During organ development, a delicate balance between proliferation and terminal differentiation of progenitor cells ensures that the final organ has the correct size and structure. On , Okubo and co-workers report that Nmyc is required to maintain this balance in developing mouse lungs. They show that Nmyc expression in mouse embryonic lung is restricted to a distal population of undifferentiated epithelial cells, many of which are in the S phase of the cell cycle. Overexpression of Nmyc in the epithelium of the developing lung increases the domain of S phase cells and inhibits differentiation; deletion of one or two copies of Nmyc produces the opposite outcomes. Thus,the researchers suggest, Nmyc's role in lung development is to maintain a distal population of undifferentiated, proliferating progenitor cells, a discovery that may help us to understand disorders such as lung cancer.
