Totipotency and high plasticity in an embryo with an invariant, fate-specifying cleavage program

Area of Science:

• Developmental biology
• Cellular plasticity
• Evolution of development

Background:

• Animal embryos transition from totipotent zygotes to cells with restricted fates.
• The timing of totipotency loss and fate specification varies significantly across species.
• Invariant cleavage programs, common in nematodes, typically involve early cell fate restriction.

Purpose of the Study:

• To investigate the developmental plasticity of the acoel Hofstenia miamia, which exhibits an invariant cleavage program.
• To determine if blastomeres in H. miamia embryos retain totipotency and plasticity despite asymmetric cleavages.

Main Methods:

• Blastomere isolation assays at the 4-cell stage.
• Photoconversion-based lineage tracing.
• Embryo reconstitution assays at the 8-cell stage.

Main Results:

• Single macromeres from 4-cell stage H. miamia embryos were totipotent, forming complete organisms.
• Lineage tracing demonstrated that blastomeres could generate tissues not normally produced by them.
• All blastomeres from 8-cell stage embryos could be reprogrammed, indicating high plasticity.

Conclusions:

• Hofstenia miamia embryos display unexpected post-zygotic totipotency and high blastomere plasticity, even with an invariant cleavage program.
• These findings challenge the correlation between invariant cleavage and early fate restriction.
• The developed assays make H. miamia a valuable model for studying the mechanisms of extended developmental plasticity.