Self-Organization of Whole Gene Expression through Coordinated Chromatin Structural Transition

The human DNA molecule is a 2 meters long polymer collapsed into the micrometer space of the cell nucleus. This simple consideration rules out any ‘Maxwell demon’- like explanation of regulation in which a single regulatory molecule (e.g., a transcription factor) finds autonomously its way to the particular target gene whose expression must be repressed or enhanced. A gene-by-gene regulation is still more contrasting with physical reality when in presence of cell state transitions involving the contemporary expression change of thousands of genes. This state of affair asks for a statistical mechanics inspired approach where specificity arises from a selective unfolding of chromatin driving the rewiring of gene expression pattern. The arising of ‘expression waves’ marking state transitions related to chromatin structural reorganization through self-organized critical control (SOC) of whole genome expression will be described in the present paper. We adopt as model system the gene expression time course of a cancer cell (MCF-7) population exposed to an efficient (HRG) stimulus causing a state transition in comparison to an ineffective (EGF) stimulus. The obtained results will be put into the perspective of biological adaptive systems living on the ‘edge of chaos’.