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Related Experiment Video

Updated: May 12, 2026

Live Cell Imaging with Time Lapse Photography to Study Epidermal Keratinocyte Proliferation Kinetics

Live Cell Imaging with Time Lapse Photography to Study Epidermal Keratinocyte Proliferation Kinetics

Published on: June 6, 2025

Actin filament dynamics impacts keratinocyte stem cell maintenance.

Daisuke Nanba¹, Fujio Toki, Natsuki Matsushita

¹Laboratory of Stem Cell Dynamics, Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne, Switzerland. nanba8@m.ehime-u.ac.jp

EMBO Molecular Medicine

|April 5, 2013

Summary

Stem cell cultures lose growth potential through clonal conversion, linked to changes in actin organization and response to epidermal growth factor (EGF). Rac1 inhibition drives this stem cell loss.

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Last Updated: May 12, 2026

Live Cell Imaging with Time Lapse Photography to Study Epidermal Keratinocyte Proliferation Kinetics

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Establishing a High Throughput Epidermal Spheroid Culture System to Model Keratinocyte Stem Cell Plasticity

Establishing a High Throughput Epidermal Spheroid Culture System to Model Keratinocyte Stem Cell Plasticity

Published on: January 30, 2021

Area of Science:

Cell Biology
Regenerative Medicine
Stem Cell Biology

Background:

Cultured human epidermal keratinocyte stem cells (holoclones) are vital for regenerative medicine.
Holoclones lose proliferative capacity over time, becoming limited-growth paraclones, a process called clonal conversion.
The molecular mechanisms driving clonal conversion remain largely unknown.

Purpose of the Study:

To investigate the molecular mechanisms underlying clonal conversion in cultured human epidermal keratinocytes.
To elucidate the role of actin organization and epidermal growth factor (EGF) signaling in stem cell fate.
To identify key molecular players, such as Rac1, involved in maintaining stem cell properties.

Main Methods:

Comparative analysis of actin filament organization in holoclones and paraclones.
Assessment of cellular responses to epidermal growth factor (EGF) in different cell states.
Pharmacological inhibition of key signaling pathways, including PI3K and Rac1, in holoclones.
Evaluation of cell proliferation and growth potential following molecular interventions.

Main Results:

Holoclones and paraclones exhibit distinct actin filament organization: radial in holoclones, circumferential in paraclones.
Actin organization dictates differential responses to EGF, promoting expansion in holoclones and reduction in paraclones.
Inhibition of PI3K or Rac1 in holoclones reorganizes actin filaments to resemble paraclones.
Sustained Rac1 inhibition in holoclones induces clonal conversion and diminishes growth potential.

Conclusions:

Actin filament organization is a key determinant of stem cell behavior and response to growth factors.
The Rac1 signaling pathway is critical for maintaining the proliferative capacity and stemness of keratinocyte holoclones.
Loss of stem cell function (clonal conversion) is linked to altered EGF-induced colony dynamics regulated by Rac1.