Multicellular organisms are made up of diverse populations of many different types of cells, each of which contains an identical set of genetic information coded in its DNA. Cell differentiation and the process of development itself depend on the ability of individual cells to maintain the expression of different genes. In recent years, we have begun to understand that the maintenance of specific patterns of gene expression does not rely on direct modifications to the DNA sequence encoding the organism's genome, but rather takes place in a heritable, “epigenetic” manner. Our laboratory investigates how modifications to the structure and configuration of chromatin (complexes of nuclear DNA and proteins that provide the structural basis of chromosomes) contribute to epigenetic gene regulation and and how such modifications are transmitted over generations of cellular division by studying events at the molecular scale in the model organism, fission yeast (Schizosaccharomyces pombe), in cultured mammalian cells, and in ciliate Tetrahymena.