Context-Dependent Requirement of Euchromatic Histone Methyltransferase Activity during Reprogramming to Pluripotency

Area of Science:

• Epigenetics
• Stem Cell Biology
• Cellular Reprogramming

Background:

• Histone methylation, specifically H3K9 methylation, acts as a barrier to cellular reprogramming.
• Ascorbic acid (AA) can facilitate induced pluripotent stem cell (iPSC) derivation by interfering with methyltransferases or activating demethylases.
• The interplay between specific methyltransferases and AA during reprogramming is not fully understood.

Purpose of the Study:

• To investigate the role of EHMT1 and EHMT2 methyltransferases in AA-enhanced cellular reprogramming.
• To elucidate the impact of EHMT inhibition on H3K9 methylation dynamics and reprogramming efficiency.
• To assess the developmental potential of iPSCs generated under conditions of EHMT inhibition.

Main Methods:

• Utilized an enhanced reprogramming system with ascorbic acid (AA).
• Applied chemical inhibition of EHMT1 and EHMT2 methyltransferases.
• Analyzed H3K9 dimethylation levels, somatic gene downregulation, and mesenchymal-to-epithelial transition (MET).
• Evaluated the developmental competence of derived iPSCs through blastocyst injection.

Main Results:

• EHMT1/2 inhibition counteracted iPSC formation in the presence of AA, an effect dependent on EHMT1.
• EHMT inhibition led to rapid loss of H3K9 dimethylation, impaired somatic gene silencing, and failed MET.
• Transient EHMT inhibition resulted in iPSCs with compromised developmental potential, evidenced by failed mouse development after blastocyst injection.

Conclusions:

• EHMT1 and EHMT2 play critical roles in supporting efficient and error-free iPSC reprogramming.
• A balanced interplay between AA-stimulated enzymes and EHMT activity is essential for successful reprogramming to pluripotency.
• Disruption of H3K9 methylation dynamics via EHMT inhibition impacts both reprogramming efficiency and the pluripotency of derived cells.