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Updated: Jan 10, 2026

Initiating Differentiation in Immortalized Multipotent Otic Progenitor Cells
Published on: January 2, 2016
Inactivation of CDK4/6, CDK2, and ERK in G1-phase triggers differentiation commitment
Sanjeev Sharma1, Henri Berger1, Tobias Meyer1,2
1Department of Biochemistry & Biophysics, Weill Cornell Medicine/Cornell University, New York, NY, USA.
Abstract:
Terminal cell differentiation, a process vital for tissue development and regeneration where progenitor cells acquire specialized functions and permanently exit the cell cycle, remains poorly understood at the molecular level. Using live-cell imaging and adipogenesis as a model, we show that the initial stage involves a variable number of cell divisions, driven by redundant CDK4/6 or CDK2 activation. Afterwards, a delayed decrease in cyclin D1 and an increase in p27 levels reduce CDK4/6 and CDK2 activity. This results in G1 lengthening and the induction of PPARG, the master regulator of adipogenesis. PPARG then induces p21, and later p18, ultimately causing irreversible inactivation of CDK4/6 and CDK2, and thus, permanent cell cycle exit. However, contrary to expectation, CDK inactivation alone is not sufficient to trigger differentiation commitment; ERK inactivation is also necessary. Our study reveals that the coordinated activation and subsequent delayed inactivation of CDK4/6, CDK2, and ERK are crucial for irreversible cell cycle exit and differentiation commitment in terminal cell differentiation.
Insights
Terminal cell differentiation requires coordinated CDK and ERK pathway inactivation. This study reveals that cell cycle exit and differentiation commitment depend on the precise timing of these molecular events.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Terminal cell differentiation is crucial for tissue development and regeneration.
- The molecular mechanisms underlying permanent cell cycle exit remain incompletely understood.
Purpose of the Study:
- To elucidate the molecular events governing terminal cell differentiation and cell cycle exit.
- To identify the key signaling pathways and their temporal regulation during differentiation commitment.
Main Methods:
- Live-cell imaging of adipogenesis as a model system.
- Analysis of cell cycle regulators (CDK4/6, CDK2, cyclins, p27, p21, p18) and ERK pathway activity.
- Investigating the role of CDK and ERK inactivation in differentiation commitment.
Main Results:
- Initial cell divisions are driven by CDK4/6 or CDK2 activation.
- Delayed inactivation of CDK4/6 and CDK2, alongside cyclin D1 decrease and p27 increase, lengthens G1 phase and induces PPARG.
- ERK inactivation is essential, in addition to CDK inactivation, for irreversible cell cycle exit and differentiation commitment.
Conclusions:
- Coordinated activation and delayed inactivation of CDK4/6, CDK2, and ERK are critical for terminal cell differentiation.
- Differentiation commitment is a multi-step process involving precise temporal regulation of cell cycle regulators and signaling pathways.
- This study provides novel molecular insights into the regulation of cell cycle exit and differentiation.
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