During development, cell division and cell specification must be coordinated to ensure that the tissues and organs of the adult organism are the correct size and contain the right proportions of various cell types. Here (p. ), Adrienne Roeder and colleagues investigate how developmental regulators interact with the cell cycle in Arabidopsis sepals to create a characteristic pattern of outer epidermal cells in which elongated giant cells, which are produced by endoreduplication (DNA replication without cell division), are interspersed between small cells, which divide mitotically. They show that distinct enhancers are expressed in giant cells and small cells, which suggests that these cells have different identities as well as different sizes and ploidies. Several members of the epidermal specification pathway control the identity of giant cells, they report, which is established upstream of cell-cycle regulation. By contrast, endoreduplication represses small cell identity. Thus, suggest the researchers, cell type affects cell-cycle regulation but, in addition, cell-cycle regulation can control cell identity.
