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#morula compaction

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Fertilization in mammals-lll

Ion critical for morula compaction:

Morula compaction depends on extracellular divalent cation calcium enabling functional conformation of E-cadherin adhesion molecules. Calcium binding rigidifies extracellular cadherin repeats facilitating trans-interaction between neighboring blastomeres, initiating formation of adherens junctions and recruitment of catenins to cortical actin. Chelation by EDTA or EGTA rapidly decompacts embryos, reversibly. Potassium, sodium or magnesium cannot substitute for calcium in this homophilic adhesion. Calcium influx also participates in downstream signaling for polarization including activation of protein kinase C, establishing apical-basal polarity. Thus calcium is irreplaceable ionic cofactor ensuring stable inter-blastomere adhesion during transition from loose cleavage stage to compact morula.

Ref: Ducibella et al., Dev Biol 1977: Calcium dependence of compaction and desmosome formation in mouse morula.

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Fertilization in mammals-lll

Protein complex essential for morula compaction:

Compaction of eight-cell morula into tightly adherent structure critical for blastocyst formation relies on calcium-dependent adhesion complex E-cadherin, beta-catenin, alpha-catenin and actin. Homophilic E-cadherin bonds stabilize blastomere contacts, intracellularly recruiting beta-catenin which anchors to cytoskeleton enabling polarization, increased compaction and sealing. This complex activates downstream Hippo signaling distinctions between inside and outside cells. Actin-myosin contractility participates downstream, but tubulin-kinesin or dynactin complexes are not primary drivers. Genetic ablation of E-cadherin or beta-catenin prevents compaction leading to embryonic lethality, highlighting cadherin-catenin complex as essential architectural organizer of early mammalian morphogenesis and lineage segregation.

Ref: Stephenson et al., Development 2010: Cadherin-catenin complex essential for morula compaction and cell polarity.

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