Asynchronous mouse embryo polarization leads to heterogeneity in cell fate specification

Area of Science:

• Developmental biology
• Cell biology
• Embryogenesis

Background:

• The initial lineage segregation in mammalian embryos differentiates the inner cell mass (ICM) from the trophectoderm (TE).
• This process involves cell polarization and asymmetric cell divisions at the 8-cell stage, establishing distinct cell fates.

Purpose of the Study:

• To investigate the asynchronous nature of embryo polarization during early development.
• To elucidate the molecular mechanisms linking early cell asymmetries to subsequent lineage specification.

Main Methods:

• Analysis of cell polarization timing and molecular profiles at the 8-cell stage in mouse and human embryos.
• Investigating the role of CARM1 activity and its substrate BAF155 in early lineage allocation.

Main Results:

• Embryo polarization is asynchronous, with cells polarizing at different times during the 8-cell stage exhibiting distinct properties.
• Early polarizing cells are biased towards trophectoderm (TE) lineage specification.
• Reduced CARM1 activity at the 4-cell stage is linked to increased BAF155 and promotes early polarization and TE fate.

Conclusions:

• Asynchronous polarization at the 8-cell stage contributes to the first lineage allocation.
• A molecular link is established between 4-cell stage asymmetries (CARM1/BAF155) and 8-cell stage polarization, influencing TE specification.