One of the four ingredients in the genetic recipe that scientists in Japan and the U.S. followed last year to persuade human skin cells to revert to an embryonic stem cell state, is dispensable in ES cells, thanks to the presence of a molecular alliance between a specific group of key proteins known as transcription factors, a research team led by the Genome Institute of Singapore (GIS) under the Agency for Science, Technology and Research (A*STAR) reports in the current issue of Nature Cell Biology.
The reprogramming factor - Klf4, one of the transcription factors that determine whether a cell's genes are active or silent - has at least two other sibling molecules that will substitute Klf4 to maintain a pluripotent embryonic stem (ES) cell state, the GIS-led team said.
Klf4 (also known as gut-enriched Krüppel-like factor or Gklf) belongs to the Krüppel-like factor (Klf) family of transcription factors that regulate numerous biological processes including proliferation, differentiation, development and apoptosis, or programmed cell death.
Since reprogramming mature cells to the ES state may provide a ready source of tissue for biomedical research and clinical treatment of diseases such as Parkinson's and diabetes, several laboratories, including GIS, are trying to better understand and finely tune the reprogramming process.
The team looks for clues for what these reprogramming ingredients are doing in ES cells.
"Klf4 has been a mysterious player among the four reprogramming factors. As taking out Klf4 in ES cells did not have any apparent effects, it is difficult to reconcile why such a potent reprogramming factor has no role in ES cell biology," said GIS scientist Ng Huck Hui, Ph.D., who headed the research team. Other members of the team include researchers from the National University of Singapore and University of Illinois at Urbana-Champaign.
The GIS research team found that when Klf4 was depleted, Klf2 and Klf5 took over Klf4's role. To understand the molecular basis of the Klf4 redundancy, the scientists studied the DNA binding and transcription activation properties of the three Klfs and found that the profiles of the three Klfs were strikingly similar.
"Most important, the data showed that the other Klfs were bound to the target sites when one of them was depleted." said Dr. Ng. "These Krüppel-like factors form a very powerful alliance that work together on regulating common targets. The impact of losing one of them is masked by the other two sibling molecules."
For example, Klfs were found to regulate the Nanog gene and other key genes that must be active for ES cells to be pluripotent, or capable of differentiating into virtually any type of cells. Nanog gene is one of the key pluripotency genes in ES cells.
"We suggest that Nanog and other genes are key effectors for the biological functions of the Klfs in ES cells," Dr. Ng said.