Normal DNA methylation dynamics in DICER1-deficient mouse embryonic stem cells

Area of Science:

• Epigenetics
• Gene Regulation
• Cell Biology

Background:

• Reduced DNA methylation and heterochromatin assembly defects are reported in DICER1-deficient mouse ES cells.
• Previous studies suggested impaired DNA methyltransferase (DNMT) activity or RBL2-mediated repression of DNMT genes.
• Inconsistencies in findings prompted re-evaluation of DNMT activity in these cells.

Purpose of the Study:

• To rigorously test the functional DNA methyltransferase (DNMT) activity in DICER1-deficient mouse ES cells.
• To investigate the role of cell passage number and RNA interference in observed DNA methylation changes.
• To determine if RBL2 protein levels are elevated in DICER1-deficient ES cells.

Main Methods:

• Prolonged culture of Dicer1(-/-) ES cells to assess progressive methylation loss.
• Rebound DNA methylation assay using Cre/loxP conditionally mutant Dicer1 ES cells with Dnmt1 knockdown.
• Western blot analysis to quantify RBL2 protein levels.

Main Results:

• Functional DNMT activity was found to be normal in Dicer1(-/-) ES cells under both prolonged culture and rebound methylation assay conditions.
• RBL2 protein levels were not found to be elevated in Dicer1(-/-) ES cells.
• No evidence of reduced functional DNMT activity as a primary feature of DICER1 deficiency.

Conclusions:

• Reduced functional DNMT activity is not a salient feature of DICER1-deficient ES cells.
• Observed DNA methylation reductions may result from stochastic alterations or dysregulation of opposing pathways.
• siRNA-mediated heterochromatin assembly may not solely depend on DNMT activity in DICER1-deficient cells.