Transcription factors decide stem cell identity
29 Jan 2016 NUS scientists investigated how different transcription factors (TFs) interact in embryonic and neuronal stem cells (ESC and NSC).
Transcription factors are proteins that bind DNA and control the rate of gene transcription, thus influencing cell functions. In 2006, it was discovered that the expression of only four TFs (Sox2, c-Myc, Klf4, and Oct4) can reprogramme fibroblast cells to pluripotency. NSCs express the first three of these factors but instead of Oct4 they express Oct6. The expression of Oct4 alone in NSCs can convert the cells to pluripotency. This raises the question of how the expression of Oct4 alone converts NSCs to pluripotency and the differences between Oct4 and Oct6.
A team lead by Prof Thorsten WOHLAND from the Department of Chemistry and the Department of Biological Sciences in NUS, Prof Paul ROBSON from the Genome Institute of Singapore (GIS) under A*STAR and Ian CHAMBERS from the University of Edinburgh investigated the interaction of Sox2, Oct4 and Oct 6 during DNA binding. They used a newly developed fluorescence protein-based electromobility shift assay (FP-EMSA) in conjunction with fluorescence correlation spectroscopy (FCS), and ChipSeq data to show the following: a) Oct4 binds equally to Sox/Oct and MORE. DNA motifs, while Oct6 binds preferentially to MORE; b)The presence of Sox2 enhances Oct4 binding to the Sox/Oct motif but has little influence on Oct6, and c) MORE is the most enriched motif for Oct6 in NSCs while Sox/Oct is the most enriched motif for Sox2 and Oct4 in ESCs. Together, these discoveries offer a mechanism for the creation of induced pluripotent stem cells from NSCs (see Figure). In the future, a similar approach could be used to test synergistic interaction of other transcription factors to elucidate the molecular mechanisms behind cell fate decisions.
The figure shows Sox2 and POU-TF subclasses have distinct interactions and distinguish pluripotent ESCs from multipotent NSCs. The different combinations of TFs and DNA binding motifs in ESCs and NSCs provide a mechanism on how Oct4 alone can convert NSCs to pluripotency [Image credit: Thorsten Wohland].
Mistri TK, AG Devasia, LT Chu, WP Ng, F Halbritter, D Colby, B Martynoga, SR Tomlinson, I Chambers, P Robson, T Wohland. “Selective influence of Sox2 on POU transcription factor binding in embryonic and neural stem cells.” EMBO Rep. 16 (2015) 1177.