Pcgf5 controls the exit from totipotency in mouse embryonic stem cells

Area of Science:

• Developmental Biology
• Stem Cell Biology
• Epigenetics

Background:

• Mouse embryonic stem cells (ESCs) possess a rare subpopulation of two-cell-like cells (2CLCs) that mimic early embryonic totipotency.
• These 2CLCs transiently reactivate zygotic genome activation (ZGA) markers like MERVL and Zscan4.
• Polycomb repressive complex 1 (PRC1) and Pcgf6 are known to restrict entry into the 2CLC state, but exit factors are unclear.

Purpose of the Study:

• To identify factors controlling exit from the 2CLC state and loss of totipotency in mouse ESCs.
• To investigate the role of Pcgf paralogs, particularly Pcgf5, in regulating the 2CLC state dynamics.

Main Methods:

• Utilized a reporter ESC line (MtZG) tracking MERVL and Zscan4c expression.
• Manipulated Pcgf5 dosage using doxycycline-inducible overexpression (OE) and CRISPR-mediated knockout (KO).
• Employed time-lapse imaging to directly observe the duration of the 2CLC state.

Main Results:

• Pcgf5 is significantly upregulated in 2CLCs and forms a chimeric transcript during ZGA.
• Pcgf5 overexpression reduced the 2CLC population, shortening their state duration.
• Pcgf5 knockout increased the 2CLC population, prolonging their state duration.

Conclusions:

• Pcgf5 acts as a crucial regulator controlling exit from the totipotent-like 2CLC state in mouse ESCs.
• This study reveals a Polycomb group factor's dual role in both entry and exit dynamics of the 2CLC state.
• Findings shed light on the epigenetic mechanisms governing pluripotency and totipotency transitions in early development.