elf-renewal of embryonic stem (ES) cells depends on the activity of a network of transcription factors at the centre of which lies the triumvirate of Nanog, Oct4 and Sox2 that bind together to a multitude of target genes to either activate or repress their expression. Nanog was initially isolated by the host laboratory on the basis that elevating its expression increased ES cell self-renewal efficiency. Surprisingly however, the host laboratory further demonstrated that ES cells continue to self-renew in the absence of Nanog, albeit with dramatically reduced efficiency. Moreover, Nanog is not expressed uniformly within the Oct4/Sox2-expressing undifferentiated population.
Instead, ES cells fluctuate between a state in which Nanog protein levels are low or absent, associated with a poor self-renewal efficiency, and a state in which Nanog levels are high, associated with a high self-renewal efficiency. In order to shed light upon the means by which these fluctuations direct altered cellular functions, we propose a project with the specific aims of (i) determining the gene expression profile in ES cells expressing distinct forms of Nanog, (ii) analysing the co-dependency of chromatin binding by Nanog, Oct4 and Sox2 at relevant target genes, and (iii) test the functional importance of the most relevant Nanog responsiveness genes.