The cadherin catenin complex is extremely important during compaction from a morula to the blastula. Transition of early embryonic cells into a blastula differed depending on the presence or absence of calcium ions. In addition, an investigator blocked the expression of β-catenin using in vivo morpholinos to detect its effect simultaneously on compaction. Which one of the following conditions will lead to the most successful transition of the morula into the blastula?​

Correct option is D

Explanation:

• Statement 1: The blastula will continue to develop even when calcium ions are absent, since β-catenin will get activated automatically by cadherins.

  • This is incorrect. Calcium ions are crucial for the proper functioning of cadherins in cell adhesion. Without calcium, cadherins cannot function effectively, and β-catenin activation will be impaired. Therefore, the development of the blastula would be hindered without the presence of calcium.

• Statement 2: In the absence of calcium ions, calcium ionophores will assist development even when vivo morpholinos to β-catenin are introduced.

  • This is incorrect. Calcium ionophores allow calcium to enter cells, but β-catenin is still important in the process. Blocking β-catenin with morpholinos would still prevent proper development, even with the introduction of calcium ionophores. The role of β-catenin cannot be fully bypassed just by adding calcium ions.

• Statement 3: Presence of calcium ions will enhance development when vivo morpholinos to cadherins have been introduced to the early embryo.

  • This is incorrect. Morpholinos to cadherins would inhibit the function of cadherins, regardless of the presence of calcium ions. Cadherins are essential for proper cell-cell adhesion, and even in the presence of calcium, if cadherin function is blocked, compaction and blastula formation will be impaired.

• Statement 4: Presence of calcium ions is essential for activation of cadherin and β-catenin, so that actin gets mobilized and compaction ensues.

  • This is correct. Calcium ions are essential for cadherin function, and the activation of cadherins enables the β-catenin complex to associate with the actin cytoskeleton, triggering compaction and blastula formation. This is the most complete description of how calcium ions and β-catenin work together to support the transition from morula to blastula.