Year 1

Transcription factors are central for establishing the cell type-specific gene expression patterns and are often regulated by post-translational modifications (PTMs) that occur in response to developmental and environmental cues. We have found that the pluripotency transcription factor SOX2 is modified by the enzyme OGT, which is central in the glucose nutrient-sensing pathway, in embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) (mouse and human). Our preliminary data in the mouse system showed that mutation of the modified residue affects SOX2 function during reprogramming to pluripotency and during self-renewal of pluripotent cells. Our preliminary data also implicate this PTM in regulating human SOX2, as the equivalent residue is also modified in human pluripotent cells. We have begun experiments to gain a molecular understanding of the OGT-dependent modification, termed O-GlcNAcylation, of SOX2 in reprogramming to pluripotency in human cells. Our aims are 1) to examine whether mutation of the modified SOX2 residue enhances human reprogramming, 2) to examine whether increasing OGT amounts or activity enhance human reprogramming (since OGT is expressed at much lower levels in somatic cells than pluripotent cells), and 3) to determine the molecular consequences of expressing the mutant form of SOX2 during reprogramming and in pluripotent cells (in this third aim we use mouse as a more genetically tractable model system to first investigate molecular mechanism and then examine the mechanisms implicated in the human system). Our results to date provide a molecular basis for the increased reprogramming efficiency observed with mutant SOX2: we find that SOX2 that cannot be modified causes increased expression of epigenetic modifiers that are necessary for successful reprogramming.