Published online 20 October 2005
Article |
Use of altered-specificity binding Oct-4 suggests an absence of pluripotent cell-specific cofactor usage
King's College London, Department of Haematological and Molecular Medicine, King's College School of Medicine, The Rayne Institute 123 Coldharbour Lane, London SE5 9NU, UK
*To whom correspondence should be addressed. Tel: +44 207 848 5813; Fax: +44 207 733 3877; Email: Alexander.e.smith{at}kcl.ac.uk
Received June 9, 2005. Revised September 29, 2005. Accepted September 29, 2005.
Oct-4 is a POU domain transcription factor that is critical for maintaining pluripotency and for stem cell renewal. Previous studies suggest that transcription regulation by Oct-4 at particular enhancers requires the input of a postulated E1A-like cofactor that is specific to pluripotent cells. However, such studies have been limited to the use of enhancer elements that bind other POU-protein family members in addition to Oct-4, thus preventing a clean assessment of any Oct-4:cofactor relationships. Other attempts to study Oct-4 functionality in a more stand-alone situation target Oct-4 transactivation domains to DNA using heterologous binding domains, a methodology which is known to generate artificial data. To circumvent these issues, an altered-specificity binding Oct-4 (Oct-4RR) and accompanying binding site, which binds Oct-4RR only, were generated. This strategy has previously been shown to maintain Oct-1:cofactor interactions that are highly binding-site and protein/binding conformation specific. This system therefore allows a stand-alone study of Oct-4 function in pluripotent versus differentiated cells, without interference from endogenous POU factors and with minimal deviation from bound wild-type protein characteristics. Subsequently, it was demonstrated that Oct-4RR and the highly transactive regions of its N-terminus determined here, and its C-terminus, have the same transactivation profile in pluripotent and differentiated cells, thus providing strong evidence against the existence of such a pluripotent cell-specific Oct-4 cofactor.