β-catenin-rich cells—small micromeres are. Forming only ectoderm (an ectodermal ball) would require β-catenin to be absent, not present.
Option b : "β-catenin will accumulate in the nuclei of all blastula cells leading to an ectodermal ball."
β-catenin accumulation promotes endoderm and mesoderm, not ectoderm. If β-catenin is in all cells, ectoderm fate is suppressed. The embryo would not form an ectodermal ball; it would form an endoderm/mesoderm-dominant structure.
Option d: "β-catenin will accumulate in the nuclei of large micromeres will be inhibited leading to animal cells getting specified as endoderm and mesoderm."
This option is self-contradictory: It first says β-catenin will be inhibited in micromeres. Then it says animal cells will become endoderm and mesoderm (which requires high β-catenin). If β-catenin is inhibited, endoderm/mesoderm cannot form.
But blocking GSK-3 actually leads to β-catenin accumulation, not inhibition.
So, the correct answer is option c - β-catenin will accumulate in the nuclei of all blastula cells leading to animal cells getting specified as endoderm and mesoderm.
