A gene whose altered expression has previously associated with human leukaemias and Ewing’s sarcoma?a type of malignant bone tumour found in young adults?is required for the proper functioning of blood stem cells. In a study published online this week in Nature Immunology, scientists report that the gene, known as Erg, maintains normal numbers of blood stem cells that generate a constant supply of short-lived mature cells in the blood.

Using a genetic screen in mice, Benjamin Kile and co-workers uncovered a mutation in the Erg gene that affects stem cell populations. By evaluating the capacity of different populations of primitive blood cells to form mature blood cells, they determined that production and/or survival of blood stem cells is reduced in mice with the Erg mutation. Thus some mutations in Erg lead to reduced numbers of blood stem cells while others are associated with human leukaemias.

This finding uncovers a key function of Erg independent of its effects on human cancers and demonstrates the importance of using mouse models and genetic screens to identify the influence of specific genes involved in human cancers and other human diseases.