Cell specific loss of polarity-inducing ability by later stage mouse preimplantation embryos

Area of Science:

• Developmental Biology
• Cell Biology
• Embryology

Background:

• Blastomeres in preimplantation mouse embryos polarize at the 8-cell stage.
• This polarity involves microvilli restriction and membrane changes, induced by asymmetric cell-cell contact.

Purpose of the Study:

• To investigate the capacity of later-stage embryos to induce 8-cell polarization.
• To determine the hierarchy of inducing ability among different embryonic cell types.

Main Methods:

• Isolated nonpolar 8-cell blastomeres were aggregated with various later-stage embryonic components (morulae, inner cell clusters, blastocysts, ICM).
• Aggregates were cultured for 8 hours and then assayed for induced polarity.

Main Results:

• A hierarchy of inducing ability was observed: ICM and inner cell clusters > morula and polar trophectoderm > mural trophectoderm.
• Inducing ability of polar trophectoderm decreased with blastocyst expansion and hatching.

Conclusions:

• The capacity to induce 8-cell blastomere polarization persists in the embryo beyond the 8-cell stage.
• This inductive ability is progressively lost with further cellular differentiation.