While all cells in the human body contain the same DNA (genetic instructions), each cell expresses only the genes needed to become the cell type it is (i.e. neuron, lymphocyte, cardiomyocytes). Each cell’s fate is largely determined by chemical modifications to the histone proteins around the DNA, which control gene expression. Considering that these cells lose half of their modifications when replicating in cell division, a new MIT study suggests that these cells maintain their memory of what cell type they’re supposed to be through the 3D folding pattern of its genome determining which portions will be marked by chemical modifications. Essentially, the way that these chromosomes were folded are like a blueprint to determine where the remaining marks should go. Thus, by juggling between 3D folding and the marks, the epigenetic memory can be preserved over hundreds of divisions.
In general, this proposed model provides valuable insight into how epigenetic markings play a role in establishing cell identity and maintaining this memory after cell division. Through this model, biologists may be able to better understand how this epigenetic memory of cell identity is lost as cells begin to age and potentially better understand the epigenetic mechanisms underlying our genome.