Successful compaction from morula to blastula involves:
Compaction to form morula requires establishment of strong cell-cell adhesion mediated by E-cadherin, a calcium-dependent adhesion molecule. Extracellular calcium rigidifies cadherin repeats enabling trans-homophilic binding between blastomeres, intracellularly binding beta-catenin which links to alpha-catenin and actin cytoskeleton. Activation and clustering of this cadherin-catenin complex drives blastomere flattening, polarization, tighter apposition and induction of tight junction formation. Blockage of cadherin or removal of calcium prevents compaction, while calcium ionophores alone without cadherin function insufficient. Successful compaction therefore depends on coordinated calcium influx and functional cadherin-beta-catenin assembly orchestrating Hippo pathway mediated lineage segregation.
Ref: Maître JL et al., Nature Cell Biology 2015: E-cadherin beta-catenin regulation of compaction and Hippo mediated cell fate.