A molecular roadmap of reprogramming somatic cells into iPS cells.

Area of Science:

• Stem cell biology
• Epigenetics
• Molecular biology

Background:

• Factor-induced reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) is a crucial technology but remains inefficient.
• This inefficiency complicates detailed mechanistic studies of the reprogramming process.

Purpose of the Study:

• To investigate defined intermediate cell populations during iPSC generation using genome-wide analyses.
• To elucidate the molecular events and transcriptional dynamics underlying cellular reprogramming.

Main Methods:

• Genome-wide analyses of intermediate cell populations during induced pluripotency.
• Examination of transcriptional waves, epigenetic modifications (bivalent domains, DNA methylation), and factor dependencies.

Main Results:

• Induced pluripotency involves two distinct transcriptional waves: a c-Myc/Klf4-driven first wave and an Oct4/Sox2/Klf4-driven second wave.
• Cells refractory to reprogramming fail to initiate the second wave and can be rescued by co-expression of all four factors.
• Bivalent domain establishment precedes DNA methylation changes, occurring after the second wave during stable pluripotency acquisition.

Conclusions:

• The study identifies key genes acting as roadblocks and potential surface markers for enriching cells prone to iPSC formation.
• Provides novel mechanistic insights into the sequential molecular events governing cellular reprogramming.