ERK2 suppresses self-renewal capacity of embryonic stem cells, but is not required for multi-lineage commitment

Area of Science:

• Cell Biology
• Developmental Biology
• Stem Cell Biology

Background:

• The Fibroblast Growth Factor-Extracellular signal-Regulated Kinase (FGF-ERK) pathway is crucial for mouse embryonic stem cells (ESCs) to exit self-renewal and differentiate.
• ERK1 and ERK2 are the main isoforms of ERK, with ERK2 being predominant in ESCs.

Purpose of the Study:

• To investigate the specific role of Erk2 in ESC self-renewal and differentiation.
• To determine if ERK1 can compensate for the loss of ERK2 function in ESCs.

Main Methods:

• Genetic ablation of Erk2 in mouse ESCs.
• Analysis of ERK activity via substrate phosphorylation and immediate-early gene (IEG) induction.
• Assessment of lineage specification through embryoid body formation and neural induction.
• Quantification of pluripotency gene expression (Nanog, Tbx3) and Nanog-GFP heterogeneity.
• Colony forming assays to evaluate self-renewal capacity.
• Rescue experiments using transgenic expression of ERK1 or ERK2.

Main Results:

• Erk2-null ESCs showed hyper-phosphorylation of ERK1 but reduced overall ERK activity.
• Transgenic expression of ERK1 or ERK2 rescued normal induction of ERK targets and p90RSK phosphorylation, indicating functional redundancy.
• Erk2-null ESCs did not exhibit defects in germ layer specification.
• Under self-renewal conditions, Erk2-null ESCs displayed increased Nanog and Tbx3 expression, reduced Nanog-GFP heterogeneity, and enhanced self-renewal.
• Transgenic add-back of ERK2 restored normal pluripotent gene expression and self-renewal capacity.

Conclusions:

• ERK2 destabilizes ESC self-renewal by downregulating pluripotency genes like Nanog.
• ERK2 is not essential for the initial stages of germ layer specification in mouse ESCs.
• While ERK1 can partially compensate for ERK2, ERK2 plays a significant role in maintaining ESC pluripotency and regulating self-renewal dynamics.