Restriction of Cellular Plasticity of Differentiated Cells Mediated by Chromatin Modifiers, Transcription Factors and Protein Kinases

Ectopic expression of master regulatory transcription factors can reprogram the identity of specific cell types. The effectiveness of such induced cellular reprogramming is generally greatly reduced if the cellular substrates are fully differentiated cells. For example, in the nematode C. elegans, the ectopic expression of a neuronal identity-inducing transcription factor, , can effectively induce target genes in immature cells but not in fully mature non-neuronal cells. To understand the molecular basis of this progressive restriction of cellular plasticity, we screened for C. elegans mutants in which ectopically expressed is able to induce neuronal effector genes in epidermal cells. We identified a ubiquitin hydrolase, , that restricts cellular plasticity with a notable cellular specificity. Even though we find to be very broadly expressed in all tissue types, null mutants specifically make epidermal cells susceptible to -mediated activation of neuronal target genes. We screened for additional genes that allow epidermal cells to be at least partially reprogrammed by ectopic expression and identified many additional proteins that restrict cellular plasticity of epidermal cells, including a chromatin-related factor (H3K79 methyltransferase, ), a transcription factor (nuclear hormone receptor ), two MAPK-type protein kinases ( and ), a nuclear localized O-GlcNAc transferase () and a member of large family of nuclear proteins related to the Rb-associated chromatin factor. These findings provide novel insights into the control of cellular plasticity.