Early-stage epigenetic modification during somatic cell reprogramming by Parp1 and Tet2

Area of Science:

• Epigenetics
• Stem Cell Biology
• Molecular Biology

Background:

• Somatic cell reprogramming into induced pluripotent stem cells (iPSCs) involves erasing somatic epigenetic signatures and establishing embryonic stem cell (ESC) epigenetic marks.
• The pluripotency factors Oct4, Sox2, Klf4, and c-Myc (OSKM) drive this reprogramming process.
• Early epigenetic events preceding pluripotency gene transcription are critical but not fully understood.

Purpose of the Study:

• To investigate the roles of epigenetic modification factors in the early stages of somatic cell reprogramming.
• To elucidate the specific functions of poly(ADP-ribose) polymerase-1 (Parp1) and ten-eleven translocation-2 (Tet2) in establishing early epigenetic marks.
• To determine if 5-hydroxymethylcytosine (5hmC) acts as a distinct epigenetic mark during reprogramming.

Main Methods:

• Utilized OSKM transduction to induce somatic cell reprogramming.
• Analyzed the recruitment of Parp1 and Tet2 to pluripotency loci (Nanog, Esrrb) by day 4.
• Assessed the roles of Parp1 and Tet2 in regulating DNA methylation (5mC) and hydroxymethylation (5hmC).
• Examined histone modifications and chromatin accessibility at pluripotency loci.

Main Results:

• Parp1 and Tet2 were recruited to Nanog and Esrrb loci by day 4 of OSKM reprogramming.
• Parp1 regulated 5-methylcytosine (5mC) modification, while Tet2 was essential for 5-hydroxymethylcytosine (5hmC) generation.
• Evidence suggests 5hmC functions as a distinct epigenetic mark, not just a demethylation intermediate.
• Both Parp1 and Tet2 were required for establishing active chromatin marks at pluripotency loci.
• Parp1 enhanced Oct4 accessibility, further promoting reprogramming.

Conclusions:

• Parp1 and Tet2 play complementary and essential roles in the early epigenetic reprogramming of somatic cells.
• These factors initiate an epigenetic program involving distinct 5mC and 5hmC marks, facilitating subsequent transcriptional activation of pluripotency genes.
• The findings highlight the importance of Parp1 and Tet2 in establishing an ESC-like epigenetic state during iPSC generation.