Question

Explain the following observation. Be specific in your answer.

1. Injection of excess beta-catenin into the ventral side of an oocyte, causes a second axis to form.

Answer 1

Injection of excess beta-catenin into the ventral side of an oocyte, causes a second axis to form.

Explanation: β-catenin is a multifunctional protein that can act as a nuclear transcription factor or an anchor for cell membrane cadherins. In Xenopus embryos, β-catenin begins to accumulate in the dorsal region of the egg during the cytoplasmic movements of fertilization. β-catenin continues to accumulate preferentially at the dorsal side throughout early cleavage and this accumulation is seen in the nuclei of the dorsal cells. β-catenin, a cytoplasmic cadherin-associated protein required for cadherin adhesive function is necessary for forming the dorsal axis. The injection of excess β-catenin into the ventral side of the embryo produces a secondary axis by overexpression of β-catenin the early Xenopus embryo.  This region interacts with C-cadherin and with the APC tumor suppressor protein that requires the amino-terminal region of beta-catenin to bind to the complex. Since alpha-catenin is required for cadherin-mediated adhesion, for example the armadillo repeat region alone probably cannot promote cell adhesion, making it unlikely that beta-catenin induces axis duplication by increasing cell adhesion.