Cell memory and cancer - the story of the trithorax and Polycomb group genes

Most of the cells in an adult organism possess the same DNA content and the same complement of genes, yet we can recognise many different cell types i n the adult. Development is the process by which the cells of the embryo pr ogressively acquire their adult fate and position. The genetic network whic h controls these processes is beginning to be unravelled at an increasing p ace, yet one key area is still somewhat neglected - namely, developmental c ell memory, the process by which cells record their ontogeny. A significant component of the phenotype of cancer cells may be explained by deregulatio n of genes whose normal role is to control the division, differentiation an d migration of embryonic cells during development. It should therefore not be surprising that genes implicated in cell memory processes during develop ment are also implicated in disease. In this review we outline what is know n about the Polycomb and trithorax group of proteins as candidate genes for the memory process, both in terms of basic functions and the roles of abno rmalities in these genes resulting in cancer.