The pluripotency rheostat Nanog functions as a dimer

Area of Science:

• Stem cell biology
• Molecular biology
• Protein biochemistry

Background:

• Nanog is a key transcription factor maintaining embryonic stem (ES) cell pluripotency and self-renewal.
• The precise molecular mechanisms underlying Nanog's function in ES cell self-renewal remain largely unelucidated.
• Understanding Nanog's biochemical interactions is critical for controlling stem cell fate.

Purpose of the Study:

• To investigate the biochemical basis of Nanog's function in conferring cytokine-independent self-renewal to ES cells.
• To identify the specific domain and mechanism responsible for Nanog self-association.
• To determine the functional significance of Nanog dimerization in ES cell self-renewal.

Main Methods:

• Co-immunoprecipitation assays using epitope-tagged Nanog variants.
• In vitro protein binding experiments.
• Analytical ultracentrifugation to assess protein in solution.
• Embryonic stem cell colony-forming assays.

Main Results:

• Nanog self-associates through a functionally critical domain characterized by a tryptophan-repeat region.
• In vitro experiments confirmed direct participation of this region in Nanog self-association.
• Analytical ultracentrifugation revealed Nanog exists in equilibrium between monomeric and dimeric forms (Kd = 3 μM).
• Deletion of the tryptophan-repeat region abolished Nanog's ability to promote leukemia inhibitory factor (LIF)-independent self-renewal in ES cells.

Conclusions:

• Nanog dimerization is a critical mechanism for its role in maintaining ES cell self-renewal.
• The identified tryptophan-repeat domain is essential for Nanog self-association and function.
• These findings provide biochemical insight into how Nanog regulates stem cell pluripotency.