The cerebrospinal fluid (CSF) that bathes the brain and spinal cord seems to be more than just a cushion against shock. Key molecules in the CSF signal neural stem cells to proliferate, and may be involved in a type of brain cancer.

Christopher Walsh at the Children's Hospital Boston in Massachusetts and his colleagues found that membrane proteins on the surface of neural stem cells facing the CSF bind to proteins, including insulin-like growth factor 2 (Igf2), in the fluid. Blocking this binding in mice resulted in animals with small brains.

Patients with a type of brain tumour were found to have higher than normal levels of Igf2 in their CSF.

Neuron 69, 893–905 (2011)