Nucleolar-based Dux repression is essential for embryonic two-cell stage exit.

Area of Science:

• Developmental Biology
• Genetics
• Cell Biology

Background:

• Mammalian embryonic development requires a transition from maternal to embryonic gene expression.
• The two-cell (2C) stage in mice involves transient upregulation of MERVL transposons and 2C genes.
• The mechanisms regulating 2C gene expression and subsequent silencing are not fully understood.

Purpose of the Study:

• To investigate the role of nucleolar maturation and ribosomal RNA (rRNA) synthesis in exiting the 2C state.
• To understand how nucleolar function impacts the regulation of MERVL-driven genes and the activator Dux.
• To determine the necessity of nucleolar maturation for embryonic developmental progression.

Main Methods:

• Utilized mouse embryonic stem cells (ESCs) and early mouse embryos.
• Manipulated RNA polymerase I activity to disrupt rRNA synthesis and nucleolar maturation.
• Assessed nucleolar structure, rRNA output, and Dux protein localization.
• Analyzed gene expression patterns and developmental progression.

Main Results:

• Immature nucleoli with reduced rRNA output were observed in 2C-like cells and 2-cell embryos.
• Disruption of nucleolar maturation in ESCs enhanced conversion to a 2C-like state by detaching Dux.
• In embryos, nucleolar disruption led to impaired Dux silencing, failed nucleolar maturation, and arrest at the 2- to 4-cell stage.

Conclusions:

• Robust rRNA synthesis and nucleolar maturation are critical for exiting the 2C developmental stage.
• The nucleolus plays a key role in repressing MERVL-driven transcription, including the Dux activator.
• Proper nucleolar function is essential for successful early mammalian embryonic development.