DNMT1 can induce primary germ layer differentiation through de novo DNA methylation

Area of Science:

• Epigenetics
• Developmental Biology
• Genetics

Background:

• DNA methylation and demethylation are crucial for embryonic development, regulated by DNA methyltransferases (DNMTs) and Ten-Eleven Translocation (TET) proteins.
• DNMT1 is primarily known for maintaining DNA methylation post-replication, but its de novo methyltransferase role and broader physiological significance are less understood.

Purpose of the Study:

• To investigate the role of full-length DNMT1 (FL) and a truncated mutant (602) in mouse embryonic stem cell (ESC) differentiation and development.
• To elucidate the de novo methyltransferase capacity of DNMT1 and its impact on epigenetic regulation during early development.

Main Methods:

• Generation of Dnmt1, Dnmt3a, and Dnmt3b triple knockout (Dnmts-TKO) mouse ESCs.
• Complementation of Dnmts-TKO ESCs with full-length DNMT1 (FL) and DNMT1 mutant lacking N-terminus (602).
• Analysis of DNA methylation (5mC) and hydroxymethylation (5hmC) levels, gene expression, and differentiation potential using embryoid body assays.

Main Results:

• Both FL and 602 DNMT1 variants inhibited spontaneous differentiation of Dnmts-TKO ESCs and partially restored DNA methylation and gene expression defects.
• FL DNMT1 promoted global 5mC and 5hmC accumulation during differentiation, while 602 showed asynchronous 5hmC.
• FL DNMT1, unlike 602, effectively drove differentiation towards epiblast-like, mesendodermal, and germline lineages.

Conclusions:

• DNMT1 possesses significant de novo methyltransferase activity crucial for preventing ESC differentiation and promoting germline development.
• The N-terminal region of DNMT1 is critical for its maintenance activity but also contributes to target selectivity and developmental roles.
• DNMT1 plays a multifaceted role in epigenetic regulation extending beyond DNA methylation maintenance, impacting lineage commitment and germline development.